The National Academies

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head><script type="text/javascript" src="/_static/js/bundle-playback.js?v=HxkREWBo" charset="utf-8"></script> <script type="text/javascript" src="/_static/js/wombat.js?v=txqj7nKC" charset="utf-8"></script> <script>window.RufflePlayer=window.RufflePlayer||{};window.RufflePlayer.config={"autoplay":"on","unmuteOverlay":"hidden"};</script> <script type="text/javascript" src="/_static/js/ruffle/ruffle.js"></script> <script type="text/javascript"> __wm.init("https://web.archive.org/web"); __wm.wombat("http://www.national-academies.org:80/legal/","20080702130634","https://web.archive.org/","web","/_static/", "1215003994"); </script> <link rel="stylesheet" type="text/css" href="/_static/css/banner-styles.css?v=S1zqJCYt" /> <link rel="stylesheet" type="text/css" href="/_static/css/iconochive.css?v=3PDvdIFv" />  <meta http-equiv="pics-label" content="(pics-1.1 "http://www.icra.org/ratingsv02.html" comment "ICRAonline v2.0" l gen true for "http://www.national-academies.org" r (nz 1 vz 1 lz 1 oz 1 cz 1) "http://www.rsac.org/ratingsv01.html" l gen true for "http://www.national-academies.org" r (n 0 s 0 v 0 l 0))"> <meta http-equiv="content-language" content="en"> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <meta name="Description" content="The nation turns to the National Academies -- National Academy of Sciences, National Academy of Engineering, Institute of Medicine, and National Research Council -- for independent, objective advice on issues that affect people's lives worldwide."> <meta name="Keywords" content="National Academy of Sciences, National Academy of Engineering, Institute of Medicine, National Research Council, National Academies, NAS, NAE, IOM, NRC"> <meta name="Identifier-URL" content="www.nationalacademies.org"> <link href="https://web.archive.org/web/20080702130634cs_/http://www.nationalacademies.org/nav/na_styles6.css" rel="stylesheet" type="text/css"> <meta name="generator" content="Fog Creek CityDesk 2.0.25"/> <meta name="citydesk" content="4FA27437/90"/> <title>The National Academies</title> <script language="JavaScript">  </script> </head> <body> <table width="100%" border="0" cellspacing="0" cellpadding="0" bgcolor="white"> <tr> <td valign="top">  <table cellspacing="0" cellpadding="0" border="0" width="100%"> <tbody> <tr> <td bgcolor="#000066" align="left" valign="middle" height="56" width="25%"><a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/"><img src="https://web.archive.org/web/20080702130634im_/http://www.nationalacademies.org/includes/tnalogo.jpg" alt="The National Academies: Advisers to the Nation on Science, Engineering, and Medicine" title="The National Academies: Advisers to the Nation on Science, Engineering, and Medicine" border="0" align="bottom" width="350" height="56/"></a> </td><td rowspan="2" width="10%" height="56" bgcolor="#000066">  <a href="#TN" class="invisible" style="font: 3pt verdana">Jump to Top News</a><a href="#SITH" class="invisible" style="font: 3pt verdana">Jump to Science in the Headlines</a> </td> <td align="right" bgcolor="#000066" style="padding: 5px;" height="56" width="65%"> <table cellpadding="0" cellspacing="0" bgcolor="#000066" border="0"> <tbody> <tr><td valign="top" height="48" width="205" style="font-size: 12px"><div align="center">  <form method="get" action="https://web.archive.org/web/20080702130634/http://search.nationalacademies.org/search"> <table> <tr> <td> <input type="text" name="q" size="17" maxlength="255" value=""/> <input type="image" name="sa" value="Search" src="https://web.archive.org/web/20080702130634im_/http://www.nationalacademies.org/nav/images/searchbutton2.jpg" alt="Search" align="absmiddle"> <input type="hidden" name="site" value="main_collection"/> <input type="hidden" name="client" value="nax_frontend"/> <input type="hidden" name="proxystylesheet" value="nax_frontend"/> <input type="hidden" name="output" value="xml_no_dtd"/> </td> </tr> </table> </form>  <p><a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/mail.html" class="subscribe">Subscribe to our FREE e-newsletter!