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: '8eae6e9b1b4dce06',cH: 'Ed.BswuiMI8UntcnbaqCG5LGhb.i62DAQyLko449zDw-1733007400-1.2.1.1-LXacVvfCaZ3DPCv7nJyj82wgXLxg.o4jYJJQA6rUDYqUnDBhdeIZvTCxAA5GHCxb',cUPMDTk: "\/doi\/10.1126\/science.1221748?__cf_chl_tk=mQfz5UTVYWzd64qdo3TYNTF_4oHW5EdbUDEYlBJ3F5A-1733007400-1.0.1.1-uKfb6XHZfbz7QszPoBsz5axR.d2CiUU2hPDojPB.rX4",cFPWv: 'b',cITimeS: '1733007400',cTTimeMs: '1000',cMTimeMs: '390000',cTplC: 0,cTplV: 5,cTplB: 'cf',cK: "",fa: "\/doi\/10.1126\/science.1221748?__cf_chl_f_tk=mQfz5UTVYWzd64qdo3TYNTF_4oHW5EdbUDEYlBJ3F5A-1733007400-1.0.1.1-uKfb6XHZfbz7QszPoBsz5axR.d2CiUU2hPDojPB.rX4",md: "FBK22A_Dou5bT0BRk1wzpTEK13IY393MshOfbZkjeMc-1733007400-1.2.1.1-2B4S7OXGjueIEcZMbFudwr2_lXYF5TVQpii4TCYGuMbEGg_08TgnPz11N6oDwdI22wdU5qsHIItcsu_ViyFeVkmPq8Gdwt8g2u13utR3mng5TibonPe5X8Y1xcXnWnKMWcEKDkHJy4TUJdp.Y4QkB.z_JHYjJTKR1A94C0fN6QwgQ9MPcAqrOIMCHhr2tEsk.LvhydyKqqV_c8DDxCN6_H_s5YJ78lg1DAobl1QBxeXicOLwE5akVPhhJpK84mRpys3laETTcsQrduB11iyM6GdTqmxTaiA8Hil2AGE99L6zT5rmfqm5tSLs8eNAVDBKLG5_46TlqZxNT7PpDqOy0Ezrdq3QT3fXji6F6Rfs8fh.r.R3OfktLaXEQCJjFv7N5rPtEoL7nTAEA2n74cIYdlfRr1NPnx4Wwum9WPK7gBUJwdt_U6av3_.kJya1SaGMP_ZdH30Z2x_GTO.TJ1EKjQmct1m9NiPzPNdP6nx2HbNfngeRA3CTCcTSCG4CUFq0am5Z1WH8lDVJD5izGI2GHsRCjuTgvpUZMrId3arfdS8kTZ2mTILfSSznL3mV1e8SPHZK2P1r.euid_5U7hnaZaYzm79PMD4CA7kTvaeENAs9nM0kF0IEXHc8MQ5JAQuiPli22gv057FwJAthQXEef6I74vJIRiI_i23vQ2ZSOIx26mNZYGK2T0UCjEXUaNcgQsDcXF0YDDrEGYntuCdSG7gH0SCNBslhJgYlCy1SYMfH2UysQ38b3_9PKWKlKRo9u91q4gKoq3FuOAxLHRAFtk_wJVVtocgMckCnvmkzWWuRJddYasYH3eJ13Y0T0IX0wgAdnfWRS5HyzHjKG7AMP7RqzIslp8.ut0QboexbNxhPlnsrFls_C28By9trJbvisiizm0U6yPOoTr5kgMOr6DrCj.OJdPdrZ82pBirKMyCnT4doKNwAbKI5t55xzbMgAUVWT3OLI_NA_saoMwIJ6OQemqwIj1_n_Z.2FNMNjlexCmM_tJzXKe3o_vw7jS3RyfkNoejhPknfQT67kI2rRZU89Unykl33o3Q.mw2Yv7H33Aa4Pd6Yc_hsvCURSgVc75muy5uCKTbs0iKHWtbSb_4tpcaQlb4LP170eIHH7o1vNiEDJEdMMu2Tx2rezFSbwdM3InmyTUhAstm74IGWCqD6MA5KfNnYDET16uBXqg6MIbyOBkAKlMwxrB3TvYwZiKrs99abea4cQMLPOS3l6T0C7nvVX9r0qWNZEt9kU8Uyy_.DBUzLPiTZDodE_kMkMHSODXs6_rC4c9NGUVJSLn.ABdoB6ou_NUe.lcCqwVkxUC4zukAS4nK85gDel4eBFXNFYzv1ogrpMqCwSsULRNhXumUgP