Theories, Hypotheses, and Laws | Process of Science

<!DOCTYPE html> <html lang="en" dir="ltr"> <head>  <meta http-equiv="X-UA-Compatible" content="ie=edge"> <meta charset="utf-8"> <base href="https://www.visionlearning.com"> <title>Theories, Hypotheses, and Laws | Process of Science | Visionlearning</title> <link rel="canonical" href="https://www.visionlearning.com/en/library/process-of-science/49/theories-hypotheses-and-laws/177"> <meta name="description" content="Learn how scientific theories are built and revised. Uses the theory of evolution through natural selection to show the process of testing, expanding, and refining ideas."> <meta name="keywords" content="What is a hypothesis, Scientific theory vs law, Define scientific theory and law, Example of scientific theory, What is the scientific method"> <meta name="viewport" content="width=device-width, initial-scale=1.0, shrink-to-fit=no"> <meta name="msvalidate.01" content="D8E20F39AD48052260032E56DE409970"> <script type="application/ld+json"> { "@context": "http://schema.org/", "@type": "Article", "mainEntityOfPage": { "@type": "WebPage", "@id": "https://visionlearning.com/en/library/process-of-science/49/theories-hypotheses-and-laws/177" }, "name": "Theories, Hypotheses, and Laws", "headline": "Theories, Hypotheses, and Laws: Definitions, examples, and their roles in science", "author": [ { "@type": "Person", "name": "Anthony Carpi, Ph.D." } , { "@type": "Person", "name": "Anne E. Egger, Ph.D." }], "datePublished": "2009-12-19 06:09:53", "dateModified": "2017-02-12T08:30:00+05:00", "image": { "@type": "ImageObject", "url": "/img/library/moduleImages/featured_image_177-23061210061323.jpeg", "width": 696, "height": 464 }, "publisher": { "@type": "Organization", "name": "Visionlearning, Inc.", "logo": { "@type": "ImageObject", "url": "http://visionlearning.com/images/logo.png", "width": 278, "height": 60 } }, "description": "Theories are not based on one scientist's work but on an accumulation of evidence and ideas from many scientists over time. This module discusses how scientific theories are built and revised. It uses the development of the theory of evolution through natural selection to illustrate how theories are built through a process of testing, expanding, and refining.", "keywords": "What is a hypothesis, Scientific theory vs law, Define scientific theory and law, Example of scientific theory, What is the scientific method", "inLanguage": { "@type": "Language", "name": "English", "alternateName": "en" }, "copyrightHolder": { "@type": "Organization", "name": "Visionlearning, Inc." }, "copyrightYear": "2009"} </script> <meta property="og:url" content="https://visionlearning.com/en/library/process-of-science/49/theories-hypotheses-and-laws/177"> <meta property="og:title" content="Theories, Hypotheses, and Laws | Process of Science | Visionlearning" /> <meta property="og:type" content="website"> <meta property="og:site_name" content="Visionlearning"> <meta property="og:description" content="Learn how scientific theories are built and revised. 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aria-controls="acc-panel-hazards" aria-expanded="false"> <span class="accordion__button__label"> Hazards </span> </button> <div class="accordion__panel" id="acc-panel-hazards" data-accordion="panel" aria-labelledby="acc-button-hazards" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/earth-science/6/natural-hazards-and-risk/288">Natural Hazards and Risk</a></li> </ul> </div> <button class="accordion__button" id="acc-button-earth-history" data-accordion="button" aria-controls="acc-panel-earth-history" aria-expanded="false"> <span class="accordion__button__label"> Earth History </span> </button> <div class="accordion__panel" id="acc-panel-earth-history" data-accordion="panel" aria-labelledby="acc-button-earth-history" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/earth-science/6/extinction/295">Extinction</a></li> <li><a href="/en/library/earth-science/6/mass-extinctions/294">Mass Extinctions</a></li> </ul> </div> </div> </div> <button 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<li><a href="/en/library/environmental-science/61/ecosystem-services/279">Ecosystem Services</a></li> <li><a href="/en/library/environmental-science/61/population-biology/287">Population Biology</a></li> </ul> </div> <button class="accordion__button" id="acc-button-earth-cycles" data-accordion="button" aria-controls="acc-panel-earth-cycles" aria-expanded="false"> <span class="accordion__button__label"> Earth Cycles </span> </button> <div class="accordion__panel" id="acc-panel-earth-cycles" data-accordion="panel" aria-labelledby="acc-button-earth-cycles" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/environmental-science/61/the-nitrogen-cycle/98">The Nitrogen Cycle</a></li> <li><a href="/en/library/environmental-science/61/the-carbon-cycle/95">The Carbon Cycle</a></li> <li><a href="/en/library/environmental-science/61/the-phosphorus-cycle/197">The Phosphorus Cycle</a></li> </ul> </div> <button class="accordion__button" id="acc-button-scientific-research" data-accordion="button" aria-controls="acc-panel-scientific-research" aria-expanded="false"> <span class="accordion__button__label"> Scientific Research </span> </button> <div class="accordion__panel" id="acc-panel-scientific-research" data-accordion="panel" aria-labelledby="acc-button-scientific-research" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/environmental-science/61/collaborative-research-in-the-arctic-towards-understanding-climate-change/183">Collaborative Research in the Arctic Towards Understanding Climate Change</a></li> <li><a href="/en/library/environmental-science/61/atmospheric-chemistry-research-that-changed-global-policy/211">Atmospheric Chemistry Research that Changed Global Policy</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-general-science" data-accordion="button" aria-controls="acc-panel-general-science" aria-expanded="false"> <span class="accordion__button__label"> General Science </span> </button> <div class="accordion__panel" id="acc-panel-general-science" data-accordion="panel" aria-labelledby="acc-button-general-science" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-methods" data-accordion="button" aria-controls="acc-panel-methods" aria-expanded="false"> <span class="accordion__button__label"> Methods </span> </button> <div class="accordion__panel" id="acc-panel-methods" data-accordion="panel" aria-labelledby="acc-button-methods" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/general-science/3/the-scientific-method/45">The Scientific Method</a></li> </ul> </div> <button class="accordion__button" id="acc-button-measurement" data-accordion="button" aria-controls="acc-panel-measurement" aria-expanded="false"> <span class="accordion__button__label"> Measurement </span> </button> <div class="accordion__panel" id="acc-panel-measurement" data-accordion="panel" aria-labelledby="acc-button-measurement" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/general-science/3/the-metric-system/47">The Metric System</a></li> </ul> </div> <button class="accordion__button" id="acc-button-physical-properties" data-accordion="button" aria-controls="acc-panel-physical-properties" aria-expanded="false"> <span class="accordion__button__label"> Physical Properties </span> </button> <div class="accordion__panel" id="acc-panel-physical-properties" data-accordion="panel" aria-labelledby="acc-button-physical-properties" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/general-science/3/temperature/48">Temperature</a></li> <li><a href="/en/library/general-science/3/density-and-buoyancy/37">Density and Buoyancy</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-math-in-science" data-accordion="button" aria-controls="acc-panel-math-in-science" aria-expanded="false"> <span class="accordion__button__label"> Math in Science </span> </button> <div class="accordion__panel" id="acc-panel-math-in-science" data-accordion="panel" aria-labelledby="acc-button-math-in-science" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-equations" data-accordion="button" aria-controls="acc-panel-equations" aria-expanded="false"> <span class="accordion__button__label"> Equations </span> </button> <div class="accordion__panel" id="acc-panel-equations" data-accordion="panel" aria-labelledby="acc-button-equations" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/math-in-science/62/unit-conversion/144">Unit Conversion</a></li> <li><a href="/en/library/math-in-science/62/linear-equations/194">Linear Equations</a></li> <li><a href="/en/library/math-in-science/62/exponential-equations-i/206">Exponential Equations I</a></li> <li><a href="/en/library/math-in-science/62/exponential-equations-ii/210">Exponential Equations II</a></li> <li><a href="/en/library/math-in-science/62/scientific-notation/250">Scientific Notation</a></li> <li><a href="/en/library/math-in-science/62/measurement/257">Measurement</a></li> </ul> </div> <button class="accordion__button" id="acc-button-statistics" data-accordion="button" aria-controls="acc-panel-statistics" aria-expanded="false"> <span class="accordion__button__label"> Statistics </span> </button> <div class="accordion__panel" id="acc-panel-statistics" data-accordion="panel" aria-labelledby="acc-button-statistics" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/math-in-science/62/introduction-to-descriptive-statistics/218">Introduction to Descriptive Statistics</a></li> <li><a href="/en/library/math-in-science/62/introduction-to-inferential-statistics/224">Introduction to Inferential Statistics</a></li> <li><a href="/en/library/math-in-science/62/statistical-techniques/239">Statistical Techniques</a></li> </ul> </div> <button class="accordion__button" id="acc-button-trigonometric-functions" data-accordion="button" aria-controls="acc-panel-trigonometric-functions" aria-expanded="false"> <span class="accordion__button__label"> Trigonometric Functions </span> </button> <div class="accordion__panel" id="acc-panel-trigonometric-functions" data-accordion="panel" aria-labelledby="acc-button-trigonometric-functions" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/math-in-science/62/wave-mathematics/131">Wave Mathematics</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-physics" data-accordion="button" aria-controls="acc-panel-physics" aria-expanded="false"> <span class="accordion__button__label"> Physics </span> </button> <div class="accordion__panel" id="acc-panel-physics" data-accordion="panel" aria-labelledby="acc-button-physics" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-light-and-optics" data-accordion="button" aria-controls="acc-panel-light-and-optics" aria-expanded="false"> <span class="accordion__button__label"> Light and Optics </span> </button> <div class="accordion__panel" id="acc-panel-light-and-optics" data-accordion="panel" aria-labelledby="acc-button-light-and-optics" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/physics/24/the-nature-of-light/132">The Nature of Light</a></li> <li><a href="/en/library/physics/24/electromagnetism-and-light/138">Electromagnetism and Light</a></li> </ul> </div> <button class="accordion__button" id="acc-button-mechanics" data-accordion="button" aria-controls="acc-panel-mechanics" aria-expanded="false"> <span class="accordion__button__label"> Mechanics </span> </button> <div class="accordion__panel" id="acc-panel-mechanics" data-accordion="panel" aria-labelledby="acc-button-mechanics" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/physics/24/defining-energy/199">Defining Energy</a></li> <li><a href="/en/library/physics/24/waves-and-wave-motion/102">Waves and Wave Motion</a></li> <li><a href="/en/library/physics/24/gravity/118">Gravity</a></li> <li><a href="/en/library/physics/24/thermodynamics-i/200">Thermodynamics I</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-process-of-science" data-accordion="button" aria-controls="acc-panel-process-of-science" aria-expanded="false"> <span class="accordion__button__label"> Process of Science </span> </button> <div class="accordion__panel" id="acc-panel-process-of-science" data-accordion="panel" aria-labelledby="acc-button-process-of-science" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-introduction" data-accordion="button" aria-controls="acc-panel-introduction" aria-expanded="false"> <span class="accordion__button__label"> Introduction </span> </button> <div class="accordion__panel" id="acc-panel-introduction" data-accordion="panel" aria-labelledby="acc-button-introduction" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/the-process-of-science/176">The Process of Science</a></li> </ul> </div> <button class="accordion__button" id="acc-button-the-culture-of-science" data-accordion="button" aria-controls="acc-panel-the-culture-of-science" aria-expanded="false"> <span class="accordion__button__label"> The Culture of Science </span> </button> <div class="accordion__panel" id="acc-panel-the-culture-of-science" data-accordion="panel" aria-labelledby="acc-button-the-culture-of-science" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/the-nature-of-scientific-knowledge/185">The