</a></p> </td> </tr> </tbody> </table> </td> </tr> </tbody> </table> </td> </tr>   <tr> <td valign="top" height="20"> <table width="100%" border="0" cellspacing="1" cellpadding="0" bgcolor="white" align="left" style="padding-bottom: 2px;"> <tbody> <tr> <td bgcolor="#666699" onmouseover="this.style.backgroundColor='#000066';" onmouseout="this.style.background='#666699';" valign="middle" align="center" nowrap width="28%" height="20"><a href="https://web.archive.org/web/20080702130634/http://www.nasonline.org/" class="inst" style="font: 7pt verdana; color: white; text-decoration: none;">NATIONAL ACADEMY OF SCIENCES</a> </td> <td bgcolor="#666699" onmouseover="this.style.backgroundColor='#000066';" onmouseout="this.style.background='#666699';" valign="middle" align="center" nowrap width="28%"><a href="https://web.archive.org/web/20080702130634/http://www.nae.edu/" class="inst" style="font: 7pt verdana; color: white; text-decoration: none;">NATIONAL ACADEMY OF ENGINEERING</a> </td> <td bgcolor="#666699" onmouseover="this.style.backgroundColor='#000066';" onmouseout="this.style.background='#666699';" valign="middle" align="center" nowrap width="19%"><a href="https://web.archive.org/web/20080702130634/http://www.iom.edu/" class="inst" style="font: 7pt verdana; color: white; text-decoration: none;">INSTITUTE OF MEDICINE</a> </td> <td bgcolor="#666699" onmouseover="this.style.backgroundColor='#000066';" onmouseout="this.style.background='#666699';" valign="middle" align="center" nowrap width="25%"><a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/nrc/" class="inst" style="font: 7pt verdana; color: white; text-decoration: none;">NATIONAL RESEARCH COUNCIL</a> </td> </tr> </tbody> </table> </td> </tr>   <tr> <td style="padding-left: 5px;" valign="middle" height="20"> <table width="100%" border="0" cellspacing="0" cellpadding="0" align="left"> <tbody> <tr> <td valign="top" width="1" height="20" style="font: 8pt verdana, arial, sans-serif; color: #999999; padding-top: 2px; padding-bottom: 2px;" nowrap> </td> <td valign="top" height="20" width="500" style=" padding-top: 2px; padding-bottom: 2px; color: #666666;" nowrap> </td> <td height="20" valign="top" style="padding-bottom: 0px; padding-right: 10px; padding-top: 4px;" align="right" nowrap> <script type="text/javascript" language="JavaScript1.2"> </script> </td> <td valign="top" height="20" width="160" nowrap style="padding-bottom: 3px; padding-left: 3px;" align="right"><a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/status/" class="leftlink"><img src="https://web.archive.org/web/20080702130634im_/http://www.nationalacademies.org/includes/opstatus2.jpg"></a> </td> </tr> </tbody> </table> </td> </tr>  <tr> <td valign="top">  <table width="100%" align="left" border="0" cellpadding="0" cellspacing="0"> <tr>  <td valign="top" width="150" align="left"> <table width="150" border="0" cellspacing="0" cellpadding="0" style="padding-left: 3px;"> <tbody> <tr> <td valign="bottom" align="left"><img alt="Quick Links" src="https://web.archive.org/web/20080702130634im_/http://www.nationalacademies.org/nav/images/tab_ql.gif" width="150" height="20" align="top" title="Quick Links"/> </td> </tr>  <tr> <td valign="top"> <table width="150" border="0" cellspacing="0" cellpadding="0"> <tbody> <tr> <td class="leftnav" style="border-top: 1px solid silver;" valign="top"><a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/about" class="leftlink">About the National Academies</a> </td> </tr> <tr> <td class="leftnav"><a href="https://web.archive.org/web/20080702130634/http://www8.nationalacademies.org/cp" class="leftlink">Current Projects</a> </td> </tr> <tr> <td class="leftnav"><a href="https://web.archive.org/web/20080702130634/http://www8.nationalacademies.org/onpinews/default.aspx" class="leftlink">News Office</a> </td> </tr> <tr> <td class="leftnav"><a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/publications/" class="leftlink">Publications</a> </td> </tr> <tr> <td class="leftnav"><a href="https://web.archive.org/web/20080702130634/http://www7.nationalacademies.org/ocga/" class="leftlink">For Congress</a> </td> </tr> <tr> <td class="leftnav"><a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/memarea" class="leftlink">Members' Site</a> </td> </tr> <tr> <td class="leftnav"><a href="https://web.archive.org/web/20080702130634/http://www.koshland-science-museum.org/" class="leftlink">Marian Koshland<br>Science Museum</a> </td> </tr> <tr> <td class="leftnav"><a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/giving/" class="leftlink">Giving to the National Academies</a> </td> </tr> <tr> <td class="leftnav"><a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/directories/" class="leftlink">Directories</a> </td> </tr> <tr> <td class="leftnav"><a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/cgi-bin/formfeed.cgi" class="leftlink">Contact