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: '8e829b3b8c6bce2a',cH: '5eXejb_9twIQjxp3VtkI6MtL5OMNdBdewbcYiKhzHBY-1732547854-1.2.1.1-Xqh0MANvI648UzFenu1IhG6q1lReVlbm9zWULUPR7waEV_U_c1gVz0m6QxsmRl_u',cUPMDTk: "\/doi\/10.1126\/science.247.4946.1043?__cf_chl_tk=lhMHNLqE894qVgV8sLxtdjzX2lelv8MElQ4FAg1c40Q-1732547854-1.0.1.1-hwsDFMDc1ejVviszq3jNR8QmI1i3yfNnft3wVnrhk4M",cFPWv: 'g',cITimeS: '1732547854',cTTimeMs: '1000',cMTimeMs: '390000',cTplC: 0,cTplV: 5,cTplB: 'cf',cK: "",fa: "\/doi\/10.1126\/science.247.4946.1043?__cf_chl_f_tk=lhMHNLqE894qVgV8sLxtdjzX2lelv8MElQ4FAg1c40Q-1732547854-1.0.1.1-hwsDFMDc1ejVviszq3jNR8QmI1i3yfNnft3wVnrhk4M",md: "RLsmLGuj2teTEG13bL2X8wFYeUXt552OLxT8S7S4h2I-1732547854-1.2.1.1-tUClxsjtt.5wxTmJkPhyDDHeGOho537gH.ytTJhkhvYUWxcYh9RjBeDqZAFa7NWAOySCy3cyVC2TyMI6P3Tumfp6z82xijns7WkFPHd0V2hz1R3V1koPXE47F_r1JdsM6R3wwUC7zyI6XlW0ydlUXGosMUI45neFyLYL23ko_N4uUskynC._XdZQopb88VVO8I9mUdrT4AXnYf6xUbm2LA7bdOdTmXcb6AhYwxDgb.b5wSvoQwuRvVTdkYrDki0Y5iZDua1YCyFJfZR8kh6csUefqAxrAU0hDV1P38oRhgj3SZfGq1s2Ss_Zjvf87FtB.zftPjPTGuUkdzyM9Oz0RvDe82xjzlb9RHwjjrDaB0pKIFSxq52dPhhoOCmdj6z2NV77OGucIaaQbtNMl6bDYzyLGHOL_J2RChPkE9hn7rJmLzV2rD46ElZfZ0c0IZHSR0T33OaHGCh.6DcZiUMmZWc2sjMDv2W8m_i3CboFyNuFNRpnQP891MQ2H95l6BWHAU6A87o6_0UYFzE3P9wyhMEF5GP86GNAc0sSu0tA2IGksoT2u1Uha6h815MB9pDqTz9Sm0wAabbnMsDs7KH5F6NpH8uuqgi6y4BCMHdb7Ok6qe6HLbUTxGlFKNp9pjzE8cxT5Mp0YdAiPnTeGAqxG.Vvm2A6CdHShhqJuEec8yJddOVFFPpzkTTnRh9H1e_jG5z1Cu.3sdIzrgSp.dKiyODQ73qyqDW9rG2dUout.YBRR_F_ZtvCrgGl89tDqLsW1Q5zNrZwPA_5H50YWcveN6HfjcB5U7R674d_gfLwI70yN09zfzdALDdtCQJ31sSgVTUUrGGyun5QB5zugH4I2h2m1DLAhKZ8RCcR2e2IAKBBC.c.ujqNEL8a9LNw50YRsXmiJ0XOpYOsZzZuOvrN4N8ARyNi52Nax.K1mJc8AinZ9MP_G6GegV47ywCS0xEOMdW6yFhwwRPb0.STlSlj1q6pL13x_nXqY.eDthAhFVZZaJtp8U.G15ZoYvIzBJGYPedQp88Jlt6gPcKMZNiLat8WvO4sxl4wD8jqqeCLzft30JLQneaQrhQeflh01QazlvNjx4ExN_bxn0yvcmwVjb7hnRlrm279mHBr7Q.X_3wXwuJxSFrR6E_l3j4eXS8ZnBvkbXmPS7tZBglUDXjIkJtJY7nnIm2vbpLIyfIeNlUMTCQdIFDSxFC44M4FovOdSCGmPQd3H2iROT6o3Iu21KJhADMfvSgZMGEgZbFHYdZzfx9YEFufZw9qcUO78th6.0NyaT46XX.1GtwA5.1xinuxtry5AqOBrbcElMYBJevIZtmvScmsUB.u7wjou1DewXutSKM.hOLjdKyPa1XBouA9TQV5BEW5bSoJus