Nature of Scientific Knowledge</a></li> <li><a href="/en/library/process-of-science/49/scientists-and-the-scientific-community/172">Scientists and the Scientific Community</a></li> <li><a href="/en/library/process-of-science/49/scientific-ethics/161">Scientific Ethics</a></li> <li><a href="/en/library/process-of-science/49/scientific-institutions-and-societies/162">Scientific Institutions and Societies</a></li> </ul> </div> <button class="accordion__button" id="acc-button-ideas-in-science" data-accordion="button" aria-controls="acc-panel-ideas-in-science" aria-expanded="false"> <span class="accordion__button__label"> Ideas in Science </span> </button> <div class="accordion__panel" id="acc-panel-ideas-in-science" data-accordion="panel" aria-labelledby="acc-button-ideas-in-science" role="region"> <ul class="nav text-color-link"> <li class="current">Theories, Hypotheses, and Laws</li> <li><a href="/en/library/process-of-science/49/scientific-controversy/181">Scientific Controversy</a></li> <li><a href="/en/library/process-of-science/49/creativity-in-science/182">Creativity in Science</a></li> </ul> </div> <button class="accordion__button" id="acc-button-research-methods" data-accordion="button" aria-controls="acc-panel-research-methods" aria-expanded="false"> <span class="accordion__button__label"> Research Methods </span> </button> <div class="accordion__panel" id="acc-panel-research-methods" data-accordion="panel" aria-labelledby="acc-button-research-methods" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/the-practice-of-science/148">The Practice of Science</a></li> <li><a href="/en/library/process-of-science/49/experimentation-in-scientific-research/150">Experimentation in Scientific Research</a></li> <li><a href="/en/library/process-of-science/49/description-in-scientific-research/151">Description in Scientific Research</a></li> <li><a href="/en/library/process-of-science/49/comparison-in-scientific-research/152">Comparison in Scientific Research</a></li> <li><a href="/en/library/process-of-science/49/modeling-in-scientific-research/153">Modeling in Scientific Research</a></li> </ul> </div> <button class="accordion__button" id="acc-button-data" data-accordion="button" aria-controls="acc-panel-data" aria-expanded="false"> <span class="accordion__button__label"> Data </span> </button> <div class="accordion__panel" id="acc-panel-data" data-accordion="panel" aria-labelledby="acc-button-data" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/data-analysis-and-interpretation/154">Data Analysis and Interpretation</a></li> <li><a href="/en/library/process-of-science/49/uncertainty-error-and-confidence/157">Uncertainty, Error, and Confidence</a></li> <li><a href="/en/library/process-of-science/49/statistics-in-science/155">Statistics in Science</a></li> <li><a href="/en/library/process-of-science/49/using-graphs-and-visual-data-in-science/156">Using Graphs and Visual Data in Science</a></li> </ul> </div> <button class="accordion__button" id="acc-button-scientific-communication" data-accordion="button" aria-controls="acc-panel-scientific-communication" aria-expanded="false"> <span class="accordion__button__label"> Scientific Communication </span> </button> <div class="accordion__panel" id="acc-panel-scientific-communication" data-accordion="panel" aria-labelledby="acc-button-scientific-communication" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/understanding-scientific-journals-and-articles/158">Understanding Scientific Journals and Articles</a></li> <li><a href="/en/library/process-of-science/49/utilizing-the-scientific-literature/173">Utilizing the Scientific Literature</a></li> <li><a href="/en/library/process-of-science/49/peer-review-in-scientific-publishing/159">Peer Review in Scientific Publishing</a></li> <li><a href="/en/library/process-of-science/49/the-how-and-why-of-scientific-meetings/186">The How and Why of Scientific Meetings</a></li> </ul> </div> </div> </div> <button class="accordion__button" id="acc-button-scientists-and-research" data-accordion="button" aria-controls="acc-panel-scientists-and-research" aria-expanded="false"> <span class="accordion__button__label"> Scientists and Research </span> </button> <div class="accordion__panel" id="acc-panel-scientists-and-research" data-accordion="panel" aria-labelledby="acc-button-scientists-and-research" role="region"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-button-scientific-research" data-accordion="button" aria-controls="acc-panel-scientific-research" aria-expanded="false"> <span class="accordion__button__label"> Scientific Research </span> </button> <div class="accordion__panel" id="acc-panel-scientific-research" data-accordion="panel" aria-labelledby="acc-button-scientific-research" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/scientists-and-research/58/collaborative-research-in-the-arctic-towards-understanding-climate-change/183">Collaborative Research in the Arctic Towards Understanding Climate Change</a></li> <li><a href="/en/library/scientists-and-research/58/from-stable-chromosomes-to-jumping-genes/184">From Stable Chromosomes to Jumping Genes</a></li> <li><a href="/en/library/scientists-and-research/58/an-elegant-experiment-to-test-the-process-of-dna-replication/187">An Elegant Experiment to Test the Process of DNA Replication</a></li> <li><a href="/en/library/scientists-and-research/58/the-founding-of-neuroscience/233">The Founding of Neuroscience</a></li> <li><a href="/en/library/scientists-and-research/58/tracking-endangered-jaguars-across-the-border/189">Tracking Endangered Jaguars across the Border</a></li> <li><a href="/en/library/scientists-and-research/58/atmospheric-chemistry-research-that-changed-global-policy/211">Atmospheric Chemistry Research that Changed Global Policy</a></li> <li><a href="/en/library/scientists-and-research/58/revolutionizing-medicine-with-monoclonal-antibodies/220">Revolutionizing Medicine with Monoclonal Antibodies</a></li> <li><a href="/en/library/scientists-and-research/58/uncovering-the-mysteries-of-chronic-mountain-sickness/238">Uncovering the Mysteries of Chronic Mountain Sickness</a></li> </ul> </div> <button class="accordion__button" id="acc-button-profiles-in-science" data-accordion="button" aria-controls="acc-panel-profiles-in-science" aria-expanded="false"> <span class="accordion__button__label"> Profiles in Science </span> </button> <div class="accordion__panel" id="acc-panel-profiles-in-science" data-accordion="panel" aria-labelledby="acc-button-profiles-in-science" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/scientists-and-research/58/luis-e.-miramontes/232">Luis E. Miramontes</a></li> <li><a href="/en/library/scientists-and-research/58/bernardo-houssay/237">Bernardo Houssay</a></li> <li><a href="/en/library/scientists-and-research/58/craig-lee/256">Craig Lee</a></li> <li><a href="/en/library/scientists-and-research/58/david-ho/241">David Ho</a></li> <li><a href="/en/library/scientists-and-research/58/louis-tompkins-wright/244">Louis Tompkins Wright</a></li> <li><a href="/en/library/scientists-and-research/58/carlos-j.-finlay/217">Carlos J. Finlay</a></li> <li><a href="/en/library/scientists-and-research/58/cecilia-payne/290">Cecilia Payne</a></li> <li><a href="/en/library/scientists-and-research/58/jazmin-scarlett/291">Jazmin Scarlett</a></li> <li><a href="/en/library/scientists-and-research/58/ramari-stewart/292">Ramari Stewart</a></li> <li><a href="/en/library/scientists-and-research/58/johnson-cerda/300">Johnson Cerda</a></li> <li><a href="/en/library/scientists-and-research/58/ellen-ochoa/201">Ellen Ochoa</a></li> <li><a href="/en/library/scientists-and-research/58/ruth-benerito/205">Ruth Benerito</a></li> <li><a href="/en/library/scientists-and-research/58/franklin-chang-díaz/219">Franklin Chang Díaz</a></li> <li><a href="/en/library/scientists-and-research/58/percy-lavon-julian/221">Percy Lavon Julian</a></li> <li><a href="/en/library/scientists-and-research/58/luis-walter-alvarez/229">Luis Walter Alvarez</a></li> <li><a href="/en/library/scientists-and-research/58/france-anne-dominic-córdova/230">France Anne-Dominic Córdova</a></li> </ul> </div> </div> </div> </div> </div> </li> <li>  <button class="button" data-toggle="dropdown">Process of Science </button> <div class="nav__dropdown box-shadow-1 padding-1"> <div class="accordion accordion--secondary font-size-sm"> <div class="accordion accordion--secondary"> <button class="accordion__button" id="acc-sub-button-introduction" data-accordion="button" aria-controls="acc-sub-panel-introduction" aria-expanded="false"> <span class="accordion__button__label"> Introduction </span> </button> <div class="accordion__panel" id="acc-sub-panel-introduction" data-accordion="panel" aria-labelledby="acc-sub-button-introduction" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/the-process-of-science/176">The Process of Science</a></li> </ul> </div> <button class="accordion__button" id="acc-sub-button-the-culture-of-science" data-accordion="button" aria-controls="acc-sub-panel-the-culture-of-science" aria-expanded="false"> <span class="accordion__button__label"> The Culture of Science </span> </button> <div class="accordion__panel" id="acc-sub-panel-the-culture-of-science" data-accordion="panel" aria-labelledby="acc-sub-button-the-culture-of-science" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/the-nature-of-scientific-knowledge/185">The Nature of Scientific Knowledge</a></li> <li><a href="/en/library/process-of-science/49/scientists-and-the-scientific-community/172">Scientists and the Scientific Community</a></li> <li><a href="/en/library/process-of-science/49/scientific-ethics/161">Scientific Ethics</a></li> <li><a href="/en/library/process-of-science/49/scientific-institutions-and-societies/162">Scientific Institutions and Societies</a></li> </ul> </div> <button class="accordion__button" id="acc-sub-button-ideas-in-science" data-accordion="button" aria-controls="acc-sub-panel-ideas-in-science" aria-expanded="false"> <span class="accordion__button__label"> Ideas in Science </span> </button> <div class="accordion__panel" id="acc-sub-panel-ideas-in-science" data-accordion="panel" aria-labelledby="acc-sub-button-ideas-in-science" role="region"> <ul class="nav text-color-link"> <li class="current">Theories, Hypotheses, and Laws</li> <li><a href="/en/library/process-of-science/49/scientific-controversy/181">Scientific Controversy</a></li> <li><a href="/en/library/process-of-science/49/creativity-in-science/182">Creativity in Science</a></li> </ul> </div> <button class="accordion__button" id="acc-sub-button-research-methods" data-accordion="button" aria-controls="acc-sub-panel-research-methods" aria-expanded="false"> <span class="accordion__button__label"> Research Methods </span> </button> <div class="accordion__panel" id="acc-sub-panel-research-methods" data-accordion="panel" aria-labelledby="acc-sub-button-research-methods" role="region"> <ul class="nav text-color-link"> <li><a href="/en/library/process-of-science/49/the-practice-of-science/148">The Practice of Science</a></li> <li><a href="/en/library/process-of-science/49/experimentation-in-scientific-research/150">Experimentation in Scientific Research</a></li> <li><a href="/en/library/process-of-science/49/description-in-scientific-research/151">Description in Scientific Research</a></li> <li><a href="/en/library/process-of-science/49/comparison-in-scientific-research/152">Comparison in Scientific Research</a></li> <li><a href="/en/library/process-of-science/49/modeling-in-scientific-research/153">Modeling in Scientific Research</a></li> </ul> </div> <button class="accordion__button" id="acc-sub-button-data" data-accordion="button" aria-controls="acc-sub-panel-data" aria-expanded="false"> <span class="accordion__button__label"> Data </span> </button> <div class="accordion__panel" id="acc-sub-panel-data" data-accordion="panel" aria-labelledby="acc-sub-button-data" role="region"> <ul class="nav 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<li><a href="/en/library/process-of-science/49/understanding-scientific-journals-and-articles/158">Understanding Scientific Journals and Articles</a></li> <li><a href="/en/library/process-of-science/49/utilizing-the-scientific-literature/173">Utilizing the Scientific Literature</a></li> <li><a href="/en/library/process-of-science/49/peer-review-in-scientific-publishing/159">Peer Review in Scientific Publishing</a></li> <li><a href="/en/library/process-of-science/49/the-how-and-why-of-scientific-meetings/186">The How and Why of Scientific Meetings</a></li> </ul> </div> </div> </div> </div> </li> </ul> </nav>  <div id="theTop"></div> <main id="skip-header-content"> <div class="margin-bottom-5"> <article class="container wide module"> <header class="grid grid--sidebar-right module__header"> <div class="module__header__title"> <span class="subcategory"> <strong><em>Ideas in Science</em></strong> </span> <h1>Theories, Hypotheses, and Laws: <sub><em>Definitions, examples, and their roles in science</em></sub></h1> <p class="byline">by Anthony Carpi, Ph.D., Anne E. Egger, Ph.D.