Us</a> </td> </tr> <tr> <td class="leftnav"><a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/coi/index.html" class="leftlink">Conflict-of-Interest Policy</a> </td> </tr> <tr> <td class="leftnav"><a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/studycommitteprocess.pdf" class="leftlink">National Academies Study Process</a> </td> </tr> <tr> <td class="leftnav"><a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/sitemap/" class="leftlink">Site Map</a> </td> </tr> </tbody> </table> </td> </tr> <tr> <td height="5" valign="top">  </td> </tr> <tr> <td height="10" valign="top"> <a href="https://web.archive.org/web/20080702130634/http://www.nas.edu/podcast/" class="leftlink"><img src="https://web.archive.org/web/20080702130634im_/http://www.nationalacademies.org/includes/mp3logo_tiny.jpg"></a><a href="https://web.archive.org/web/20080702130634/http://www.nas.edu/podcast/" class="leftlink"> Podcasts</a> </tr></td> <tr> <tr> <td height="10" valign="top"> <a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/about/rss.html" class="leftlink"><img src="https://web.archive.org/web/20080702130634im_/http://www.nationalacademies.org/elements/rss.JPG"></a><a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/about/rss.html" class="leftlink"> News Feeds</a> </td> </tr> <td height="10" valign="top">  </td> </tr> <tr> <td valign="top" align="left"> <table width="150" border="0" cellspacing="0" cellpadding="0" align="left"> <tbody> <tr> <th class="newhead" align="left"> Popular Searches</th> </tr> <tr> <td class="new"> <a href="https://web.archive.org/web/20080702130634/http://nationalacademies.org/evolution" class="leftlink">Evolution</a> </td> </tr> <tr> <td class="new" style="border-bottom: 1px solid silver;"> <a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/stemcells" class="leftlink">Stem Cells</a> </td> </tr> </tbody></table></td> </tr> <tr> <td height="10" valign="top">  </td> </tr> <tr> <td valign="top" align="left">  <table width="150" border="0" cellspacing="0" cellpadding="0" align="left"> <tbody> <tr> <th class="newhead" align="left"> Career Links </th> </tr> <tr> <td class="new"><a href="https://web.archive.org/web/20080702130634/http://www7.nationalacademies.org/careers" class="leftlink">Employment</a> </td> </tr> <tr> <td class="new" style="border-bottom: 1px solid silver;"><a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/opportunities" class="leftlink">Fellowships & Postdoc</a> </td> </tr> <tr> <td class="new" style="border-bottom: 1px solid silver;"><a href="https://web.archive.org/web/20080702130634/http://nationalacademies.org/careerguides.html" class="leftlink">Career Guides</a> </td> </tr> <tr> <td class="new" style="border-bottom: 1px solid silver;"><a href="https://web.archive.org/web/20080702130634/http://www7.nationalacademies.org/retirees/index.html" class="leftlink">For Retirees</a> </td> </tr> </tbody> </table> </td> </tr>  <tr> <td height="10" valign="top">  </td> </tr> <tr> <td valign="top" align="left"> <table width="150" border="0" cellspacing="0" cellpadding="0" align="left"> <tbody> <tr> <th class="newhead" align="left"> Major Divisions </th> </tr> <tr> <td class="new"><a href="https://web.archive.org/web/20080702130634/http://www7.nationalacademies.org/dbasse/" class="leftlink">Division of Behavioral<br>and Social Sciences<br>and Education</a> </td> </tr> <tr> <td class="new" style="border-bottom: 1px solid silver;"><a href="https://web.archive.org/web/20080702130634/http://dels.nas.edu/" class="leftlink">Division on Earth<br>and Life Studies</a> </td> </tr> <tr> <td class="new" style="border-bottom: 1px solid silver;"><a href="https://web.archive.org/web/20080702130634/http://www7.nationalacademies.org/deps/" class="leftlink">Division on Engineering<br>and Physical Sciences</a> </td> </tr> <tr> <td class="new" style="border-bottom: 1px solid silver;"><a href="https://web.archive.org/web/20080702130634/http://www.iom.edu/" class="leftlink">Institute of Medicine</a> </td> </tr> <tr> <td class="new" style="border-bottom: 1px solid silver;"><a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/gateway/pga/" class="leftlink">Policy and Global<br>Affairs Division</a> </td> </tr> <tr> <td class="new" style="border-bottom: 1px solid silver;"><a href="https://web.archive.org/web/20080702130634/http://www.trb.org/" class="leftlink">Transportation<br>Research Board</a> </td> </tr> </tbody> </table> </td> </tr> </tbody></table> </td>   <td valign="top" style="padding-left: 5px; padding-right: 