3WtOMEdwj5Tx9zaNl.n.gQP7zTVtdneJn2OpgAk4gMRs1SXTk54BqLNfwxT0BjraHEL8HTypMecQ2JLLh4U_JRSwgGgRIt8Ao12Y9eZ_OSeuAy6ZcLZiV_I.XxiaflPPZamxSpnGk6X8AulkTfOdW7JbruBTkyRh3rJaHrNb1sbV3YZsx4i5SWUDRVQ446yQoOGkR4XQHTETtYQDJpFShgyN0erEfyX81fxB3c65KxdlYXMl6YaVD_EXjlnM6cfXbPE976_O9D4YGqPdlG01jQayTZ0fMa8knm4P2Gohy63OiYfA47jd.PLm5LvrcbkyP.meWZra8TPQxswSuw3QViMWWplcOsycshbH7RSpyv.9SUMJwBGJUriR02OOI6QMGjAFpZBh3D1kVcXxKNgEECo.Gbs_C63PqYK3BxaYizh3ow2S246cCv5iZnyMYtBGYjuP7dmaItbdXFYNazb_RYJQoQYDWRkGoZ_0p8WlPecIUrb5dGGUdnrjVbKqfeGq9tOd6h16aR.Sd77XJfcpnE3Myf0UmkSGVWLBTYyeI0eoBK8HTI5LWNLH7.yZ77QAiCULS4X8MXf6cdGwnNrhNqUPSs8SSAhmZlVyp4BGcyraqtWztL_vn7OS9okv6Nto592Ng5XZmGBVMPN6XG78VgEVfVyIRY03BdksZ9SyFWRKyX6iQInKpQIkpNxd8I3LnY3GZFLsQ4K5RNNzV.jLsf.lzJHybg6kovrcTlFdNDYWttuyaMT2zGDfz0JMF8vdTL3azkPqc.E2cp_mwSSNtGHqMol2PQMUg2OUYZ0.vD2V5tjJYG.jZuvyFaJRbN8QLSi.ZlljddHH_6eHCOmX_JBB8etlR8LZIjNWap81RDObtRRgyg6xhrpmIyaq0JM8h9e9SvHzRO2kFNdol7LGLvNXx_a8u4Nmnfr7SNQNxknb71ZBn47JugPlbyOGJBvmMERpDS76U7AoOOnJ0Fr3kIgECJD7K6hC4YAZeyD8fZ.4AqxAW.W3dSVscYP1vM0zSv5vYf8k_4BhuLQX1_g3zCGLcEUncIYAZF9LQorBnPNZCqWlerw.R133JbHPGuKgk6G.nuQUeZ8eBwgIR2aBrCrNPFq04Ij6qVLN.F4rDfYY2BYc96My2frMKxsVAYgxVAGTCZO5TC4pAUQwRzjxrDxz7mZoUqWBa5exKyAoypuFOhoe58ecB9Eg46gQo0RIoB8Qy.R.y7q4CKlkwf3KEBXYQXQot9gpnV_ngPiySSVkJqSFWatLp__3cexFhUHWWNcc.IMw_.7Ax9RlP4uexhkGrHipTQxOH2q4TFeZRpX6lmn7ktCtEJh7B736XDR6L7OD_97newJ3KO7t.VFiTqDHceMmkAwMdp_FAn1NiuPlJB7E5K1Bt_hr4up8dhXxQiixxu4YMg0EbJCvHxziHMTdp6gy_eHX2towjXiQAAsfMaGenAecKf.OYx1Ixh8RVI7d.n_l0fK.9rWIgDuYjfC6y0rY4m.UZWqGb03tt6KTfmrpQOJlYTpNAE.GGw1jmES0GMFJUP7CyhwkSGJTFyI_YCG6cjKAT6Y7_uxOwTLuGbXLrk44AaH.IOK6xNvDKXjvbTqXOTTVmQ",mdrd: "0v5129Ax2sB1gvHqPuHmw9O9tbwYuo0hZIQiKp59dZM-1733007400-1.2.1.1-.PVdB509Y8ZBzZrFzKqWscu_QevtjDB6z3QP0_VyhRKECYlsHDnPaL4ZTkF.CGRD7K6ujRJSNmN6ijp0iAGOl8CYRnY8C.t9viPgdXlYhxfUpHr6QSTCZl2Z._TNAf1h0E7KLdY.VHfSm6rbT806mAQ2kNdiO6.GsSVVPJQSuSG7g.c3_o8ERxTaO4iqAQPPzgpIYJez8Ol8v8Df1eZN3U4m8T4RZOB5c5une0QuDPOIdoXla4.AUgXQQxSTYSJOqoE08xW62jHeFkjMmia1VmZeP2TS6VBi3jjGIHyUCdPa66HxxvTD2XnpU6aO7YjkD6xhco6sk.eqws5CDagnQbcNb2inmHBNRxXu.QlaJg6plo6olJHBuKtSyYncrmRfi8oVkhrXtTozIWrb6QWGUv1Qzp7XcmGZ5Yky4V0teZMk9PM_lalUrQ9YR8crFLLOkuQu1s608_mHuihGd2Vyje_jVSEHAMFoluSdMFWTrGUG1Rf3GNJUPNat3Wlc_jHerbfWK3S0PSixdWdZQCGn9CpBWIu2d5MQ13szy5aIkFI.8JD5qVhANPJ12VKh8MFQeVOgnmtSUuznfxoXeUSel67S1jgpqLy..b7_1B1E1EDxioXskGCnlWK5j72kxN7wF5CCZkyjeJns7ySa_Z6KXO.iOmVys.AFLIiYVSr4hU5Rw8tAix1Lcl71Gp5PULrj.01HdwvZKEylY2vsCNNxX4hGGDdARvB1BG4j92deyMLEPKmo6Vw96ZQop5OPl12aVtQ2Aod7Zv7FWSLfDGSNpApuZG.9i13pOiSDwJHEIja3nrAqW6vo1WH8.pK_FHfQoHixIR__hB3w9fomav1eEpgR73QDZmq_FSuI_CS8Os4OaUU0kMpyV0LlDUJKNhK2sqg_BtaemKo2_0_YbG4_WK.tDkWAFSq4ODY31rUQ_BJhaXSVANqiL3grNbWZnJjPMCOmNXv5qNYCI_DX28PBhVLsJap1paxC79bOE0LwxmMlsbNA7GvTX_UAmDqpwNOcZJX44qZEeFFtQ8IIb1DNAIyDHl2njiYOff1CLfCmKDwfsbGAf.ZEx_LN2oy68bsCMJ6suS2Tb9CPhIKbkY5ujlsiPqg9DFtGv0UMtHRgaWp47REwsgebzjWmJYbFh68JaVOL955UgvbT3peBpiJHjcpD3BQ88ptdXKmo5HKbTBrq4Vic6qERBpa2m4M46QEK8fDszE.y4b_KENDDkQ_D68PiCWIrVLxvRPgwvt8UrHIU6B1VnBtz5A3eCsoDrtbtSljPO8BgsVAJv.EVPaqfc8Bf04TFSfNvh90uBhlXxmSgIDa.svnFodepAWv67I_JQd9ys2ZuLdlDaSUn4mymPhtWG317PCGFCuTAdopihcMyW5xU7uxyDBIMBlN3OUljLX019Kvol1sK0rv3NQFvid2pKCiSAfzgXVTPls73VJlijlYNcwh2pobvqysICq8ZT4gQ1UIZsfv1gurbkp46dckFfG_ikLO4dwGOgKFZ9OmWp2v5T.Z97BaxaPV2fbvu3RG.G7zRsqOZEAUtw4pWzT7H3iPhdLfEPKy01ccyCtuYR.mwOTj2_yx7z2Hts7.BN2PuEXuDeJgqR2vxdj36GCIZC62zV_Suc9xJdYxCy77Aapz0gdNas3W7r1T73uNLlWPDFsPEQbvDMH_nhVkDzxGoSkQHGPYT_7isaAuFN7myOORjVGDgzYUlOU7U4fzXjCEEIDk.JdACouo.qV6hb1IBMvdJLVvom0DZMqMMkOlNGqz1dcQDA3GPnQ4bpXFdWzflgw7ZpONR8vMnGT8e5wKJcQ8tqQBo7w1pq.liMX_7MjMPndPDcNHDiDMg4CIS9Kkm154xyEypD2_J4MO1YJ0aPfT9ifCJ72mMMbuEtsdKA5QCYAkqgy.hIqH.XYbN17tuNsm3hFUiE7ssQMy.Kkz9RW6WE1NyegwM9YOvJPk"};var cpo = document.createElement('script');cpo.src = '/cdn-cgi/challenge-platform/h/b/orchestrate/chl_page/v1?ray=8eae6e9b1b4dce06';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.1221748?__cf_chl_rt_tk=mQfz5UTVYWzd64qdo3TYNTF_4oHW5EdbUDEYlBJ3F5A-1733007400-1.0.1.1-uKfb6XHZfbz7QszPoBsz5axR.d2CiUU2hPDojPB.rX4" + window._cf_chl_opt.cOgUHash);cpo.onload = function() {history.replaceState(null, null, ogU);}}document.getElementsByTagName('head')[0].appendChild(cpo);}());</script></body></html>