</p> <nav class="module__header__tabs"> <ul class="tabs-nav tabs-nav--horizontal library"> <li> <a href="/en/library/process-of-science/49/theories-hypotheses-and-laws/177/reading" aria-current="page" >Reading</a> </li> <li> <a href="/en/library/process-of-science/49/theories-hypotheses-and-laws/177/quiz">Quiz</a> </li> <li> <a href="/en/library/process-of-science/49/theories-hypotheses-and-laws/177/resources">Teach with this</a> </li> </ul> </nav> </div> <script type="application/ld+json"> { "@context": "http://schema.org", "@type": "AudioObject", "contentUrl": "https://www.visionlearning.com/img/library/moduleAudio/module_177.mp3", "description": "Recording of Theories, Hypotheses, and Laws : Theories are not based on one scientist's work but on an accumulation of evidence and ideas from many scientists over time. This module discusses how scientific theories are built and revised. It uses the development of the theory of evolution through natural selection to illustrate how theories are built through a process of testing, expanding, and refining.", "encodingFormat": "mp3", "name": "module_177.mp3" } </script> <div class="module_header_audio"> <div class="audio-player border border-radius"> <audio id="audio"> <source src="https://www.visionlearning.com/img/library/moduleAudio/module_177.mp3" type="audio/mpeg"> Your browser does not support the audio element. </audio> <div class="audio-player__title"> <p>Listen to this reading</p> <span class="audio-player__timestamp" id="timestamp"> 00:00 </span> </div> <div class="audio-player__controls" id="controls"> <button class="button button--icon-only" id="play-pause-button"> <span class="icon icon-play" aria-hidden="true"></span> </button> <div class="audio-player__progress" id="progress-bar" tabindex="0" aria-valuemin="0" aria-valuemax="100" aria-valuenow="0" aria-label="Use arrow keys to forward or rewind the audio" role="slider"> <div class="audio-player__progress__fill"> <span class="audio-player__thumb"></span> </div> </div> <div class="audio-player__volume-container"> <button id="mute-button"> <span class="icon icon-volume"></span> </button> <div class="audio-player__volume" tabindex="0" aria-valuemin="0" aria-valuemax="100" aria-valuenow="100" aria-label="Use arrow keys to adjust volume" role="slider"> <div class="audio-player__volume__fill"> <span class="audio-player__thumb"></span> </div> </div> </div> </div> </div> </div> </header> <hr class="divider"/>   <div class="grid grid--sidebar-right grid--divider"> <div class="order-2 order-1--lg module__main"> <div class="narrow margin-x-auto margin-y-5"> <div class="accordion margin-bottom-5">  <button class="accordion__button" id="acc-button-key-concepts" data-accordion="button" aria-controls="acc-panel-key-concepts" aria-expanded="true" tabindex="0"> Did you know? </button> <div class="accordion__panel shown show" id="acc-panel-key-concepts" data-accordion="panel" aria-labelledby="acc-button-key-concepts" role="region"> <div class="accordion__panel__content"> <p>Did you know that the idea of evolution had been part of Western thought for more than 2,000 years before Charles Darwin was born? Like many theories, the theory of evolution was the result of the work of many different scientists working in different disciplines over a period of time.</p> </div> </div>  <button class="accordion__button" id="acc-button-table-of-contents" data-accordion="button" aria-controls="acc-panel-table-of-contents" aria-expanded="false" tabindex="0"> Key concepts </button> <div class="accordion__panel" id="acc-panel-table-of-contents" data-accordion="panel" aria-labelledby="acc-button-table-of-contents" role="region" aria-hidden="true"> <div class="accordion__panel__content"> <ul class="bulleted"> <li><p>A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and is logical, testable, and predictive.</p></li> <li><p>As new evidence comes to light, or new interpretations of existing data are proposed, theories may be revised and even change; however, they are not tenuous or speculative.</p></li> <li><p>A scientific hypothesis is an inferred explanation of an observation or research finding; while more exploratory in nature than a theory, it is based on existing scientific knowledge.</p></li> <li><p>A scientific law is an expression of a mathematical or descriptive relationship observed in nature.</p></li> </ul> </div> </div>  <button class="accordion__button" id="acc-button-terms-you-should-know" data-accordion="button" aria-controls="acc-panel-terms-you-should-know" aria-expanded="false" tabindex="0"> Terms you should know </button> <div class="accordion__panel" id="acc-panel-terms-you-should-know" data-accordion="panel" aria-labelledby="acc-button-terms-you-should-know" role="region" aria-hidden="true"> <div class="accordion__panel__content"> <dl> <dt><a href="/en/glossary/view/data">data </a></dt> <dd> pieces of information collected through observation and measurement </dd> <dt><a href="/en/glossary/view/evidence">evidence </a></dt> <dd> support for an idea, opinion, or hypothesis </dd> <dt><a href="/en/glossary/view/evolution">evolution </a></dt> <dd> genetic change in a plant or animal population over generations</dd> </dl> </div> </div> </div> <hr class="border-color-dark" /> <section> <div class="container narrow"> <p>Imagine yourself shopping in a grocery store with a good friend who happens to be a chemist. Struggling to choose between the many different types of tomatoes in front of you, you pick one up, turn to your friend, and ask her if she thinks the tomato is <mark class="term" data-term="organic" data-term-def="Originating from a living organism; a compound that contains hydrocarbons." data-term-url="/en/glossary/view/organic/8530">organic</mark>. Your friend simply chuckles and replies, "Of course it's organic!" without even looking at how the fruit was grown. Why the amused reaction? Your friend is highlighting a simple difference in vocabulary. To a chemist, the term <em>organic</em> refers to any <mark class="term" data-term="compound" data-term-def="A material formed by the chemical combination of elements in defined proportions. Compounds can be chemically decomposed into simpler substances." data-term-url="/en/glossary/view/compound/1517">compound</mark> in which hydrogen is bonded to carbon. Tomatoes (like all plants) are abundant in organic compounds – thus your friend's laughter. In modern agriculture, however, <em>organic</em> has come to mean food items grown or raised without the use of chemical fertilizers, pesticides, or other additives.</p> <p>So who is correct? You both are. Both uses of the word are correct, though they mean different things in different contexts. There are, of course, lots of words that have more than one meaning (like <em>bat</em>, for example), but multiple meanings can be especially confusing when two meanings convey very different ideas and are specific to one field of study.</p> <p><section id="toc_1" class=""> <h2>Scientific theories</h2></p> <p>The term <em>theory</em> also has two meanings, and this double meaning often leads to confusion. In common language, the term <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark> generally refers to speculation or a hunch or guess. You might have a theory about why your favorite sports team isn't playing well, or who ate the last cookie from the cookie jar. But these <mark class="term" data-term="theory" data-term-url="/en/glossary/view/theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;">theories</mark> do not fit the scientific use of the term. In science, a theory is a well-substantiated and comprehensive set of ideas that explains a phenomenon in nature. A scientific theory is based on large amounts of <mark class="term" data-term="data" data-term-def="(plural form of <b>datum</b>) A collection of pieces of information, generally taking the form of numbers, text, bits, or facts, that&hellip;" data-term-url="/en/glossary/view/data/3729">data</mark> and <mark class="term" data-term="observation" data-term-def="1. The act of noticing something. 2. A record of that which has been noticed." data-term-url="/en/glossary/view/observation/8255">observations</mark> that have been collected over time. Scientific theories can be tested and refined by additional <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark>, and they allow scientists to make predictions. Though you may be correct in your hunch, your cookie jar conjecture doesn't fit this more rigorous definition.</p><p>All scientific disciplines have well-established, fundamental <mark class="term" data-term="theory" data-term-url="/en/glossary/view/theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;">theories</mark>. For example, atomic <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark> describes the nature of <mark class="term" data-term="matter" data-term-def="The substance that makes up physical objects." data-term-url="/en/glossary/view/matter/8264">matter</mark> and is supported by multiple lines of <mark class="term" data-term="evidence" data-term-def="Support for an idea, opinion, or hypothesis." data-term-url="/en/glossary/view/evidence/8243">evidence</mark> from the way substances behave and react in the world around us (see our series on <a href="http://visionlearning.com/en/library/sub/Chemistry/1/Atomic-Theory-and-Structure/9">Atomic Theory</a>). Plate tectonic theory describes the large scale movement of the outer layer of the Earth and is supported by evidence from studies about <mark class="term" data-term="earthquake" data-term-def="1. The sudden motion or slip along a fault. 2. The ground shaking that results from the release of seismic energy&hellip;" data-term-url="/en/glossary/view/earthquake/1664">earthquakes</mark>, magnetic properties of the rocks that make up the <mark class="term" data-term="seafloor" data-term-def="The bottom surface of the ocean." data-term-url="/en/glossary/view/seafloor/8280">seafloor</mark>, and the distribution of volcanoes on Earth (see our series on <a href="http://visionlearning.com/en/library/sub/Earth-Science/6/Plate-Tectonics/21">Plate Tectonic Theory</a>). The theory of <mark class="term" data-term="evolution" data-term-def="Change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift." data-term-url="/en/glossary/view/evolution/5284">evolution</mark> by <mark class="term" data-term="natural selection" data-term-def="The process whereby characteristics that promote survival and reproduction are passed on to future generations, so these characteristics become more frequent&hellip;" data-term-url="/en/glossary/view/natural+selection/11402">natural selection</mark>, which describes the mechanism by which <mark class="term" data-term="inherited" data-term-def="Passed down from one generation to another generation." data-term-url="/en/glossary/view/inherited/8738">inherited</mark> <mark class="term" data-term="trait" data-term-def="A specific characteristic that is genetically determined." data-term-url="/en/glossary/view/trait/8271">traits</mark> that affect survivability or reproductive success can cause changes in living <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark> over <mark class="term" data-term="generation" data-term-def="Offspring at the same step in the line of descent from a common ancestor." data-term-url="/en/glossary/view/generation/8293">generations</mark>, is supported by extensive studies of <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark>, <mark class="term" data-term="fossil" data-term-def="The preserved impression or remains of an animal or plant whose living tissue has been replaced by minerals." data-term-url="/en/glossary/view/fossil/8558">fossils</mark>, and other types of scientific evidence (see our <a href="http://visionlearning.com/en/library/sub/Biology/2/Evolutionary-Biology/65">Charles Darwin series</a> for more information). Each of these major theories guides and informs modern <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark> in those fields, integrating a broad, comprehensive set of ideas.</p><p>So how are these fundamental <mark class="term" data-term="theory" data-term-url="/en/glossary/view/theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;">theories</mark> developed, and why are they considered so well supported? Let's take a closer look at some of the <mark class="term" data-term="data" data-term-def="(plural form of <b>datum</b>) A collection of pieces of information, generally taking the form of numbers, text, bits, or facts, that&hellip;" data-term-url="/en/glossary/view/data/3729">data</mark> and <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark> supporting the <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark> of <mark class="term" data-term="natural selection" data-term-def="The process whereby characteristics that promote survival and reproduction are passed on to future generations, so these characteristics become more frequent&hellip;" data-term-url="/en/glossary/view/natural+selection/11402">natural selection</mark> to better see how a theory develops.</p> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form class="" name="cc5873"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">A theory is simply an educated guess made by a scientist.