5px;" align="left" width="100%"> <img height="20" alt="Legal Information" src="https://web.archive.org/web/20080702130634im_/http://www.nationalacademies.org/elements/legal_tab.gif" width="182" align="top"/> <table border="0" cellspacing="0" cellpadding="20" width="100%"> <tbody><tr> <td valign="top" width="50%" style="border-top: 1px solid silver; border-bottom: 1px solid silver; border-left: 1px solid silver; border-right: 1px solid silver;">  <ul class="blurb"> <li><a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/legal/policy.html">Digital Millennium Copyright Act Policy & Contact Information</a> </li> <li><a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/legal/security.html">Security Statement</a> </li> <li><a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/legal/privacy.html">Privacy Statement</a> </li> <li><a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/legal/terms.html">Terms of Use</a> </li> </ul> <p class="blurb">Copyright 漏 <script language="JavaScript" type="text/javascript"> //<![CDATA[  //]]> </script> National Academy of Sciences. All rights reserved.</p> <br/> <p class="blurb">Unless otherwise indicated, all materials on these pages are copyrighted by the National Academy of Sciences. All rights reserved. No part of these pages, either text or image may be used for any purpose other than personal use. Therefore, reproduction, modification, storage in a retrieval system or retransmission, in any form or by any means, electronic, mechanical or otherwise, for reasons other than personal use, is strictly prohibited without prior written permission.</p> <br/> <p class="blurb">The identifier "the National Academies" refers collectively to the National Academy of Sciences, National Academy of Engineering, Institute of Medicine and National Research Council.</p> <br/> <p class="blurb">General inquiries should be directed to our Web feedback box, <a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/cgi-bin/formfeed.cgi">accessible from this link</a> or from the footer at the bottom of most pages on our site.</p> <br/> <p class="blurb">Messages posted to some areas of the National Academies Web site are not private. If you post a message, anyone with access to the message area can read it, and your e-mail address becomes available to anyone who browses or uses the message area. Please keep in mind that the National Academies cannot control who sends you e-mail as a result of postings to this service.</p>  </td> </tr> </tbody></table> </td> <tr><td height="10" colspan="3"></td></tr>  <tr> <td valign="absmiddle" align="center" bgcolor="#666699" colspan="3" height="20"> <a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/about/rss.html"><img src="https://web.archive.org/web/20080702130634im_/http://www.nationalacademies.org/elements/xml.gif" alt="RSS News Feed" width="36" height="14" align="absbottom"></a> | <a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/subscribe.html" class="bottomlinks">Subscribe to e-newsletters</a> | <a href="https://web.archive.org/web/20080702130634/http://www.nationalacademies.org/cgi-bin/formfeed.cgi" class="bottomlinks">Feedback</a> | <a href="#top" class="bottomlinks">Back to Top</a> </td> </tr> <tr> <td colspan="3" valign="top" align="center"> <div class="copyright"><a href="https://web.archive.org/web/20080702130634/http://www.national-academies.org/legal/" class="copyright">Copyright © 2008. National Academy of Sciences. All rights reserved. 500 Fifth St. N.W., Washington, D.C. 20001.</a> <br> <a href="https://web.archive.org/web/20080702130634/http://www.national-academies.org/legal/" class="copyright">Terms of Use and Privacy Statement</a> </div> </td> </tr> </tbody></table> </tbody></table> <script type="text/javascript"> var gaJsHost = (("https:" == document.location.protocol) ? "https://web.archive.org/web/20080702130634/https://ssl." : "https://web.archive.org/web/20080702130634/http://www."); document.write(unescape("%3Cscript src='" + gaJsHost + "google-analytics.com/ga.js' type='text/javascript'%3E%3C/script%3E")); </script> <script type="text/javascript"> var firstTracker = _gat._getTracker("UA-3065995-1"); firstTracker._initData(); firstTracker._trackPageview(); var secondTracker = _gat._getTracker("UA-2130316-1"); secondTracker._initData(); secondTracker._trackPageview(); var thirdTracker = _gat._getTracker("UA-3310925-1"); thirdTracker._initData(); thirdTracker._trackPageview(); </script> </body></html>

CINXE.COM

The National Academies