CINXE.COM

<!DOCTYPE html><html lang="en-US"><head><title>Just a moment...</title><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=Edge"><meta name="robots" content="noindex,nofollow"><meta name="viewport" content="width=device-width,initial-scale=1"><style>*{box-sizing:border-box;margin:0;padding:0}html{line-height:1.15;-webkit-text-size-adjust:100%;color:#313131;font-family:system-ui,-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Helvetica Neue,Arial,Noto Sans,sans-serif,Apple Color Emoji,Segoe UI Emoji,Segoe UI Symbol,Noto Color Emoji}body{display:flex;flex-direction:column;height:100vh;min-height:100vh}.main-content{margin:8rem auto;max-width:60rem;padding-left:1.5rem}@media (width <= 720px){.main-content{margin-top:4rem}}.h2{font-size:1.5rem;font-weight:500;line-height:2.25rem}@media (width <= 720px){.h2{font-size:1.25rem;line-height:1.5rem}}#challenge-error-text{background-image:url(data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHdpZHRoPSIzMiIgaGVpZ2h0PSIzMiIgZmlsbD0ibm9uZSI+PHBhdGggZmlsbD0iI0IyMEYwMyIgZD0iTTE2IDNhMTMgMTMgMCAxIDAgMTMgMTNBMTMuMDE1IDEzLjAxNSAwIDAgMCAxNiAzbTAgMjRhMTEgMTEgMCAxIDEgMTEtMTEgMTEuMDEgMTEuMDEgMCAwIDEtMTEgMTEiLz48cGF0aCBmaWxsPSIjQjIwRjAzIiBkPSJNMTcuMDM4IDE4LjYxNUgxNC44N0wxNC41NjMgOS41aDIuNzgzem0tMS4wODQgMS40MjdxLjY2IDAgMS4wNTcuMzg4LjQwNy4zODkuNDA3Ljk5NCAwIC41OTYtLjQwNy45ODQtLjM5Ny4zOS0xLjA1Ny4zODktLjY1IDAtMS4wNTYtLjM4OS0uMzk4LS4zODktLjM5OC0uOTg0IDAtLjU5Ny4zOTgtLjk4NS40MDYtLjM5NyAxLjA1Ni0uMzk3Ii8+PC9zdmc+);background-repeat:no-repeat;background-size:contain;padding-left:34px}@media (prefers-color-scheme:dark){body{background-color:#222;color:#d9d9d9}}</style><meta http-equiv="refresh" content="390"></head><body class="no-js"><div class="main-wrapper" role="main"><div class="main-content"><noscript><div class="h2"><span id="challenge-error-text">Enable JavaScript and cookies to continue</span></div></noscript></div></div><script>(function(){window._cf_chl_opt={cvId: '3',cZone: "www.sciencemag.org",cType: 'managed',cRay: '91dbade4db8687a0',cH: 'Butv4gH08UB3JUvoJFnQattMwMOIerlP46wwBLn6wr8-1741534915-1.2.1.1-VyF5X90mELKPoAYlC7IiRyRQ6oFAY83VGo5I7h6F4N5POKOC1CIUE66lZ8giaj41',cUPMDTk: "\/content\/316\/5831\/1585?__cf_chl_tk=MjAcgjWs.L1qVJmplFN8bGCrVrn0JeDo8tLcDuK9TRY-1741534915-1.0.1.1-WxgNC87c4JGIZ4sfVknNAFQnT2zSrZ6f7esicT._hAQ",cFPWv: 'g',cITimeS: '1741534915',cTTimeMs: '1000',cMTimeMs: '390000',cTplC: 0,cTplV: 5,cTplB: 'cf',cK: "",fa: "\/content\/316\/5831\/1585?