</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-5873-0-option-a" name="quiz-option-5873" type="radio" value="true" > <span class="option__label"> <span class="screen-reader-only">a.</span> true </span> </label> <span class="quiz__response" id="response-5873-0"> <strong>Incorrect.</strong> </span> </div> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-5873-1-option-b" name="quiz-option-5873" type="radio" value="false" > <span class="option__label"> <span class="screen-reader-only">b.</span> false </span> </label> <span class="quiz__response" id="response-5873-1"> <strong>Correct!</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_2"> <h2>The development of a scientific theory: Evolution and natural selection</h2><p>The <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark> of <mark class="term" data-term="evolution" data-term-def="Change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift." data-term-url="/en/glossary/view/evolution/5284">evolution</mark> by <mark class="term" data-term="natural selection" data-term-def="The process whereby characteristics that promote survival and reproduction are passed on to future generations, so these characteristics become more frequent&hellip;" data-term-url="/en/glossary/view/natural+selection/11402">natural selection</mark> is sometimes maligned as <mark class="term" data-term="Charles Darwin" data-term-def="English naturalist and geologist born in Shrewsbury, Shropshire (1809-1882). While serving as naturalist aboard HMS Beagle, Darwin developed his theory of&hellip;" data-term-url="/en/glossary/view/Darwin%2C+Charles/4507">Charles Darwin</mark>'s speculation on the origin of modern life forms. However, evolutionary theory is not speculation. While Darwin is rightly credited with first articulating the theory of natural selection, his ideas built on more than a century of scientific <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark> that came before him, and are supported by over a century and a half of research since.</p></section> <section id="toc2_1"><h3>The Fixity Notion: Linnaeus</h3> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox="" data-lightbox-src="/img/library/large_images/image_4839.jpg"> <img src="/img/library/modules/mid177/Image/VLObject-4839-091019111003.jpg" alt="Figure 1: Cover of the 1760 edition of Systema Naturae." /> </button> <figcaption> <p><b>Figure 1:</b> Cover of the 1760 edition of <i>Systema Naturae</i>.</p> </figcaption> </figure> </div> <p>Research about the origins and diversity of life proliferated in the 18th and 19th centuries. <mark class="term" data-term="Carolus Linnaeus" data-term-def="(also Carl Linnaeus or Karl von Linné) Swedish physician, naturalist, and taxonomist born in Stenbrohult (1707-1778). Inspired by the work of&hellip;" data-term-url="/en/glossary/view/Linnaeus%2C+Carolus/4511">Carolus Linnaeus</mark>, a Swedish botanist and the father of modern <mark class="term" data-term="taxonomy" data-term-def="The basis, procedures, and rules for naming and classifying organisms." data-term-url="/en/glossary/view/taxonomy/894">taxonomy</mark> (see our module <a href="http://visionlearning.com/library/module_viewer.php?mid=70&l=">Taxonomy I</a> for more information), was a devout Christian who believed in the concept of <mark class="term" data-term="Fixity of Species" data-term-def="An idea popular among 16th and 17th century European zoologists and botanists that reflected Western religion and the story of creation&hellip;" data-term-url="/en/glossary/view/Fixity+of+Species/4763">Fixity of Species</mark>, an idea based on the biblical story of creation. The Fixity of <mark class="term" data-term="species" data-term-def="1. In biological classifications, it is the lowest and most basic unit of the Linnaean taxonomic hierarchy (although it is also&hellip;" data-term-url="/en/glossary/view/species/893">Species</mark> concept said that each species is based on an ideal form that has not changed over time. In the early stages of his career, Linnaeus traveled extensively and collected <mark class="term" data-term="data" data-term-def="(plural form of <b>datum</b>) A collection of pieces of information, generally taking the form of numbers, text, bits, or facts, that&hellip;" data-term-url="/en/glossary/view/data/3729">data</mark> on the structural similarities and differences between different species of plants. Noting that some very different plants had similar structures, he began to piece together his landmark work, <em>Systema Naturae,</em> in 1735 (Figure 1). In <em>Systema</em>, Linnaeus classified <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark> into related groups based on similarities in their physical features. He developed a hierarchical <mark class="term" data-term="classification" data-term-def="In biology, the arranging of groups of organisms into sets or divisions on the basis of their evolutionary relationships." data-term-url="/en/glossary/view/classification/879">classification</mark> <mark class="term" data-term="system" data-term-def="A group of interacting, interrelated or interdependent components that form a complex whole. The size of the system is defined for&hellip;" data-term-url="/en/glossary/view/system/3904">system</mark>, even drawing relationships between seemingly disparate species (for example, humans, orangutans, and chimpanzees) based on the physical similarities that he observed between these organisms. Linnaeus did not explicitly discuss change in organisms or propose a reason for his hierarchy, but by grouping organisms based on physical characteristics, he suggested that species are related, unintentionally challenging the Fixity notion that each species is created in a unique, ideal form.</p></section> <section id="toc2_2"><h3>The age of Earth: Leclerc and Hutton</h3><p>Also in the early 1700s, Georges-Louis Leclerc, a French naturalist, and <mark class="term" data-term="James Hutton" data-term-def="Scottish geologist, chemist, and naturalist born in Edinburgh (1726-1797). Hutton is considered to be the father of modern geology. From his&hellip;" data-term-url="/en/glossary/view/Hutton%2C+James/4534">James Hutton</mark>, a Scottish geologist, began to develop new ideas about the age of the Earth. At the time, many people thought of the Earth as 6,000 years old, based on a strict <mark class="term" data-term="interpretation" data-term-def="An explanation of patterns observed in the data." data-term-url="/en/glossary/view/interpretation/8235">interpretation</mark> of the events detailed in the Christian Old Testament by the influential Scottish Archbishop Ussher. By observing other planets and comets in the solar <mark class="term" data-term="system" data-term-def="A group of interacting, interrelated or interdependent components that form a complex whole. The size of the system is defined for&hellip;" data-term-url="/en/glossary/view/system/3904">system</mark>, Leclerc hypothesized that Earth began as a hot, fiery ball of molten rock, mostly consisting of iron. Using the cooling rate of iron, Leclerc calculated that Earth must therefore be at least 70,000 years old in order to have reached its present temperature. </p><p>Hutton approached the same topic from a different perspective, gathering <mark class="term" data-term="observation" data-term-def="1. The act of noticing something. 2. A record of that which has been noticed." data-term-url="/en/glossary/view/observation/8255">observations</mark> of the relationships between different rock formations and the rates of modern geological processes near his home in Scotland. He recognized that the relatively slow processes of <mark class="term" data-term="erosion" data-term-def="The action or process of eroding: wearing away by the action of water, wind, glacial ice, etc." data-term-url="/en/glossary/view/erosion/2193">erosion</mark> and sedimentation could not create all of the exposed rock layers in only a few thousand years (see our module <a href="http://visionlearning.com/library/module_viewer.php?mid=128&l=">The Rock Cycle</a>). Based on his extensive collection of <mark class="term" data-term="data" data-term-def="(plural form of <b>datum</b>) A collection of pieces of information, generally taking the form of numbers, text, bits, or facts, that&hellip;" data-term-url="/en/glossary/view/data/3729">data</mark> (just one of his many publications ran to 2,138 pages), Hutton suggested that the Earth was far older than human history – hundreds of millions of years old. </p><p>While we now know that both Leclerc and Hutton significantly underestimated the age of the Earth (by about 4 billion years), their <mark class="term" data-term="work" data-term-def="A process that occurs when a force acts over a distance, as when an object is moved. Work equals the multiple&hellip;" data-term-url="/en/glossary/view/work/1502">work</mark> shattered long-held beliefs and opened a window into <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark> on how life can change over these very long timescales.</p></section> <section id="toc2_3"><h3>Fossil studies lead to the development of a theory of evolution: Cuvier</h3> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox="" data-lightbox-src="/img/library/large_images/image_4840.jpg"> <img src="/img/library/modules/mid177/Image/VLObject-4840-091019111018.jpg" alt="Figure 2: Illustration of an Indian elephant jaw and a mammoth jaw from Cuvier's 1796 paper." /> </button> <figcaption> <p><b>Figure 2:</b> Illustration of an Indian elephant jaw and a mammoth jaw from Cuvier's 1796 paper.</p> </figcaption> </figure> </div> <p>With the age of Earth now extended by Leclerc and Hutton, more researchers began to turn their attention to studying past life. <mark class="term" data-term="fossil" data-term-def="The preserved impression or remains of an animal or plant whose living tissue has been replaced by minerals." data-term-url="/en/glossary/view/fossil/8558">Fossils</mark> are the main way to study past life forms, and several key studies on fossils helped in the development of a <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark> of <mark class="term" data-term="evolution" data-term-def="Change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift." data-term-url="/en/glossary/view/evolution/5284">evolution</mark>. In 1795, Georges Cuvier began to work at the National Museum in Paris as a naturalist and anatomist. Through his work, Cuvier became interested in fossils found near Paris, which some claimed were the remains of the elephants that Hannibal rode over the Alps when he invaded Rome in 218 <mark class="term" data-term="BCE" data-term-def="An abbreviation for Before the Common Era, which is a designation for the years prior to year 1 of the Gregorian&hellip;" data-term-url="/en/glossary/view/BCE/3720">BCE</mark>. In studying both the fossils and living <mark class="term" data-term="species" data-term-def="1. In biological classifications, it is the lowest and most basic unit of the Linnaean taxonomic hierarchy (although it is also&hellip;" data-term-url="/en/glossary/view/species/893">species</mark>, Cuvier documented different patterns in the dental structure and number of teeth between the fossils and modern elephants (Figure 2) (Horner, 1843). Based on these <mark class="term" data-term="data" data-term-def="(plural form of <b>datum</b>) A collection of pieces of information, generally taking the form of numbers, text, bits, or facts, that&hellip;" data-term-url="/en/glossary/view/data/3729">data</mark>, Cuvier hypothesized that the fossil remains were not left by Hannibal, but were from a distinct species of animal that once roamed through Europe and had gone <mark class="term" data-term="extinction" data-term-url="/en/glossary/view/extinction" data-term-def="The complete and permanent loss of all individuals of a species of organism.">extinct</mark> thousands of years earlier: the mammoth. The concept of species <mark class="term" data-term="extinction" data-term-def="The complete and permanent loss of all individuals of a species of organism." data-term-url="/en/glossary/view/extinction/5615">extinction</mark> had been discussed by a few individuals before Cuvier, but it was in direct opposition to the <mark class="term" data-term="Fixity of Species" data-term-def="An idea popular among 16th and 17th century European zoologists and botanists that reflected Western religion and the story of creation&hellip;" data-term-url="/en/glossary/view/Fixity+of+Species/4763">Fixity of Species</mark> concept – if every <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organism</mark> were based on a perfectly adapted, ideal form, how could any cease to exist? That would suggest it was no longer ideal.