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,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);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.science.org",cType: 'managed',cRay: '8f03f1a859368249',cH: 'KtcKCLKBniUE820dZ.tXVgmA2D6pvLoLyfK3ooBkTsA-1733904057-1.2.1.1-EUCMeRcHdQ2gsWzqZl_P.6mpBe5pBzht_57917ILkxZYLnb5uZc_9iSrO6nWSht4',cUPMDTk: "\/doi\/10.1126\/science.173.3997.585?__cf_chl_tk=Zoo4i0RPWe5_.ZJbKqFGI8ci8GySJsMj3XjlTLfAe40-1733904057-1.0.1.1-_A5GhE6Shve.tNZUPCJYmR2Pn7JIVvyatITX6Zfe2nI",cFPWv: 'g',cITimeS: '1733904057',cTTimeMs: '1000',cMTimeMs: '390000',cTplC: 0,cTplV: 5,cTplB: 'cf',cK: "",fa: "\/doi\/10.1126\/science.173.3997.585?__cf_chl_f_tk=Zoo4i0RPWe5_.ZJbKqFGI8ci8GySJsMj3XjlTLfAe40-1733904057-1.0.1.1-_A5GhE6Shve.tNZUPCJYmR2Pn7JIVvyatITX6Zfe2nI",md: "RfKryYBPmQYhad57kARcIbz7dJXCDJ9NxcTi_pG2PS8-1733904057-1.2.1.1-osgaNRWoK6CpGnsb4WS4rbpqO4hDqEKvWR9.YoXcdaolX89dAqhygl1NJVALqnHBJCWoLnoUhIFlDK2FUd0Un2uylGTF6epAqBt_M9tZgA7Wi49v8t5258h0we44hp8HZl051BTu.xuRdzPR95b7WuywYUaZQwCg2kP8FYe.XZVscEmlgl7oa19DZhsjxTK9O8DKEYMjF.5QK.N1yZzs4hiAH.O5vVjInBZRe5RumhfF7IUcdIe9GDiK1Mx9jDGYWl874Zbzr41cfmwj9sqplegKFeH5BMXAetiDCPq5svAZGyKkj66tDzyyxTu9r70dRh7ii95.sxhGvNW8CKiYpK2GReRZZRd8eRrLKv3k4Uj85yHLzc7_8sy4M9wXiw8soPbIHaKESo9.iRtjjPZGHAnPsQDbk4WxKOtdUbynsjdIVILyyxx4TEAuC0sCiAYB1UTmuw132Kunvo5ReGOXpvSEExVJY3s9WeVk7zMkh3LX2m2von8Jfm1Dc.u9k8ZCvUjqFz1WazLD5wMLOptBlZtDdIvMrCgsbJXAbRLjjaRTNrSlUJkqZX.wicDDAH7nh6UFDAqQx387A45Ek9HAINagJE.F2C2Qeiq_SythBDYLgIP9cu7J.q9N8ZnGSWpuEpJ8rM8ijQoPgDaaXGTUoutLsoB5GAF_hBi1TXMksmJn9yYVWWl4axwNZVHbA0__4R3ewN_gzHH5P1fTXg6HsmjM3QTa6B_HcQ_piIrW_afGT3C9vnjkFvkyAXeBDO2GWdTTejHO7Flp1J.Tx3XKRMPNzWrTHpmuvA4euOZqcFbBY75bWflKg4J1oZiuoCPpCh8hA78C3TLjouqVtQtEzpMIX9.uuKz0YF4rzGnNz58pwyYnnLjBFfwbmM9mgbfsKalmDmLkLqiAH4OcHqiF3gzFzrSDDn5boeZ28TwgRtdgsfOOvo99ABOeb5_7wMaZ1PR4ye2_wRttX8RZc7jmX_Pnu4VBk11TZRAIoKkCybSmLVYzs3.mWnkWkIrNY1ZrpRppJ7Lmf2vvivH6kc3Uovj1E0jA80NC.zFpOayByqrL65f4UKM3ihld5P4Rsi2OFkhGrmX.0Gl_fto4fjnJLz9WUUlR57bGhjCkDuMmt6pJFWZtplvhARfsEWBWiF3uIGtAobPtciNN8o_B4GU4P7DGKZymiRq5h954W_hmn2WiwSZWLbIve5KQLowuYHty7re1F_4GKDfvECkYzJOn9NVpKlI1PFqcou1sDOwj6tk83xL_Qi.HDc_ey3oxxjBf0PqYHVhCltJjVConNQd8OCDfjswpd5bQ5nfkJcePaKbQ7pWC1zppNsEVD15J_Y6BXG9OISovrLyKInjGYWaP0yI.0rOyk9Z2JylSK0xM0X.GZaNY_UCnyFFl.j42cLhnb272cHVyD7JDAzxi9WF_Fm3hkrVEwUL3JZZZiI4sSTByRQ8vTejyn9bgRmPsEhBU345RunxhR7aUAdpyz8e4ca2qTslWolZDoYGYcxEOLZWdcgROlTxF2HgJ2XqIYed1YO8g69Y8UvgARaZMDqxYrOaf8zo.OeXsGEsWEhjQRk7n5QRxka2Q3IUd3E7O3QuDejXW7PNdEwAl73VyLCtfi4zyUktj.Y8IoSF8s5oJx3uNm4KwLZyhiyPu9mWLP8JZ2eXn9XaK8MPZP0OeyrRcjy29QvQVBv_Opr8ipeOpI76akiHodv9VlUZUubFGMOoznCZ997t2QPS0cr.20hh5vWDpBBWmZ6QfikRPyGJ9O5YVF3KXv4NKxZ4TCES1B5Z4UizkPugojqEM_oi2yZ1CeJ4.9ok6yp6aM41S.yVr2yUyDOX5QLW5ong6PnbJuCocT.TbeL_Kdx7Rbreho_a36XE.6Vr5qydlVEbkV6ky4ignnX3NXL5eMtpsOF6aA8ioxHYwrhaOyuDH6jF7Ue9RsWn18IQLMOHzlsyCTXBcxaOSdDxFcs0VASiCSbafGzqTdEnpi5yoA82aMnCpnq0utPL4XVbTumCcB7uGicUX29QEGQS3soNYYWS_eooemjF4TH3xHMLAvHT6S8kS.0_MQskkDyOJlzVe7dBMKE0wTPIBhN2lsrca.pDcIGqhNnnifLPdcMLj2SzEQgNmOq3ONNhLEjQLRWpdu2JB2ctClx8AZ7jrWiOIg_4kk6qfPX545DO3PyPAv6uY0fkwglHHcBiPaJwVk8NzQM8KpUhKvywpmEkDAK9WngqwNhh8Msxg43olfuEEVDDJzbyDPFV8BqLd0Ne9D3ZQAR01Bvrx8FeBYkWjFfvCTw4im_fQbvpcYAlVvQdD6dKMjD5UImdacTZZjxQx9lkpzyPDMsOUBoE8iPYDL4Mr4Wjz6_pfbdouzWvebM2cEtJsl4082mLEsjSpvuP04J6RcxFGtdObh5jxzjPLviAdWD0yn2MdhablWZdaIjkKwvM7vvkb3HS0MynB4YHsHn_NqJfDa0_NjlFE2JcRdpTbftVIzlb63NqNjXPzJFzUs1T8QdWTLY8kzUCUCNCg_EIaKNgG3cBom4hrzATE984_eViUE7WEP1XzfhZbP69iKmX7t.hBFAKDcnQz_vLZtCRrtrcS9N_EvE.ygOWSUDbP9aTQOmNsEBkTSZbHSkPghhSG0TTwq_1fOvbcCatpWMM6c3jkdrUEJQeuL8.1IUVOJ5Flf5xIh6jHiJ06yrLx3anZzFuXH9pmheX1zAhR1XEUG5LX8lj_soMy1BF0sgfx08d.Kia3qpjSV0880lkUvfEkuJzjSjH0nuz8mGJyL_v57amd1C7liCFOkkhHauG8O0hqROziZKOqjwm3LjytoHUzTnMeCCrObcHsCkYuXtlxMGXi_9ndjmaKvDksnviLTEgQgz81HU_rj.obf0Wt.aXmwsWwyA0FyoOgwR54dQO3CgWp19IiPU7T6pMJOxQp7wzokX7VyxlYtzIjlrHVuiPXNAOiUe5SjaCR2msBO44D9T9_cxwVGOyimKktmsJi4zXh3TMEVwgr",mdrd: "k8BffUFV4Cci_6ia3lCRjEdLSOkMnNUg5LH.W5yLgbk-1733904057-1.2.1.1-kij4TtqR89D9Sn5vetuOxHqfDQwIyXKutFdEijYRyvcyGWvEIjBIgdxYdluSfRvUiVYt6A5JvaMwzZXykT.fxu_Vjyq6asXgFNJmlXHkYqz8jR8i_5N8BtCWJAVFiA0JvXPxy6I5j9dvNGqsJyAidkGxp5XfGk.7R9IzxXaiWNtw7KW.6D4MwvLq3I2_5bFmUl8t_bPfxIL59mdjee.AIBoKM3Alc3Rvgp5VDvKM2o.YZAsRNLljaK080uzxcN0m2Uge0PAkypuJ3QI5Wfk00iP4tIEaKbsyz_TxLlYDj2ir1FVOZbsf5D9tIfk_9KNdXqztkxgX27WHyt.2GqRtlj8L7D6DZ9sTKf9x5xKJywl8v7wwZVXf7RFMpcCbp2Picb5NxQyCsrW8T6eKl2ICjPMUlXEJAorTDQ2k7QrAvI._AieXsD5UfNlBZ.9ktwQZPiDu.SZQje1Cnq5oKIQD_8MR0B0wkfVsrRsvzwXMqLeU816DEAKz74OPhzZjMKinivliP6u1.5XItH37R4827Sp6lJbSlZOyFrvLZNXXDE4iHV0qDSg88.OQXttqzFrYyO6RNoz52ELkd7WYhHFJyBdd1voLqjx8XAtamAcJX5Zwho1F0J3zCXfbtVdknQUHx_rE_Uo4oOxhMviUOP5mmgxvdUGRx9euqG3fLNhy4J50MeAjVvYFMT2vDLeAnMrq0tMuTCn7HCsmoN2xvjJM7fFqE2A6gCUSQt0ft_f6SR7C.OYn.XDdst2vPGndS1xZkohSJO0BPFbikhWXtxfxnayfdF0Dzm6FuVcURgWiCNlrg6efHrcowLAapu8ye6hPe9oOSIyyfQVQj93gtlEJTpMvH.QPda2js8S4A0Q3g1mE6eGPtwD1ndEJzDL6rLPPrU38vqgmmRpLoi1Lr884fsYnzMuMlrY73mlrYiB7mpnrs51pyXYG5cUmpG1LN352X36dnbyOYAVQhSHA9SigTVHLbdOPGWYrSeCy4FAiYVEQcs1fnM29GphnVf.v7CNf6JthKaSWNS.9IjgJaMB8LYFHAm.IxlQbmf3X62L44SoeYJMhV3nUsV9IUNj_.7mkaFfltEuIYk3wBNNFxZJf6hIawIsK11yN1wFMKlFMh5PiEtQFCG.kbjjEk9WLG1Xuldo6OSWZnhIsYUaLPtr0yZwvwSAmSXU9Fc4MgHhyr53hkpuI.KD.LwdfHSWtIevVLnKOZBz_Ftie1CNK1QsRLecdvX53UeEg1KM3n26F76l2_qFnKnDGBptaMbFEAmnhbbubpmIZ4sa3kWHrr1Irx3FToqtTt3R_eOpTzgWmrZ4Lj6rOoI3or5pvN7iZKeYuTJ6AcmBDcN1u7mlKGNn.lV5m7TFFTEpn57w1CwePfJOQh1j1cV2pgWfb6ZdiMZKvUxX9cnr..g19XvChNMkqqd5iBJcIhY.kuVUU_ldOfQ8st02lQel54yhRCRceMgxqQ4x5eYsO5j5foT__iE6M6qMkjR9pDVyZuCcxH.x6xoVuMbE4YUO.b4QB0LES.IZ5fDnWw9FyTP7Apl1v2anBfLutrutINOrc7g7Oksb0yEwJLYx9ZwKXoDqh_yNq_jikFUA_iW8siN5EB5wq.0zUY6dqz8eO8tdou2pDSPdEEpv2vLQ5199tlkUIayCTVYsJb7HvmFZfEz3D0rJ6LS2owzthdHt.QwWc5DiPGVsTWE2avIVOrosRf.azLn3NTm4i7nDWrc702fFbQuapcxa0SZdT4xY5nmU_sA6BL1ThzHZZ7L2q5Wis8tO.c6E2fBPWtpaLhoOLhp4TaKF3hVS57OBlmBf1BbBV4YaL3x_60_9.WCRhRDsFSND4wfBn6SON3jl2UFk7bNsrvj6AV1wkB7k64L.J3M1y6dYF4Kw_cMkCws94_uxlTZ5KEs0JuiZduucVXWSIkCvPsCFZED71otfY.EjNdiJupyt3EBD0fOI"};var cpo = document.createElement('script');cpo.src = '/cdn-cgi/challenge-platform/h/g/orchestrate/chl_page/v1?ray=8f03f1a859368249';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, "\/doi\/10.1126\/science.173.3997.585?__cf_chl_rt_tk=Zoo4i0RPWe5_.ZJbKqFGI8ci8GySJsMj3XjlTLfAe40-1733904057-1.0.1.1-_A5GhE6Shve.tNZUPCJYmR2Pn7JIVvyatITX6Zfe2nI" + window._cf_chl_opt.cOgUHash);cpo.onload = function() {history.replaceState(null, null, ogU);}}document.getElementsByTagName('head')[0].appendChild(cpo);}());</script></body></html>