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: '8e92504b5eb3ce59',cH: 'b23mHW7yBT3cVBzqKmDfM_NW.wGr6.wr1YIUD67ROk8-1732712557-1.2.1.1-XjjCUcbiUXdPF0D84iYhhkMQVKHF8bu3tarXRnptteq5cE2OMA.tdeKyGKqtJ1KQ',cUPMDTk: "\/doi\/10.1126\/science.149.3683.510?__cf_chl_tk=a1piCQBQsovS5TF8GIe_6aXhDykwqetHSnns0L1Dwmw-1732712557-1.0.1.1-aQNg.hlbOOgIdWdwNdMXso2tvAt5PTArCvungYSOfpQ",cFPWv: 'b',cITimeS: '1732712557',cTTimeMs: '1000',cMTimeMs: '390000',cTplC: 0,cTplV: 5,cTplB: 'cf',cK: "",fa: "\/doi\/10.1126\/science.149.3683.510?__cf_chl_f_tk=a1piCQBQsovS5TF8GIe_6aXhDykwqetHSnns0L1Dwmw-1732712557-1.0.1.1-aQNg.hlbOOgIdWdwNdMXso2tvAt5PTArCvungYSOfpQ",md: "4noUU_FPw9Q1C624dtVTZNz.Xdb8g6jdbOQncrwXWIA-1732712557-1.2.1.1-_0eG9dSL_p9e.60BRpHE2V_N_6lOatlnIuVGUyPW_r08F_02M2D2By9lGmCuImzaHUwqm8qt9SOl8gx_uvz.Jar5sceCwZO92MWZcFw4EqSlVAicTRhWmR_zgZPsIk.dWpEegUo77Xsfq..TlQMd202_aSRBQWrI6o_a1r433o8Zm_SCurq5oq_quEf.SeSfO583sUlfPSDgd6X37iFibVC7yfqZ3D.3.LcxfmI7KJ3C7P4gKz_Y5fahRu9ngp9uO1gIqWLTPVhetPB.EPiJFNtH38j12k8C9lAxqucUIafXYpjFW2X.nZPhn4Ok8LHvyMtBCzCmFVM19f0EPwpNZ6mipzwFg4.bEr2_dPeMWrFDOYDJEUV2DviWYmoz8motCynaBuMZisEBFP9pUCuX2bPKTI5VK5bG5PucIfxUl8f.Ru2LWVxgFA08uw14gdGncQWSNKTFPR42VLvkCOJUIQi0ivxpnF_6jX5GRuCwaWwBCTMIuGwvSUc4113I8hPBzoTS8.6ONkwja8q23UNlXbKz55t9sM0XpwAnDDynk7DnNAAzCVqUun.xqsiT2TR_qU8VW4depM5Fx52ZuMI0kKfAMrZAuXYrnJN8ql842w9zhQmESQprOH6LheK1Z9o8PRXUUoAePRN6l_i4ivGQjmQmmIH24GOavvZlwpgfJTepZhjwnYru_5KVN8LBbBPqDXOTgVVOVNOTz6fDDRcxueehjZBrPrtwawBGGcyIy214MViTOJ.IIKnT2WgHQi8EkjoDqQLdRs7xsDWirXfjtjV6HWc2UyZo8hRtFqLis8RmceIUiPt5ZdXRtUpaDlSHJaDm1SrGHDCQ_2b9P1h0PzSN_6XDVrwMTqcqzBBSA3jgtcGoWlQmYIqJjwxuY28E4uoZFIS1X.GYLpbc300thD8FsOGxx_NtwOpNPHrl9eCzOiTNX5U_pZoD_pHOmJ8ORHn.zVa.wZkY99P7lhMc.flpBZxB2eWbe39CqmnoTtWOKN.uYejLuUSGTdcgqLHJ9VAQJwUXSf4Y5sON7370qJ3jo2CWU0eKavsbJDy22lj3d1leas.nBZWnN.HcR.HTJ0gAhnMgyMvU_NIJgm0TinR.7H1EnWUe_4NEbxKaJGQBfgHU_76Y.vSqxkCj07z2jR9U4GjM0Q0gbWyaryHN0tBrJWU5d4EP._zUrNEGs2gqIY3N2NPVFgde_lx1RmdCQz6AZQ4SbDlPezthyjZtM2VnYH_Z2V.RC1_xN02lzNX4dtNuR07SbrwLBTafiVufUAEDJrGXaOs7mefp34miSvrYvcofNVDzevfIZxjyj_xOlrO3iCiStqGqpbZg31lbr3FhrDeB19JAqel6Dq818uNsP4LajP24CRX6aRdZS.nsf5f_eqEJ7_.gUTI8mSeDSxhO6UKKgec_Cu87mbExahTSLyGXh_I9qzClrzqQuvbyUfIf8TzcRhk9pFtPKKF0DKTqefPAvfXg_1AvUd64uL6UYt7NaxkVL7UnTW4zcb6QXrN39rCopen.WJXHTA1mmyzs0jnL7G7qkNTczKTnEw3YqFrUWGaq3hm.hiSvaJsiyPBTYMrz.RoICdZKBldIpVY79ePd3phNh7pA.HMKEuOsH3ewb3UsAeshKLxsPXeJDZVsitfdnPxwrooQjhV1EL6ipiA1Pm3MZpevIX79CHDOyfXaOFZLSrPbQrJgpw6.7c8JbFLGBXc_8G36jBhLVWFtcEA3R6XRCnYvUvGSu5x3SvCiDtsQeH8LmTXzm4xAjXlidpWR9efundxi8Q6vcSY8C.icHVqbUcqImpjatHR9pR.6WTfuRHSaY7gbEGTLWlcSdha2zrC1sUF7Lzls3iTpdGSuQe00jchgIWrOr__aCszMRWyD95pukmBmCEseGtSCrJY0AHcNLst6SLx3TU2n6wLSgUc_utoKo6clz6BYFoJ9dN2092AYg3ntk98mQn7AFwZTpyXdFGs2TSWyJeSd6j8pZCMovsTm10A_aViMT0gmR7MLwRKNu3yi0UGsCS4CyxwzzQ.br2md3DZB78R771draiiKJuBP2gbibX_FEz_sbVpIF8UgWjR8chz0.NCq0txYB3LRcuYZVpFyNOBO9Ll48jXTLh3yqTHpNBbnCwYdm_2w_5inKf2u0sjnloVHsrYvrOKYu_VU0WeL4Z8gk452b0lPLk4dMV7BJiU2ca_9LBKP0iTL5hMCFTs.zUoGDqMGz0XUl.lZLQ1TKc7vhiVeKuI4yixq3e8pWFVLg_sFLM1n9GEqEDHNTS8LCc5G3KmNuXJGip1XDoS6a9sK0gwnfCWsqW4226mNYxyp3pofAmUfCeoUMvLcpArQ3hL0yLKt.RMIybviI1oU2TIDhHafOZokfq.Bxf.2z7PaW0LH55gxPCtUg48OcRIr9KF_w3wk3G.XyRRc7IeK3n3M3DrVFVbRA8QF9Y0lS_sbz81BzvzDrs9oy7TZDSoGNnVLX_ECfJnnfOxfNgbDiEnxAdVPsuI0lzHaB9WGxQzr48LZPH409JvvHiSuLXWmCputfdkpjZVZwGPUjD.IJwIWX9jZOg4iE2IPLRSzQXW_DwL1VdHSIt8ZuqaMuZ995olZhnNw5djJPjWNdLAcVMc_LOLpx0s.CBQ_Nd.O.Wz832qIzijAitHixKPUSpor0CV1XuAcRcsoGmYpSoN8ISeoCNmA6hLvr_3BMXYzw3maeUBgCdGfgAf6RWjTRX.lOc3A8Q5gingtYkEpkD_uzls5gBYAlz0IDnzG3uUcTLDeZ4Csi4JUrEDhDreTtt.cPovcnH2gUDVy2SR5YYEX7UnrzlZ0avHfkX8CqzZ258_7_Yrnuzhxgt5a_IF.QlRpMMZhbCgOLj7DXDE4_JHeYptbqgxNOG76qHq7uySf.rlf5yyYPlYO2l2R.L53EzISnZo573vs0GrZjXZr9N3KcQP4h_vIpfVRIh_3XkttDkoUfqQ9X9NsiWkOEp7twWd8qeFY5LCGkdAoc.HfEbK1",mdrd: "eSBm9snn9y2DmwuNd4nNTFwcgh9bMrgABhr3pApAxHU-1732712557-1.2.1.1-2I00Q4g941J2JfzuWLNXzLn3OaCHgm4unFuFmaQ34nWv5nYB2ed6FJmf2YUljeTSrR3YHBDcy6KY0TvE4rgvujhZOEDrS38pJ_HwfU9P7YCsa6c2TOm8T_QprY9nDvYKqqEzwV022dWSGkuKZ7X9oLsvbSKwj_QJ4BNyNzCDUWtAKSbHX3Ck3Xn00uhmb4vj2I2cvt63T0PZI8HNuVCV_jcIApbZ3ZsoZtdfAZVT7B_pjCkjHLfsxcov8K3CN2b6d7I1aKrgAkbW4cRmy4slPdLkOqL_5KX0CPWtV06QYKcmBXFOy75h68Xf_WTPMMkXX7aBXGCzFE.CuHbnwvcDMOOum_ktBXa96EkG11U0DOgs2B6633oQZ9jbFqCAjtebB7A8zYw0gxfkEJHLR5EUtZJ8G56HZRriXVR8wXXXSOxbrWQRzBaT5YI_7sfV8wuMK0MAq1VDZCz8Xej1YmvlG5Dvq9TktBt2rrSYalAuwgEWjX6FZJ.KYjTw.ONOvBwp1ttC8ie08o_vp6m5lWE.7Dwv_tjVvtap2EWXWtYu6j7nJCUiaR.4ZVSwr5KY5vD4OUDpf36mZXsjshcekosTGq_Pocm82L4Ki.tlKGAXpTMbXDnv6Adkh8RhQxLJqz_uCxGI.mgBQjqlN8JA2YfvBFTEm.VOew.aicKFcT.VA0SSVkz4B6JwgGywFBZcxvhenI0nYLlEl6uygfT_AiulX2K8b.uHNhNJllFfDrK3tT7rbhqjSEW6ASMdU9XunI0iLNcl3ASCDjzy2IbYite5fBBOOJ74P2P8OrkEsxmfEOWmw0GQ94NvjU_W_4ElmeQoHT1f6Vm_y96iKpmfCwelIkhEqzc8IUh2_zVo_IkDkCf4u.LFOMATAx4Bz2oUwbviPk7DCxih.dz7cp18MnGSJ4qgpPuSMjaZHGxfSyuYHkW4EkTzj958wG_NR9BGzjF_o7VWOd54z21wFkBzQT76DlRm0iaSgHGebIPMXgzjaNSSaZv4eW2FU535SqlaGYvbSdMqIoQ0rOw8WVkLosvTyzc1UehftDKT9WGYIyXjO7X_bZauodHpH7Nlt78vyPfEtC7BxGNfs1F60irkFsfpLxErvk4gpbf6JozAsCAWUW8oSpnHCth9g6fLVZfApHQq.nO.DyHmbefJMy9hbqCzdOug.S0SZx1wp_6QqW5MNqcxjjFbgJ.yp77Z0B9xHSbTuxwsrBbaA7TP7ICQDbZN45PUXQyi7OvnM6eRmlcMcXbGHhjPNyRalagXJtIXIN3fEIkVwSKaJ9eyzQas2Fj8DxT8Qp6wMrIHbRcz.PDUdBoE2O7WlPlQ3nMhq3bdUyyusR7puGK5883kmzpgfdRI7m9BIcYv7RCoMdRPp5r505JeV8mJBaLGo1y55_f9pB0edDToHfaTeegZHISgp8HnHVXdxNRgDuCt3XPfFFuuSL3vITnRT_cAHJVAl4pns4f3MBQJKgX8XzulExUYGR6ZdQmtlJo9xEKmSGNaIcXnh8YQC7jlpnE7M7PDGoc9e1fZnHlMkoEkdpgSXqZDvRRfnoWFVrG2flIFGQ0c.IxT_3AMxR7KjYGddEhkQECL9n14LeCyHmpSTYsLtTj44lZPDt6SK3QrHqJcE_LHoe.iP7YM6Mz3i0MROMKNthDYTCOR1LSZ1aB3EFwkpRppWbmrQbzmQA6ViN.sM.TJgAWI1pof2cp5ptrMoD0WLqKK5g_2UOEcpbJ.WAGrxU64dDJ2wlQo7F5s970DW58kmkPjmBz5ZBLLcfkvH3R4RYbCl1PtS537r6xr3JnSIKzVLRmWCWISFEe7Ipm0eMxV9NhypnzY.XafmfqGFDE4SKOrpU9ngeUxHKd38Jd2hL2hDUySw_fvUf2rF727T5idW4GYSHCnlWqVtK8DJ1DvQ6kweKL1jPNZP6cYmMAYNF3rTEfhOe0LtXyqviNg5l33Vp0DdyjfX7wzSd6BMqdVagLnJO_l"};var cpo = document.createElement('script');cpo.src = '/cdn-cgi/challenge-platform/h/b/orchestrate/chl_page/v1?ray=8e92504b5eb3ce59';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.149.3683.510?__cf_chl_rt_tk=a1piCQBQsovS5TF8GIe_6aXhDykwqetHSnns0L1Dwmw-1732712557-1.0.1.1-aQNg.hlbOOgIdWdwNdMXso2tvAt5PTArCvungYSOfpQ" + window._cf_chl_opt.cOgUHash);cpo.onload = function() {history.replaceState(null, null, ogU);}}document.getElementsByTagName('head')[0].appendChild(cpo);}());</script></body></html>