</p><p>While his work provided critical <mark class="term" data-term="evidence" data-term-def="Support for an idea, opinion, or hypothesis." data-term-url="/en/glossary/view/evidence/8243">evidence</mark> of <mark class="term" data-term="extinction" data-term-def="The complete and permanent loss of all individuals of a species of organism." data-term-url="/en/glossary/view/extinction/5615">extinction</mark>, a key component of <mark class="term" data-term="evolution" data-term-def="Change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift." data-term-url="/en/glossary/view/evolution/5284">evolution</mark>, Cuvier was highly critical of the idea that <mark class="term" data-term="species" data-term-def="1. In biological classifications, it is the lowest and most basic unit of the Linnaean taxonomic hierarchy (although it is also&hellip;" data-term-url="/en/glossary/view/species/893">species</mark> could change over time. As a result of his extensive studies of animal anatomy, Cuvier had developed a holistic view of <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark>, stating that the</p><blockquote class="blockquote"> <p>number, direction, and shape of the bones that compose each part of an animal's body are always in a necessary relation to all the other parts, in such a way that ... one can infer the whole from any one of them ...</p> </p></blockquote><p>In other words, Cuvier viewed each part of an <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organism</mark> as a unique, essential component of the whole organism. If one part were to change, he believed, the organism could not survive. His skepticism about the ability of organisms to change led him to criticize the whole idea of <mark class="term" data-term="evolution" data-term-def="Change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift." data-term-url="/en/glossary/view/evolution/5284">evolution</mark>, and his prominence in France as a scientist played a large role in discouraging the acceptance of the idea in the scientific community.</p></section> <section id="toc2_4"><h3>Studies of invertebrates support a theory of change in species: Lamarck</h3><p>Jean Baptiste Lamarck, a contemporary of Cuvier's at the National Museum in Paris, studied <mark class="term" data-term="invertebrate" data-term-def="An organism without a backbone. Invertebrates account for 95-99% of all animal species on Earth and include organisms like worms, insects,&hellip;" data-term-url="/en/glossary/view/invertebrate/5270">invertebrates</mark> like insects and worms. As Lamarck worked through the museum's large collection of invertebrates, he was impressed by the number and variety of <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark>. He became convinced that organisms could, in fact, change through time, stating that </p><blockquote class="blockquote"> <p>... time and favorable conditions are the two principal means which nature has employed in giving existence to all her productions. We know that for her time has no limit, and that consequently she always has it at her disposal.</p> </p></blockquote><p>This was a radical departure from both the fixity concept and Cuvier's ideas, and it built on the long timescale that geologists had recently established. Lamarck proposed that changes that occurred during an <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organism</mark>'s lifetime could be passed on to their offspring, suggesting, for example, that a body builder's muscles would be <mark class="term" data-term="inherited" data-term-def="Passed down from one generation to another generation." data-term-url="/en/glossary/view/inherited/8738">inherited</mark> by their children. </p><p>As it turned out, the mechanism by which Lamarck proposed that <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark> change over time was wrong, and he is now often referred to disparagingly for his "inheritance of acquired characteristics" idea. Yet despite the fact that some of his ideas were discredited, Lamarck established a support for evolutionary <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark> that others would build on and improve.</p> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form class="" name="cc5886"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">To develop theories, scientists most often</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-5886-0-option-a" name="quiz-option-5886" type="radio" value="rely on an accumulation of knowledge developed by many scientists over time." > <span class="option__label"> <span class="screen-reader-only">a.</span> rely on an accumulation of knowledge developed by many scientists over time. </span> </label> <span class="quiz__response" id="response-5886-0"> <strong>Correct!</strong> </span> </div> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-5886-1-option-b" name="quiz-option-5886" type="radio" value="use only their own direct experience and observations." > <span class="option__label"> <span class="screen-reader-only">b.</span> use only their own direct experience and observations. </span> </label> <span class="quiz__response" id="response-5886-1"> <strong>Incorrect.</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc2_5"><h3>Rock layers as evidence for evolution: Smith</h3><p>In the early 1800s, a British geologist and canal surveyor named William Smith added another component to the accumulating <mark class="term" data-term="evidence" data-term-def="Support for an idea, opinion, or hypothesis." data-term-url="/en/glossary/view/evidence/8243">evidence</mark> for <mark class="term" data-term="evolution" data-term-def="Change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift." data-term-url="/en/glossary/view/evolution/5284">evolution</mark>. Smith observed that rock layers exposed in different parts of England bore similarities to one another: These layers (or strata) were arranged in a predictable order, and each layer contained distinct groups of <mark class="term" data-term="fossil" data-term-def="The preserved impression or remains of an animal or plant whose living tissue has been replaced by minerals." data-term-url="/en/glossary/view/fossil/8558">fossils</mark>. From this series of <mark class="term" data-term="observation" data-term-def="1. The act of noticing something. 2. A record of that which has been noticed." data-term-url="/en/glossary/view/observation/8255">observations</mark>, he developed a <mark class="term" data-term="hypothesis" data-term-def="From the Greek word <em>hypothesis</em> meaning assumption or the basis of an argument, a hypothesis is a proposal intended to explain&hellip;" data-term-url="/en/glossary/view/hypothesis/3727">hypothesis</mark> that specific groups of animals followed one another in a definite sequence through Earth's history, and this sequence could be seen in the rock layers. Smith's hypothesis was based on his knowledge of geological <mark class="term" data-term="principle" data-term-def="In the sciences, a principle is a fundamental, primary, or general law or truth. For instance, one of the most basic&hellip;" data-term-url="/en/glossary/view/principle/5289">principles</mark>, including the <mark class="term" data-term="law" data-term-def="In science, a principle that describes a phenomenon, often mathematically." data-term-url="/en/glossary/view/law/8686">Law</mark> of Superposition.</p><p>The <mark class="term" data-term="law" data-term-def="In science, a principle that describes a phenomenon, often mathematically." data-term-url="/en/glossary/view/law/8686">Law</mark> of Superposition states that <mark class="term" data-term="sediment" data-term-def="Loose, unconsolidated material of the following compositions: <br> 1. rock fragments (also called clasts) transported by wind, moving water,&hellip;" data-term-url="/en/glossary/view/sediment/3310">sediments</mark> are deposited in a time sequence, with the oldest sediments deposited first, or at the bottom, and newer layers deposited on top. The concept was first expressed by the Persian scientist Avicenna in the 11th century, but was popularized by the Danish scientist Nicolas Steno in the 17th century. Note that the law does not state how sediments are deposited; it simply describes the relationship between the ages of deposited sediments.</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox="" data-lightbox-src="/img/library/large_images/image_4841.jpg"> <img src="/img/library/modules/mid177/Image/VLObject-4841-091019111026.jpg" alt="Figure 3: Engraving from William Smith's 1815 monograph on identifying strata by fossils." /> </button> <figcaption> <p><b>Figure 3:</b> Engraving from William Smith's 1815 monograph on identifying strata by fossils.</p> </figcaption> </figure> </div> <p>Smith backed up his <mark class="term" data-term="hypothesis" data-term-def="From the Greek word <em>hypothesis</em> meaning assumption or the basis of an argument, a hypothesis is a proposal intended to explain&hellip;" data-term-url="/en/glossary/view/hypothesis/3727">hypothesis</mark> with extensive drawings of <mark class="term" data-term="fossil" data-term-def="The preserved impression or remains of an animal or plant whose living tissue has been replaced by minerals." data-term-url="/en/glossary/view/fossil/8558">fossils</mark> uncovered during his <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark> (Figure 3), thus allowing other scientists to confirm or dispute his findings. His hypothesis has, in fact, been confirmed by many other scientists and has come to be referred to as the <mark class="term" data-term="law" data-term-def="In science, a principle that describes a phenomenon, often mathematically." data-term-url="/en/glossary/view/law/8686">Law</mark> of Faunal Succession. His work was critical to the formation of evolutionary <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark> as it not only confirmed Cuvier's work that <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark> have gone <mark class="term" data-term="extinction" data-term-url="/en/glossary/view/extinction" data-term-def="The complete and permanent loss of all individuals of a species of organism.">extinct</mark>, but it also showed that the appearance of life does not date to the birth of the planet. Instead, the <mark class="term" data-term="fossil record" data-term-def="Collectively, the set of fossilized remains preserved in Earth’s crust that tell the history of Earth, including how and when rocks&hellip;" data-term-url="/en/glossary/view/fossil+record/8942">fossil record</mark> preserves a timeline of the appearance and disappearance of different organisms in the past, and in doing so offers <mark class="term" data-term="evidence" data-term-def="Support for an idea, opinion, or hypothesis." data-term-url="/en/glossary/view/evidence/8243">evidence</mark> for change in organisms over time.</p></section> <section id="toc2_6"><h3>The <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark> of <mark class="term" data-term="evolution" data-term-def="Change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift." data-term-url="/en/glossary/view/evolution/5284">evolution</mark> by natural selection: Darwin and Wallace</h3><p>It was into this world that <mark class="term" data-term="Charles Darwin" data-term-def="English naturalist and geologist born in Shrewsbury, Shropshire (1809-1882). While serving as naturalist aboard HMS Beagle, Darwin developed his theory of&hellip;" data-term-url="/en/glossary/view/Darwin%2C+Charles/4507">Charles Darwin</mark> entered: Linnaeus had developed a <mark class="term" data-term="taxonomy" data-term-def="The basis, procedures, and rules for naming and classifying organisms." data-term-url="/en/glossary/view/taxonomy/894">taxonomy</mark> of <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark> based on their physical relationships, Leclerc and Hutton demonstrated that there was sufficient time in Earth's history for organisms to change, Cuvier showed that <mark class="term" data-term="species" data-term-def="1. In biological classifications, it is the lowest and most basic unit of the Linnaean taxonomic hierarchy (although it is also&hellip;" data-term-url="/en/glossary/view/species/893">species</mark> of organisms have gone <mark class="term" data-term="extinction" data-term-url="/en/glossary/view/extinction" data-term-def="The complete and permanent loss of all individuals of a species of organism.">extinct</mark>, Lamarck proposed that organisms change over time, and Smith established a timeline of the appearance and disappearance of different organisms in the geological <mark class="term" data-term="record" data-term-def="A written account or description. <br> <b>[verb]</b> To write an account or description." data-term-url="/en/glossary/view/record/8239">record</mark>.</p> <div class="figure"> <figure> <button class="lightbox-button lightbox-button--icon" data-lightbox="" data-lightbox-src="/img/library/large_images/image_4842.jpg"> <img src="/img/library/modules/mid177/Image/VLObject-4842-091019111029.jpg" alt="Figure 4: Title page of the 1859 Murray edition of the Origin of Species by Charles Darwin." /> </button> <figcaption> <p><b>Figure 4:</b> Title page of the 1859 Murray edition of the <i>Origin of Species</i> by Charles Darwin.