9lo1Zt4YfWHk7nF18bB2eOwarxTICWBQNt4HF0fCRtX67X9xcp4_P0F2tvRbVl18MK__fQi5Bh2D7unGBWhWP1GmZqUGkbqMbczpVfwtX9Y_PxgoT4ufsfgSLsxjh4ws821h1oRBGdfU06FO.qv2frlswhT5xlkU0dF2RX2dkmP0YFAZ31ndCD8acJ4vjbZ0eOto2VGBCUZ2HEiKzEdBvU2cXnSsZca3rihTf.XFsF9iZ_RyJB9NSX4KWkD90EF6SaK7ojLzkg03mcPGcEwMiSDyGn9aXLt_jzEp5_HptfXLmnXB8g4DbiIxCGcNh4OcNYsihwmHU.VIQm_gSwQo4Inc3bCqRRmbBGkjJDja4nHSHnxW5DjkSdKMPbfvofe0AUzoPxLZuD4s6hHJYdWsXRpYMpvYSIzhSAbhG6N95W4FzBbYLXPwz08zEUuc3Htv_pL7paV.buZeZMx6bXqOM8jtDeElJEBvijhBlfBbOFevCjGgQVWeCxxrLuNNbr_Su.1o2ratRSkFDRj2ZBecBRBE6g.PhmPJ4sIKi8sx185c0wFMTTy72noD_cmfA.YaZMPDGixnsn.rjx73jLom17Us4D.5Ha3PEMkoFZZFvsA8Pl4M.OWY.IajkUAtRAnFf8rUdICcwUjdjNsHgIt9D9Swctx9vgQTKlSdHUDgyQy1Cf2frpD9ZlqOAaMV7uGd2bRAIw6EXHhE5VjAAohWkSiMaIBcJnd._Zd8rRCrS5FMIrymJrMWZIz_FqYdB.CxTL1Xo94nHpXvAuWzONQ6vZNOo0auc9xjCz.ObZ4QHFUfbXKE2tgL662PsssLX5uyrU0J.mKtbgLlt7Z80yRiWAFT2FQD851GFaF0zGpyTCBUx11zgNgoMIAEry1sEvmTECTsBwrDG9vLX1d8dcgW3dG9Ne_lGiM8.qJoybkSCDcErr.uvKojnx9syXQ2p_.SiKUmZKeUeVFiPBl5hLjerZB.c8avfsyoUG2VB8XmO_L3lJBJoaS3kmMQJJF07ZScogoQ0hTjgd8ODrgjczKhFTghXXSmb4lRvWbuRWHuBgIJOhVkuDefWLDykQbIsLwQL.fguxuyJgNOOmHqBxeR42z4ibrhzaNLSZGI71K6hVBiHHcBBJObFz8H_XEBezXAZkRmMUMMmMr3CD3QQ0sibVEvd4Qnl8w84QAtjYIzEw82an7b.gRlMzzssp1moSThNsd5cPwuvy01.qhMQBhIbCHoQ0vuvuSOtVBiF93CBuwMC9uJhUVAIajRLuRGNPlPVOxhdN3AGpiAt4MwsrwzwrKr1XS1U13M.Cy0nwl_pPCofFyQqjVXFM0cZRuzk7UAfY632GHqbSnB4FWsdGRwhDVp.39ZB8MoIxDXi4HAxjCUNtEjSVITxXJUqcNz_INpgR0HxXJGvrd_s82XUiSMQ6dE5vq3h.9YIgLSe0wRZ8Yhv33gXH18B9sOrY.0V1TBQSztMaAesk8_keM93fF_Qm7IHTcSFu5p9uUUlzXurBg.FWQa5XtwzcOM_lcrfVSF9XSF5xG5fcOTPqFFKhBp0ZSJwMyk15nTPEBefulba7_bsAf_Fo1pR5fymw.adrmjgkvxh3XmjPFMlIFkbS5tK6CySK",mdrd: "I1CXeUtqpHEOCKVLRlcYRz0CtV50CKZuu3rQg49kCi0-1732547854-1.2.1.1-lQ3YkvzWKolLn4n02KEkbZ_5pLpT97uc207tzS4NXLgA1FsLg6I6vxS9YEVA3T6TZFYmzwfzNeJY2HUaap8VcxlM3XkkkvedZ_CpW15JgCpJpKKe30xB51.2qPKoQBUZCHl1ef2o8tKLgnRRa8Zby7o5gmNHlBNtT6wcbimNOeB2o82.GRp8_Xb7UCJK43HjQRZqyBVMSJYZDbWGvdR1zkwMiphiD.ZwMp4vGZP8Wu1YetW3TB.B77ikktZv_FJMRjbrrewSpuHixLdsr9ug6I7_CXFHiZTCOCoiON25OBgys8p5qvNSsnxN93O2htK6GqeY.J5Yaru3v.3xhtCdl_0zGgTZ.5HtW3jXtqLsDRbhBoXmmjDAAVbmpvyH26lYTmzpwK5ndOsGqtPn5GBf6ugJPpJJsZDiGcsMErvvQTUpybXK47CfhARHYJwjvOPUYOSeQvbYLDhTmlsdW_on6dcxpnCFIg5aOF.hNpCsTqRqiBGp099E6W2VdtaimImy.eXBBQYeN3L4uh6fbI8cXzZJRg3v2RUKBHJ4AezNSgPsG_BiJja9K6Na1s0gtp15uklSD9FWPokx6YVZzwS2eOA0Y2.9vxRUHMryME9xJYZMdhc1lehUbzUxz7oYKRlCFIsdDe8b2KdSbm_NeYnWauTJcWzZki7EEHRB6r6WjXh.F9gs8Qs8BnYcJuxlgfPvbuchMtEcUNlOxxfaPRKhApvhKHb.wQ7_zn8g2slrNVR_YkSjCPS.UP5qqZwcXouP1w28KYTjOj9Xuh69BuMxBP6qPGlIDpQTmyVJeGhUmXTiv9LlRTDsY7LtiUTvv7GxIjSTuQCWdny8Q6nKgI3ea2WbWkdGYcbwSAVegO9pYhhb9Isck71dU1QN64_sNYi61B9kZXcO8rE.69b0s0Y2.Pb.oYqVscM1X4TiKiirSGTyac1vldwZrIVkogaEwdkR7GJDAqZMueE1wNyArWKZmENEqjgnLR6K7sJ9vouPfqvfgE95qLPcW6O9AOeXL2hwI2aIo0jcZDzGuewU183AhEb18U0efJ5s58KddxqEFx7vRm9Ht._W0QU_tQqwZbOfbIdKe_pITpnThymdw80QsRLUyhW3Q1UOfMKZVqZVP4HDiDFke9KDKjcUlGX5xpW0mSuwhCygWR6hDRWdCZpFycEirSjmumHmTTDxX2sZ5UTJ5KGLjKE4VsKHph2pGFsQeRBeM7EYXiSgVgLs8RYs0F3P6NpfDPFAX2y_9r_TdmC3E16aGnphCiW44.WoVrtgwSA2T0cc5vmu6zsTzXtVWUZP9V.0OSiFIYFNS4O2YKpfZfnLUJeVs_rQejwN7F3Ue67YmX_bz9XgyM0YauOUM4S8zzN..obpzOZptP98hxlr2YEMZiwUhBdezL1q8Bz481v6LV3Hp_0NnrIKM7wjY82DNawZlaRb5N.qqEFOQgYUQncHn1n0h0nJVgRWJNdgF70b.Zwn6U_9bVF_8w8oNVQ5ZE3xA.nFz3GId4UgObK3_nCa.EoDL96zJcm_rr8zsvUuagvdxUbRcBtmWM0KH8t_g1j3sldXln8PIs7ALzsvbM_Ba4J3v1LS8WhHuAsfZNBuOdmLgjlgn09B_qw9OZMBaLM96i9V_vdRjetTsQrxlfQUXeou5L8aO7.l0eW015D4ARBH4LbVMXbJmX9U8gqXC7k4LcZh3nh_pl5k.SS4ivzaRdV7gm6bT4PS3Y9HO9iamDpvuT21taexJn0GayCPIQp5t8WErXuIvjPxCoIheQmfypSSInwZY0v6sgcV3QQ1ZS_KKIN8yEqjnB16lSsiM3UcB2RU6totGuoRy4EAcKv_swF5SHj3zEf4OzGRwV8e8uQZAb1lYAFrRLo6wFnSgqaTQnHrQrdXarS_BLUgZ_PUlbeLrcly5eD6iXAHNajDHq0K_G1VTFAGjO._8L4WHSt4_shDDxqiLLimrUFZif3yk4uYBx48oxlgOKOq"};var cpo = document.createElement('script');cpo.src = '/cdn-cgi/challenge-platform/h/g/orchestrate/chl_page/v1?ray=8e829b3b8c6bce2a';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.247.4946.1043?__cf_chl_rt_tk=lhMHNLqE894qVgV8sLxtdjzX2lelv8MElQ4FAg1c40Q-1732547854-1.0.1.1-hwsDFMDc1ejVviszq3jNR8QmI1i3yfNnft3wVnrhk4M" + window._cf_chl_opt.cOgUHash);cpo.onload = function() {history.replaceState(null, null, ogU);}}document.getElementsByTagName('head')[0].appendChild(cpo);}());</script></body></html>