__cf_chl_f_tk=MjAcgjWs.L1qVJmplFN8bGCrVrn0JeDo8tLcDuK9TRY-1741534915-1.0.1.1-WxgNC87c4JGIZ4sfVknNAFQnT2zSrZ6f7esicT._hAQ",md: ".wYujWYRBDr44DcNg0xm5IGo41Z.luW59iJHZDT96Jc-1741534915-1.2.1.1-ZzCep5uBxcoXVLiESGBMn9es.RCRS0_NXryV3skv4LYyQovyxYaQkO9jkUFs3GLUicnrURRxN8LZV7XGdmraS_NA4lgpYkJNalDIo_rXC22xiFf2dLXNBDXYuebW2JJJtzm8xbIU.ENo2WDVGRuHu5upj_iPG8pJ6sEh.0xDDFZN8ZuaDn3S0kkCkqmaqD772bSo5QNzijs.PGTaq94VZ8tY2yCD8hPiuXczjF3iWwKePJ14bXmlDrHXlj3JZsZDAfOHlY_VKOam0SrUSNCwnKFnZmypPynpkhalyOCEm7OP6Xjm_Cb7_ZfXTJUeSEeGR46KWRqjd_40q3P9rqQQhzaiqPKdVygsqHu1XZBOMG.Q_bYt5DggX.zBB9rdp4gUXv61Im6MTyUw3xg0sQCWjNwmjmzOwVpeYHCuzjOkNsbmu8rV7bVqsPCqy78EUqKRs05fX19P8yZBKP8cWDnrpUsmNVJNtLlhRIpADFiZcKN5oWalHEZjpAyc4X.QnXc_UxOE0zt._6mlm5daFv9ZVV2Ah..ti0p.QdBVrZZOi.rNqqUVo2yP0e4IftvngLntWfwayyJNK75Qs39flfNXzsCBomiPs1ehYHF1J7P.qc0QanWNz5hVUKHLOoZg7nS_01ovgwnMd2bqVzxtMqvEgEn9oImYLHJBw6HvyqZYHITl5kTDtyJEvD1vFYmcR_Vtmz2XKfhFIhKxGstY9eAIszsymkQ128rks9KjiXlJapZBh0tI1F51yCsO9KNHg.Cwt.ub8q3NwumHxBjRX2U8YvImpva.FL3x7wzCZttykgWra82IigKOUmC8uFBm9.X93l55K4_Q_BZkbJ9A6jygDGxufl246kbHc2hFfr_wTAaMa0pNCWG8pvXB2fWmDSv7gTgnLJZdtbQKnGDMA7nstv52xUK2odAeEMzL02F9EeuAT9jA6DPqul0Mtm4OnzUAQXg.2q1QhaQceZHQ._00wePKVkiI1n.SZAjnTPolZK0NkcX0W4QeLj5I7jzHk3nHUm8B6teYA.q1hiFkYjOPDnrrn7d1jWhudhtb4SeNUDPgj.e97tSUo9YGtT1JK5tn3CoU.lkp0Huf0r56M6k15E7gJjwhSgDdbIL_jEBBZMSWfQ6cIxkW1eHcoky4Rp3PeVMR2h6t1vuN0L5DZfc9b9dljR57ybnflY.8vwF1VbbiHIGSmF14h3Q1nSkirvGKNIXKhp0PHRAr9BxJ0kyEFae3I1l_dbsUZdgJMSKo4c_1rNyiKUda8Vors4DIzFti",mdrd: ".nrqAg3Op0DbjbKiD6S5Jp5s88IB7vuDZDfNKOv1ydQ-1741534915-1.2.1.1-.v9GLcxrR5rHnKeD5W31JSjWj.hSwQfVBwYVTpnyuxmBqXs216A8QbEYMa8398ni.Otl3VFaHsE8rkUkwwk1lkKgaKoaftFXWGb4Y2oNwj7CBfoo9qvHCRjn64AzRfyf7VwNBgxAgpQp4Oyt4RQNg0zEznNj8XS2A__eOcgKNLLaVjmCuh4D2zYjGhVwoivohF86CoJ.M8lgCu.S4uxbKXoEEN4djtP_N62C2OSpNlGr5sT7zXOJ9IcDBq9CikYI85l_32Ax16TVut1Cp6bpkfIGWPttfozX5OQMDGxK5uNhozy8mK7gtXC2S58OTICHvZ.96uXBHgjB1foury_NKsQ_1X3SPcjQ09PU7INR4e0pkC8_yaeShEmahTr4IAdfJHPAq.Mns6V6typSGO3E.ajgpU4NmLi0JJ8f2Lz9v3BAbHCdJngqAeu3BRMLGGktXcTAT2pMUJOctbZFba26vp_lEBrYwx0wDtwQble.MYkTcdplyetdwLErE74m6IH0rsul8NjXP3.sepoLg05pTbWNGchpRCfi1KU5MB4el3SporlFXTcaE695ZzS25qqHTU1RQyVIuXOo2y4NH0SXd5Lmb1ryV3dReumfVnvfp4BV1dgksxbuccewxJ6lRbCjB5_ZWRRkFcxrRz0iq1zzJa0GyHhRqm7dvwznb5llQwl3ERgkoNgNZUA0dwGYh5xw"};var cpo = document.createElement('script');cpo.src = '/cdn-cgi/challenge-platform/h/g/orchestrate/chl_page/v1?ray=91dbade4db8687a0';window._cf_chl_opt.cOgUHash = location.hash === '' && location.href.indexOf('#') !== -1 ? '#' : location.hash;window._cf_chl_opt.cOgUQuery = location.search === '' && location.href.slice(0, location.href.length - window._cf_chl_opt.cOgUHash.length).indexOf('?') !== -1 ? '?' : location.search;if (window.history && window.history.replaceState) {var ogU = location.pathname + window._cf_chl_opt.cOgUQuery + window._cf_chl_opt.cOgUHash;history.replaceState(null, null, "\/content\/316\/5831\/1585?__cf_chl_rt_tk=MjAcgjWs.L1qVJmplFN8bGCrVrn0JeDo8tLcDuK9TRY-1741534915-1.0.1.1-WxgNC87c4JGIZ4sfVknNAFQnT2zSrZ6f7esicT._hAQ" + window._cf_chl_opt.cOgUHash);cpo.onload = function() {history.replaceState(null, null, ogU);}}document.getElementsByTagName('head')[0].appendChild(cpo);}());</script></body></html>