</p> </figcaption> </figure> </div> <p>Charles Darwin collected <mark class="term" data-term="data" data-term-def="(plural form of <b>datum</b>) A collection of pieces of information, generally taking the form of numbers, text, bits, or facts, that&hellip;" data-term-url="/en/glossary/view/data/3729">data</mark> during his work as a naturalist on the <em>HMS Beagle</em> starting in 1831. He took extensive notes on the geology of the places he visited; he made a major find of <mark class="term" data-term="fossil" data-term-def="The preserved impression or remains of an animal or plant whose living tissue has been replaced by minerals." data-term-url="/en/glossary/view/fossil/8558">fossils</mark> of <mark class="term" data-term="extinction" data-term-url="/en/glossary/view/extinction" data-term-def="The complete and permanent loss of all individuals of a species of organism.">extinct</mark> animals in Patagonia and identified an extinct giant ground sloth named <em>Megatherium</em>. He experienced an <mark class="term" data-term="earthquake" data-term-def="1. The sudden motion or slip along a fault. 2. The ground shaking that results from the release of seismic energy&hellip;" data-term-url="/en/glossary/view/earthquake/1664">earthquake</mark> in Chile that stranded beds of living mussels above water, where they would be preserved for years to come. </p><p>Perhaps most famously, he conducted extensive studies of animals on the Galápagos Islands, noting subtle differences in <mark class="term" data-term="species" data-term-def="1. In biological classifications, it is the lowest and most basic unit of the Linnaean taxonomic hierarchy (although it is also&hellip;" data-term-url="/en/glossary/view/species/893">species</mark> of mockingbird, tortoise, and finch that were isolated on different islands with different environmental conditions. These subtle differences made the animals highly adapted to their <mark class="term" data-term="environment" data-term-def="The conditions that surround and affect an organism." data-term-url="/en/glossary/view/environment/8270">environments</mark>.</p><p>This broad <mark class="term" data-term="spectrum" data-term-def="(plural: <b>spectra</b>) A continuing range such as of color or frequency; a series of colors arranged by wavelength as in a rainbow." data-term-url="/en/glossary/view/spectrum/8261">spectrum</mark> of <mark class="term" data-term="data" data-term-def="(plural form of <b>datum</b>) A collection of pieces of information, generally taking the form of numbers, text, bits, or facts, that&hellip;" data-term-url="/en/glossary/view/data/3729">data</mark> led Darwin to propose an idea about how <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark> change "by means of natural selection" (Figure 4). But this idea was not based only on his work, it was also based on the accumulation of <mark class="term" data-term="evidence" data-term-def="Support for an idea, opinion, or hypothesis." data-term-url="/en/glossary/view/evidence/8243">evidence</mark> and ideas of many others before him. Because his proposal encompassed and explained many different lines of evidence and previous work, they formed the basis of a new and robust scientific <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark> regarding change in organisms – the theory of <mark class="term" data-term="evolution" data-term-def="Change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift." data-term-url="/en/glossary/view/evolution/5284">evolution</mark> by <mark class="term" data-term="natural selection" data-term-def="The process whereby characteristics that promote survival and reproduction are passed on to future generations, so these characteristics become more frequent&hellip;" data-term-url="/en/glossary/view/natural+selection/11402">natural selection</mark>.</p><p>Darwin's ideas were grounded in <mark class="term" data-term="evidence" data-term-def="Support for an idea, opinion, or hypothesis." data-term-url="/en/glossary/view/evidence/8243">evidence</mark> and <mark class="term" data-term="data" data-term-def="(plural form of <b>datum</b>) A collection of pieces of information, generally taking the form of numbers, text, bits, or facts, that&hellip;" data-term-url="/en/glossary/view/data/3729">data</mark> so compelling that if he had not conceived them, someone else would have. In fact, someone else did. Between 1858 and 1859, <mark class="term" data-term="Alfred Russel Wallace" data-term-def="English naturalist, geographer, and anthropologist, born in Monmouthshire (1823-1913). Wallace's most important work was in the Malay Archipelago (now the Indonesian&hellip;" data-term-url="/en/glossary/view/Wallace%2C+Alfred+Russel/4508">Alfred Russel Wallace</mark>, a British naturalist, wrote a series of letters to Darwin that independently proposed <mark class="term" data-term="natural selection" data-term-def="The process whereby characteristics that promote survival and reproduction are passed on to future generations, so these characteristics become more frequent&hellip;" data-term-url="/en/glossary/view/natural+selection/11402">natural selection</mark> as the means for evolutionary change. The letters were presented to the Linnean <mark class="term" data-term="society" data-term-def="A group of people who belong to an organization that has been formed because of shared interest in a specific field." data-term-url="/en/glossary/view/society/8249">Society</mark> of London, a prominent scientific society at the time (see our module on <a href="/library/module_viewer.php?mid=162">Scientific Institutions and Societies</a>). This long chain of <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark> highlights that <mark class="term" data-term="theory" data-term-url="/en/glossary/view/theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;">theories</mark> are not just the work of one individual. At the same time, however, it often takes the insight and creativity of individuals to put together all of the pieces and propose a new <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark>. Both Darwin and Wallace were experienced naturalists who were familiar with the work of others. While all of the work leading up to 1830 contributed to the theory of <mark class="term" data-term="evolution" data-term-def="Change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift." data-term-url="/en/glossary/view/evolution/5284">evolution</mark>, Darwin's and Wallace's theory changed the way that future research was focused by presenting a comprehensive, well-substantiated set of ideas, thus becoming a fundamental theory of biological research.</p></section> <section id="toc_3"> <h2>Expanding, testing, and refining scientific theories</h2></section> <section id="toc2_7"><h3>Genetics and evolution: Mendel and Dobzhansky</h3><p>Since Darwin and Wallace first published their ideas, extensive <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark> has tested and expanded the <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark> of <mark class="term" data-term="evolution" data-term-def="Change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift." data-term-url="/en/glossary/view/evolution/5284">evolution</mark> by <mark class="term" data-term="natural selection" data-term-def="The process whereby characteristics that promote survival and reproduction are passed on to future generations, so these characteristics become more frequent&hellip;" data-term-url="/en/glossary/view/natural+selection/11402">natural selection</mark>. Darwin had no concept of <mark class="term" data-term="gene" data-term-def="Material (usually DNA) that is inherited from a parent and which encodes for a cellular component important for some cellular function." data-term-url="/en/glossary/view/gene/3294">genes</mark> or <mark class="term" data-term="DNA" data-term-def="Deoxyribonucleic acid. A double-stranded nucleic acid containing the sugar 2-deoxy-D-ribose. A constituent of cellular nuclear material responsible for encoding&hellip;" data-term-url="/en/glossary/view/DNA/1604">DNA</mark> or the mechanism by which characteristics were <mark class="term" data-term="inherited" data-term-def="Passed down from one generation to another generation." data-term-url="/en/glossary/view/inherited/8738">inherited</mark> within a <mark class="term" data-term="species" data-term-def="1. In biological classifications, it is the lowest and most basic unit of the Linnaean taxonomic hierarchy (although it is also&hellip;" data-term-url="/en/glossary/view/species/893">species</mark>. A contemporary of Darwin's, the Austrian monk <mark class="term" data-term="Gregor Mendel" data-term-def="Austrian Augustinian monk and scientist born in Heizendorf (now Hynice, Chech Republic) (1822-1884). In 1865, Mendel wrote <i>Versuche über Pflanzen-Hybride (Treatises&hellip;" data-term-url="/en/glossary/view/Mendel%2C+Gregor/4509">Gregor Mendel</mark>, first presented his own landmark study, <em>Experiments in Plant Hybridization,</em> in 1865 in which he provided the basic patterns of genetic <mark class="term" data-term="inheritance" data-term-def="The transmission of genetic traits from parent to offspring." data-term-url="/en/glossary/view/inheritance/8294">inheritance</mark>, describing which characteristics (and evolutionary changes) can be passed on in <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark> (see our <a href="http://visionlearning.com/library/module_viewer.php?mid=129&l=">Genetics I module</a> for more information). Still, it wasn't until much later that a "gene" was defined as the heritable unit. </p><p>In 1937, the Ukrainian born geneticist Theodosius Dobzhansky published <em>Genetics and the Origin of Species</em>, a seminal work in which he described <mark class="term" data-term="gene" data-term-def="Material (usually DNA) that is inherited from a parent and which encodes for a cellular component important for some cellular function." data-term-url="/en/glossary/view/gene/3294">genes</mark> themselves and demonstrated that it is through <mark class="term" data-term="mutation" data-term-def="A change in gene sequences of cell DNA." data-term-url="/en/glossary/view/mutation/8757">mutations</mark> in genes that change occurs. The work defined <mark class="term" data-term="evolution" data-term-def="Change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift." data-term-url="/en/glossary/view/evolution/5284">evolution</mark> as "a change in the frequency of an <mark class="term" data-term="allele" data-term-def="A variation of a genetic element, usually resulting in a distinct trait." data-term-url="/en/glossary/view/allele/3302">allele</mark> within a gene pool" (<a href="#refs" onClick="open_refs();">Dobzhansky, 1982</a>). These studies and others in the field of genetics have added to Darwin's work, expanding the scope of the <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark>.</p></section> <section id="toc2_8"><h3>Evolution under a microscope: Lenski</h3><p>More recently, Dr. Richard Lenski, a scientist at Michigan State University, isolated a single <em>Escherichia coli</em> bacterium in 1989 as the first step of the longest running experimental test of evolutionary <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark> to date – a true test meant to replicate <mark class="term" data-term="evolution" data-term-def="Change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift." data-term-url="/en/glossary/view/evolution/5284">evolution</mark> and <mark class="term" data-term="natural selection" data-term-def="The process whereby characteristics that promote survival and reproduction are passed on to future generations, so these characteristics become more frequent&hellip;" data-term-url="/en/glossary/view/natural+selection/11402">natural selection</mark> in the lab. </p><p>After the single microbe had multiplied, Lenski isolated the offspring into 12 different <mark class="term" data-term="strain" data-term-def="A group of closely related organisms; a distinct variety, as in a strain of bacteria." data-term-url="/en/glossary/view/strain/8288">strains</mark>, each in their own glucose-supplied culture, predicting that the genetic make-up of each strain would change over time to become more adapted to their specific culture as predicted by evolutionary <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark>. These 12 lines have been nurtured for over 40,000 bacterial <mark class="term" data-term="generation" data-term-def="Offspring at the same step in the line of descent from a common ancestor." data-term-url="/en/glossary/view/generation/8293">generations</mark> (luckily bacterial generations are much shorter than human generations) and exposed to different selective pressures such as <mark class="term" data-term="heat" data-term-def="A measure of the total internal energy of a substance that can be increased or decreased when objects with different temperatures&hellip;" data-term-url="/en/glossary/view/heat/1506">heat</mark>, cold, antibiotics, and infection with other microorganisms. Lenski and colleagues have studied dozens of aspects of evolutionary theory with these genetically isolated <mark class="term" data-term="population" data-term-def="In biology, the population is all individuals of a certain kind of plant or animal that live in a particular habitat.&hellip;" data-term-url="/en/glossary/view/population/8283">populations</mark>. In 1999, they published a paper that demonstrated that random genetic <mark class="term" data-term="mutation" data-term-def="A change in gene sequences of cell DNA." data-term-url="/en/glossary/view/mutation/8757">mutations</mark> were common within the populations and highly diverse across different individual <mark class="term" data-term="bacteria" data-term-def="(plural of bacterium) A large group of one-celled organisms that are found almost everywhere." data-term-url="/en/glossary/view/bacteria/8679">bacteria</mark>. However, "pivotal" mutations that are associated with beneficial changes in the group are shared by all descendants in a population and are much rarer than random mutations, as predicted by the theory of <mark class="term" data-term="evolution" data-term-def="Change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift." data-term-url="/en/glossary/view/evolution/5284">evolution</mark> by <mark class="term" data-term="natural selection" data-term-def="The process whereby characteristics that promote survival and reproduction are passed on to future generations, so these characteristics become more frequent&hellip;" data-term-url="/en/glossary/view/natural+selection/11402">natural selection</mark> (Papadopoulos et al., 1999).</p></section> <section id="toc2_9"><h3>Punctuated equilibrium: Gould and Eldredge</h3><p>While established scientific <mark class="term" data-term="theory" data-term-url="/en/glossary/view/theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;">theories</mark> like <mark class="term" data-term="evolution" data-term-def="Change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift." data-term-url="/en/glossary/view/evolution/5284">evolution</mark> have a wealth of <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark> and <mark class="term" data-term="evidence" data-term-def="Support for an idea, opinion, or hypothesis." data-term-url="/en/glossary/view/evidence/8243">evidence</mark> supporting them, this does not mean that they cannot be refined as new information or new perspectives on existing <mark class="term" data-term="data" data-term-def="(plural form of <b>datum</b>) A collection of pieces of information, generally taking the form of numbers, text, bits, or facts, that&hellip;" data-term-url="/en/glossary/view/data/3729">data</mark> become available. For example, in 1972, biologist <mark class="term" data-term="Stephen Jay Gould" data-term-def="American paleontologist born in New York City, New York (1941-2002). With Niles Eldridge, he co-created and championed the concept of evolution&hellip;" data-term-url="/en/glossary/view/Gould%2C+Stephen+Jay/4498">Stephen Jay Gould</mark> and paleontologist Niles Eldredge took a fresh look at the existing data regarding the timing by which evolutionary change takes place. Gould and Eldredge did not set out to challenge the <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark> of evolution; rather they used it as a guiding <mark class="term" data-term="principle" data-term-def="In the sciences, a principle is a fundamental, primary, or general law or truth. For instance, one of the most basic&hellip;" data-term-url="/en/glossary/view/principle/5289">principle</mark> and asked more specific questions to add detail and nuance to the theory. This is true of all theories in science: they provide a framework for additional research. At the time, many biologists viewed evolution as occurring gradually, causing small incremental changes in <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark> at a relatively steady rate. The idea is referred to as <em>phyletic gradualism</em>, and is rooted in the geological concept of <mark class="term" data-term="uniformitarianism" data-term-def="The fundamental geological principle that the processes that are operating now to shape the world around us have been operating throughout&hellip;" data-term-url="/en/glossary/view/uniformitarianism/3305">uniformitarianism</mark>. After reexamining the available data, Gould and Eldredge came to a different explanation, suggesting that evolution consists of long periods of stability that are punctuated by occasional instances of dramatic change – a <mark class="term" data-term="process" data-term-def="Method, procedure; series of actions or steps." data-term-url="/en/glossary/view/process/8256">process</mark> they called <em>punctuated equilibrium</em>.</p><p>Like Darwin before them, their proposal is rooted in <mark class="term" data-term="evidence" data-term-def="Support for an idea, opinion, or hypothesis." data-term-url="/en/glossary/view/evidence/8243">evidence</mark> and <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark> on evolutionary change, and has been supported by multiple lines of evidence. In fact, punctuated <mark class="term" data-term="equilibrium" data-term-def="A state of balance between opposing forces; a state of balance in which opposing forces cancel one another. A state in&hellip;" data-term-url="/en/glossary/view/equilibrium/8680">equilibrium</mark> is now considered its own <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark> in evolutionary biology. Punctuated equilibrium is not as broad of a theory as <mark class="term" data-term="natural selection" data-term-def="The process whereby characteristics that promote survival and reproduction are passed on to future generations, so these characteristics become more frequent&hellip;" data-term-url="/en/glossary/view/natural+selection/11402">natural selection</mark>. In science, some <mark class="term" data-term="theory" data-term-url="/en/glossary/view/theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;">theories</mark> are broad and overarching of many concepts, such as the theory of <mark class="term" data-term="evolution" data-term-def="Change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift." data-term-url="/en/glossary/view/evolution/5284">evolution</mark> by natural selection; others focus on concepts at a smaller, or more targeted, scale such as punctuated equilibrium. And punctuated equilibrium does not challenge or weaken the concept of natural selection; rather, it represents a change in our understanding of the timing by which change occurs in <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark>, and a theory within a theory. The theory of evolution by natural selection now includes both gradualism and punctuated equilibrium to describe the rate at which change proceeds.</p> <div class="comprehension-checkpoint margin-y-4"> <h6 class="comprehension-checkpoint__header"> <span> <span class="icon icon-question"></span> </span> Comprehension Checkpoint </h6> <form class="" name="cc5895"> <div class="form-entry"> <div class="form-entry__field"> <span class="form-entry__field__label">Observation and research can challenge existing ideas in science.</span> <div class="form-entry__option"> <div class="form-entry__option__radio" data-answer="correct"> <label> <input id="q1-5895-0-option-a" name="quiz-option-5895" type="radio" value="true" > <span class="option__label"> <span class="screen-reader-only">a.</span> true </span> </label> <span class="quiz__response" id="response-5895-0"> <strong>Correct!</strong> </span> </div> <div class="form-entry__option__radio" data-answer="incorrect"> <label> <input id="q1-5895-1-option-b" name="quiz-option-5895" type="radio" value="false" > <span class="option__label"> <span class="screen-reader-only">b.</span> false </span> </label> <span class="quiz__response" id="response-5895-1"> <strong>Incorrect.</strong> </span> </div> </div> </div> </div> </form> </div> </section> <section id="toc_4"> <h2>Hypotheses and laws: Other scientific concepts</h2><p>One of the challenges in understanding scientific terms like <em>theory</em> is that there is not a precise definition even within the scientific community. Some scientists <mark class="term" data-term="debate" data-term-def="A reasoned discussion of opposing points in an argument." data-term-url="/en/glossary/view/debate/8242">debate</mark> over whether certain proposals merit designation as a <mark class="term" data-term="hypothesis" data-term-def="From the Greek word <em>hypothesis</em> meaning assumption or the basis of an argument, a hypothesis is a proposal intended to explain&hellip;" data-term-url="/en/glossary/view/hypothesis/3727">hypothesis</mark> or <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark>, and others mistakenly use the terms interchangeably. But there are differences in these terms. A hypothesis is a proposed explanation for an observable phenomenon. <mark class="term" data-term="hypothesis" data-term-url="/en/glossary/view/hypothesis" data-term-def="From the Greek word <em>hypothesis</em> meaning assumption or the basis of an argument, a hypothesis is a proposal intended to explain&hellip;">Hypotheses</mark>, just like <mark class="term" data-term="theory" data-term-url="/en/glossary/view/theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;">theories</mark>, are based on <mark class="term" data-term="observation" data-term-def="1. The act of noticing something. 2. A record of that which has been noticed." data-term-url="/en/glossary/view/observation/8255">observations</mark> from <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark>. For example, LeClerc did not hypothesize that Earth had cooled from a molten ball of iron as a random guess; rather, he developed this hypothesis based on his observations of information from meteorites. </p><p>A scientist often proposes a <mark class="term" data-term="hypothesis" data-term-def="From the Greek word <em>hypothesis</em> meaning assumption or the basis of an argument, a hypothesis is a proposal intended to explain&hellip;" data-term-url="/en/glossary/view/hypothesis/3727">hypothesis</mark> before <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark> confirms it as a way of predicting the <mark class="term" data-term="outcome" data-term-def="Result." data-term-url="/en/glossary/view/outcome/8247">outcome</mark> of study to help better define the <mark class="term" data-term="parameter" data-term-def="In statistics, a parameter is a numerical value that represents a characteristic of a statistical population. Contrast with statistic." data-term-url="/en/glossary/view/parameter/9481">parameters</mark> of the research. LeClerc's hypothesis allowed him to use known <mark class="term" data-term="parameter" data-term-url="/en/glossary/view/parameter" data-term-def="In statistics, a parameter is a numerical value that represents a characteristic of a statistical population. Contrast with statistic.">parameters</mark> (the cooling rate of iron) to do additional work. A key component of a formal scientific hypothesis is that it is testable and falsifiable. For example, when Richard Lenski first isolated his 12 <mark class="term" data-term="strain" data-term-def="A group of closely related organisms; a distinct variety, as in a strain of bacteria." data-term-url="/en/glossary/view/strain/8288">strains</mark> of <mark class="term" data-term="bacteria" data-term-def="(plural of bacterium) A large group of one-celled organisms that are found almost everywhere." data-term-url="/en/glossary/view/bacteria/8679">bacteria</mark>, he likely hypothesized that random <mark class="term" data-term="mutation" data-term-def="A change in gene sequences of cell DNA." data-term-url="/en/glossary/view/mutation/8757">mutations</mark> would cause differences to appear within a period of time in the different strains of bacteria. But when a hypothesis is generated in science, a scientist will also make an <em>alternative hypothesis</em>, an explanation that explains a study if the <mark class="term" data-term="data" data-term-def="(plural form of <b>datum</b>) A collection of pieces of information, generally taking the form of numbers, text, bits, or facts, that&hellip;" data-term-url="/en/glossary/view/data/3729">data</mark> do not support the original hypothesis. If the different strains of bacteria in Lenski's work did not diverge over the indicated period of time, perhaps the rate of mutation was slower than first thought.</p><p>So you might ask, if <mark class="term" data-term="theory" data-term-url="/en/glossary/view/theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;">theories</mark> are so well supported, do they eventually become laws? The answer is no – not because they aren't well-supported, but because theories and <mark class="term" data-term="law" data-term-def="In science, a principle that describes a phenomenon, often mathematically." data-term-url="/en/glossary/view/law/8686">laws</mark> are two very different things. Laws <em>describe</em> phenomena, often mathematically. Theories, however, <em>explain</em> phenomena. For example, in 1687 <mark class="term" data-term="Isaac Newton" data-term-def="English alchemist, physicist, astronomer and mathematician born in Woolsthorpe-by-Colsterworth, Lincolnshire (1643-1727). In 1672, Newton offered an experimental proof that light is&hellip;" data-term-url="/en/glossary/view/Isaac+Newton/3725">Isaac Newton</mark> proposed a <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">Theory</mark> of Gravitation, describing <mark class="term" data-term="gravity" data-term-def="The natural force that attracts a body toward the center of the Earth, or toward another physical body having mass." data-term-url="/en/glossary/view/gravity/11223">gravity</mark> as a <mark class="term" data-term="force" data-term-def="An influence (a "push or pull") that changes the motion of a moving object (e.g., slows it down, speeds it up,&hellip;" data-term-url="/en/glossary/view/force/883">force</mark> of attraction between two objects. As part of this theory, <mark class="term" data-term="Isaac Newton" data-term-url="/en/glossary/view/Isaac+Newton" data-term-def="English alchemist, physicist, astronomer and mathematician born in Woolsthorpe-by-Colsterworth, Lincolnshire (1643-1727). In 1672, Newton offered an experimental proof that light is&hellip;">Newton</mark> developed a Law of Universal Gravitation that explains how this force operates. This law states that the force of gravity between two objects is inversely proportional to the square of the distance between those objects. <mark class="term" data-term="newton" data-term-def="A metric (or SI) unit measuring force and named for English physicist Isaac Newton. One newton (N) represents the force needed&hellip;" data-term-url="/en/glossary/view/newton/5596">Newton</mark>'s Law does not explain why this is true, but it describes how gravity functions (see our <a href="/library/module_viewer.php?mid=118">Gravity: Newtonian Relationships</a> module for more detail). In 1916, <mark class="term" data-term="Albert Einstein" data-term-def="Theoretical physicist, born in Württemberg, Germany (1879–1955), who became an American citizen in 1940. While working as a patent clerk in&hellip;" data-term-url="/en/glossary/view/Einstein%2C+Albert/4458">Albert Einstein</mark> developed his theory of general <mark class="term" data-term="relativity" data-term-def="In science, relativity usually refers to the general theory of relativity, formulated by Albert Einstein in 1915. Einstein's general theory of&hellip;" data-term-url="/en/glossary/view/relativity/5287">relativity</mark> to explain the mechanism by which gravity has its effect. Einstein's work challenges Newton's theory, and has been found after extensive testing and <mark class="term" data-term="research" data-term-def="A study or an investigation." data-term-url="/en/glossary/view/research/8257">research</mark> to more accurately describe the phenomenon of gravity. While Einstein's work has replaced Newton's as the dominant explanation of gravity in modern science, Newton's Law of Universal Gravitation is still used as it reasonably (and more simply) describes the force of gravity under many conditions. Similarly, the Law of Faunal Succession developed by William Smith does not explain <em>why</em> <mark class="term" data-term="organism" data-term-def="Any connected living system, such as an animal, plant, fungus, or bacterium. Organisms may be composed of a single cell or&hellip;" data-term-url="/en/glossary/view/organism/2171">organisms</mark> follow each other in distinct, predictable ways in the rock layers, but it accurately describes the phenomenon.</p></section> <section id="toc_5"> <h2>Theories, <mark class="term" data-term="hypothesis" data-term-url="/en/glossary/view/hypothesis" data-term-def="From the Greek word <em>hypothesis</em> meaning assumption or the basis of an argument, a hypothesis is a proposal intended to explain&hellip;">hypotheses</mark>, and laws drive scientific progress</h2><p>Theories, <mark class="term" data-term="hypothesis" data-term-url="/en/glossary/view/hypothesis" data-term-def="From the Greek word <em>hypothesis</em> meaning assumption or the basis of an argument, a hypothesis is a proposal intended to explain&hellip;">hypotheses</mark>, and <mark class="term" data-term="law" data-term-def="In science, a principle that describes a phenomenon, often mathematically." data-term-url="/en/glossary/view/law/8686">laws</mark> are not simply important components of science, they drive scientific progress. For example, evolutionary biology now stands as a distinct field of science that focuses on the origins and <mark class="term" data-term="descent" data-term-def="Ancestry or heritage." data-term-url="/en/glossary/view/descent/8285">descent</mark> of <mark class="term" data-term="species" data-term-def="1. In biological classifications, it is the lowest and most basic unit of the Linnaean taxonomic hierarchy (although it is also&hellip;" data-term-url="/en/glossary/view/species/893">species</mark>. Geologists now rely on <mark class="term" data-term="plate tectonics" data-term-def="The study of the processes by which the earth's crust has attained its present structure." data-term-url="/en/glossary/view/plate+tectonics/11229">plate tectonics</mark> as a conceptual <mark class="term" data-term="model" data-term-def="A representation, pattern, or mathematical description that can help scientists replicate a system." data-term-url="/en/glossary/view/model/8236">model</mark> and guiding <mark class="term" data-term="theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;" data-term-url="/en/glossary/view/theory/4854">theory</mark> when they are studying processes at work in Earth's <mark class="term" data-term="crust" data-term-def="The uppermost 5-70 km of the Earth. There are two types of crust: continental and oceanic. Continental crust ranges from 10-70&hellip;" data-term-url="/en/glossary/view/crust/880">crust</mark>. And physicists refer to atomic theory when they are predicting the existence of subatomic <mark class="term" data-term="particle" data-term-def="A tiny piece of matter." data-term-url="/en/glossary/view/particle/8259">particles</mark> yet to be discovered. This does not mean that science is "finished," or that all of the important <mark class="term" data-term="theory" data-term-url="/en/glossary/view/theory" data-term-def="A scientific theory is an explanation inferred from multiple lines of evidence for some broad aspect of the natural world and&hellip;">theories</mark> have been discovered already. Like <mark class="term" data-term="evolution" data-term-def="Change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift." data-term-url="/en/glossary/view/evolution/5284">evolution</mark>, progress in science happens both gradually and in short, dramatic bursts. Both types of progress are critical for creating a robust knowledge base with <mark class="term" data-term="data" data-term-def="(plural form of <b>datum</b>) A collection of pieces of information, generally taking the form of numbers, text, bits, or facts, that&hellip;" data-term-url="/en/glossary/view/data/3729">data</mark> as the foundation and scientific theories giving structure to that knowledge.</p> </div> </section> <hr class="border-color-dark" /> <footer class="module__footer"> <p class="citation"> <em> Anthony Carpi, Ph.D., Anne E. Egger, Ph.D. “Theories, Hypotheses, and Laws” Visionlearning Vol. POS-2 (9), 2009. </em> </p>  <div class="title-list" id="refs" name="refs"> <p class="h6 title-list__title"> References </p> <ul class="title-list__list"> <li>Cook, H., & Bestman, H. D. (2000). A persistent view: Lamarckian thought in early evolutionary theories and in modern biology. <i>Perspectives on Science and Christian Faith, 52</i> 86-97.</li> <li>Dobzhansky, T. G. (1982). <i>Genetics and the origin of species.</i> Columbia University Press.</li> <li>Gould, S. J. (2002). <i>The structure of evolutionary theory.</i> Belknap Press.</li> <li>Horner, W. E. (1843). Remarks on the dental system of the mastodon, with an account of some lower jaws in Mr. Koch's collection, St. Louis, Missouri, where there is a solitary tusk on the right side. <i>Transactions of the American Philosophical Society, 8,</i> 53-59.</li> <li>Johnson, S. (2008). <i>The invention of air: A story of science, faith, revolution, and the birth of America.</i> New York: Riverhead Books.</li> <li>Papadopoulos, D., Schneider, D., Meier-Eiss, J., Arber, W., Lenski, R. E., & Blot, M. (1999). Genomic evolution during a 10,000-generation experiment with bacteria. <i>National Academy of Sciences, 96,</i> 3807-3812.</li> </ul> </div> </footer> </div>   </div>  <div class="order-1 order-2--lg module__tools"> <div class="narrow margin-x-auto position-sticky-top font-size-md"> <div class="padding-2 border-radius box-shadow-1--lg"> <div class="tabs" role="tablist"> <nav> <button class="button button--icon-label" id="tab-button-in-this-module" aria-label="Table of Contents" aria-controls="tab-panel-module__tools" aria-selected="true" role="tab"> <span class="icon icon-list" aria-hidden="true"></span> <span class="button__text">Contents</span> </button> <button class="button button--icon-label" id="tab-button-toggle-terms" aria-controls="tab-panel-toggle-terms" aria-selected="false" role="tab"> <span class="icon icon-glossary-highlight"></span> <span class="button__text">Glossary Terms</span> </button> </nav> <hr class="divider" /> <div class="tabs__panel shown" id="tab-panel-module__tools" aria-labelledby="tab-button-module__tools" role="tabpanel"> <p class="font-weight-bold margin-bottom-1"> Table of Contents </p> <div class="table-of-contents" id="module-toc"> <ul> <li><a href="/en/library/process-of-science/49/theories-hypotheses-and-laws/177#toc_1">Scientific theories</a> </li> <li><a href="/en/library/process-of-science/49/theories-hypotheses-and-laws/177#toc_2">The development of a scientific theory: Evolution and natural selection</a> </li> <li> <ul> <li><a href="/en/library/process-of-science/49/theories-hypotheses-and-laws/177#toc2_1">The Fixity Notion: Linnaeus</a> </li> </ul> </li> <li> <ul> <li><a href="/en/library/process-of-science/49/theories-hypotheses-and-laws/177#toc2_2">The age of Earth: Leclerc and Hutton</a> </li> </ul> </li> <li> <ul> <li><a href="/en/library/process-of-science/49/theories-hypotheses-and-laws/177#toc2_3">Fossil studies lead to the development of a theory of evolution: Cuvier</a> </li> </ul> </li> <li> <ul> <li><a href="/en/library/process-of-science/49/theories-hypotheses-and-laws/177#toc2_4">Studies of invertebrates support a theory of change in species: Lamarck</a> </li> </ul> </li> <li> <ul> <li><a href="/en/library/process-of-science/49/theories-hypotheses-and-laws/177#toc2_5">Rock layers as evidence for evolution: Smith</a> </li> </ul> </li> <li> <ul> <li><a href="/en/library/process-of-science/49/theories-hypotheses-and-laws/177#toc2_6">The theory of evolution by natural selection: Darwin and Wallace</a> </li> </ul> </li> <li><a href="/en/library/process-of-science/49/theories-hypotheses-and-laws/177#toc_3">Expanding, testing, and refining scientific theories</a> </li> <li> <ul> <li><a href="/en/library/process-of-science/49/theories-hypotheses-and-laws/177#toc2_7">Genetics and evolution: Mendel and Dobzhansky</a> </li> </ul> </li> <li> <ul> <li><a href="/en/library/process-of-science/49/theories-hypotheses-and-laws/177#toc2_8">Evolution under a microscope: Lenski</a> </li> </ul> </li> <li> <ul> <li><a href="/en/library/process-of-science/49/theories-hypotheses-and-laws/177#toc2_9">Punctuated equilibrium: Gould and Eldredge</a> </li> </ul> </li> <li><a href="/en/library/process-of-science/49/theories-hypotheses-and-laws/177#toc_4">Hypotheses and laws: Other scientific concepts</a> </li> <li><a href="/en/library/process-of-science/49/theories-hypotheses-and-laws/177#toc_5">Theories, hypotheses, and laws drive scientific progress</a> </li> </ul> </div> </div>   <div class="tabs__panel" id="tab-panel-toggle-terms" aria-labelledby="tab-button-toggle-terms" role="tabpanel"> <div class="reading-toggle"> <div class="reading-toggle__switch"> <div class="form-entry__option__switch"> <label> <input type="checkbox" name="termsToggleSwitch" id="terms-toggle-switch" /> <span class="switch__slider"></span> <span class="option__label text-decoration-none font-size-md"> Highlight Glossary Terms </span> </label> </div> </div> <div class="reading-toggle__help"> <p> <em> Activate glossary term highlighting to easily identify key terms within the module. Once highlighted, you can click on these terms to view their definitions. </em> </p> </div> </div> </div> <div class="tabs__panel" id="tab-panel-toggle-ngss" aria-labelledby="tab-button-toggle-ngss" role="tabpanel"> <div class="reading-toggle"> <div class="reading-toggle__switch"> <div class="form-entry__option__switch"> <label> <input type="checkbox" name="ngssToggleSwitch" id="ngss-toggle-switch" /> <span class="switch__slider"></span> <span class="option__label text-decoration-none font-size-md"> Show NGSS Annotations </span> </label> </div> </div> <div class="reading-toggle__help"> <p> <em> Activate NGSS annotations to easily identify NGSS standards within the module. 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Theories, Hypotheses, and Laws | Process of Science | Visionlearning