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: "pnas.org",cType: 'managed',cRay: '8e968240ccae4022',cH: 'TGWArQXOqldnjtrDeAA0UBkZQyj9_Ag2sAdyPqh1CoQ-1732756546-1.2.1.1-8IqxaY3zgGvD4wbtKXqv8xROePcE1AUEBz9KnoznOTQQfOuErdJ6w9VC5dDHmLrQ',cUPMDTk: "\/doi\/full\/10.1073\/pnas.1012231108?__cf_chl_tk=uyEAa6ViEH.iW7UfFAbD0FmEHE9ptp_dsi76UjBtOW4-1732756546-1.0.1.1-CouA4GdVNgQLpCxK3UADCsdmfmFRQjyOlRXQXq70xlA",cFPWv: 'b',cITimeS: '1732756546',cTTimeMs: '1000',cMTimeMs: '390000',cTplC: 0,cTplV: 5,cTplB: 'cf',cK: "",fa: "\/doi\/full\/10.1073\/pnas.1012231108?__cf_chl_f_tk=uyEAa6ViEH.iW7UfFAbD0FmEHE9ptp_dsi76UjBtOW4-1732756546-1.0.1.1-CouA4GdVNgQLpCxK3UADCsdmfmFRQjyOlRXQXq70xlA",md: "8z6RdNLMc5v2l5_jNBKmLM1RBK9i6U82lOA.jQy.m4g-1732756546-1.2.1.1-CYBNh.qzXQQj2Hj9sOB29_0GRqxPC_Ebe5bJ_K8YsAoqFoVkSMJQytmhc403NR1uewUYh7Pep4oyNKZN2leDfVPov_.8uo9GtFQSS5Eh01WACg9S_AFSnPBOYDVq2jl5PiKnI.uduNArp86AiV.l1DrP_IFMR9pd6KW3fbXyH9RNE3WIPqclsfIEVCCWNe6gzE_7Piu6XNR34XYzjos7fnsrdN.JurMjret4wXXK_fCPUbdnrM6H3M1zZD4OsLnqVhccCgMo8pAWtZ.oSitDMjzaBhXBgSkVKwNUwyhSlAmxGRTiG5lTV7TslPBJ8N8Km94L2wVaqtN5oX0A79GlOLfg3s9fEXHnUYiESiHGVEmEfN3qIQr25bcm53OPwY_95Yg6RjPRoddjV3eTKt6LCZYwFFP40abRjaW_w8zqlsCKBVceR_pUQX8znR1Cc0Q.fM1ri7BIssPhAXPkYE5tEYbU33E69CddaLqpsyaYhbDxX.UZjSVhMJJq8aYanGgbNkRZXvtmC0kCs26lGWFofz5E.d0y9uH1Bh4.lPE0q91.lQdA2vOjXB78nVdizjh1bButzex2uupNljsgaGHUhyk9s6BLyptnxJKeS6qCM77tB.6ONTclOqoPJxHkFcK.5M.jTIRAW_4NFLs66ds_IzSKNCJL4QTFYC8ofRYwSOTyqYvm4vfqFTLw01EJhsRLggfrwCYrUxH7G83FjXI8_lIwgD9qBb6tqQBeo2jOuXQKG8B3oGGmr3knVmLAPkY56IO8hWLGjLxpbQAG4DUJN7OPT7TTpivpTWANb56.bzu1K9oTnaHrDIYtJTHDxiXyz1VvpTtZbD96Fna2X8ax1VTYBMXtEoft74bFghRzc3u.dZnVzurl6OAFwWSiqK7UM1.H37T.2m0QupBL4STjuGZ13H4kknz0fKdbyxlPE7cWafrKAtrXcXLSazUW1.0mvJwDkQHgkdu63y0FmTzZ_qznPrXteKrm5B0HxexAs.ucSR.9aQ2BsZWdoCPw5kEbbDvKaN2g0gHiHnh0NRn0yrkvOhU.YQatdDLx0ODh7wUcKNAIW6aS02tFkFTCJ9mDF_E4hBZMFVzLEkqLvIMemUGO3lcchongUMF.N19AADzRsPGi7bjTgCIXihZwrQGnGzBHeTOB2tC2UxP6IIZUip74DSk0ywLHp2JnvIby8nR854rQ1EimhQTe4eZiaGk6hKCmhPqm82W_GADKIPF5_p4jLJ2hiD8vOQMAt9u6uMGyB2RV6aPpcJ0EvETDAjt61ICKaNWfCxstNFrGqMYZCndYnJz8gxuj0uOPnJWymq6oTayX9040GZdf1ebumOOz5zvyP0u8DrpKX8.EnFYxcqMYokLpg5cNTfVwxq4hcfqn2Y7gP2LyerAVDRJOmpNFDWsUkW1Ya_uxyPxaSxRYqkEt8p3l.1OH8M8xG3DXSPxlGdayZlTfxdONlUs5HygEHmRHiXEgriUgsDlqYp8ene2dXDPI2oZWsxbflLAmhLRFbgXo2pxQtJ9Pc2HKZMjf1ffG8ZS1UFwDkPFN7bF.ICa69X8Op34hDxg5pCH5poSywDnHNMuq2bavuzGh76zO.WaplRBVnan8vhNC8jAesy0WkQokza1tWN7eMrsSFHEVbC12hpRXb7dwYqeiBZKEsIZrSBwblNwf7UOf4.UJwfXPJNAOLUp1zaC8iBnk4S_DRGPq2xRbAjMKvLahcMso0LKwlPDPJ2Gmva81pv27NK0ZRcskqRqOT9UBwRXffGHo8TF3LDIeBXjmeGqnu6W9SwRtoENbSa28yn1NSbbkg22srKvtdavc5gRlt2RdKbqOQViZHbN1PshnFkVjijVnsgX3UJzA897kVMOPxcuWzlWtSTWnE3jqc0tUYNs6_hgdl9s1bzOOT4B_moOu.458.YuslCmmcrGuYqx_PxxB2Cogf4.f1GCAb12_a0o2GQkM.4Z869t5kH6o2l0qkLeINZ4kCwsMs0EvVFzZpiMQpZLrdLJcuSL8D6u_lSMRGYMPb9iOoCYjDUaMNPULDOdD37yY6yRdoaGWaf_axycIzpyuusZHjTWT1efkvrIn85n02nzaa5DBjPgwsyz9l607DLaQkwmLvb5mhPJ2ChHnQyypTdFvARl20s.92p.q1keuiRhgX_8fqTX.hq_uS4n.r5HJGLKx60TT8E9Vc0wOea_XrgYL8fzlysPy3.N0SXL.r28WhYxW4eqQ8a1I3dtuSd1lVXaGXyE_U6d7DMyhPag9ANOTfz73NvJIPqiDvVCP8QxpLkrWdBLAYP01N1AuBG0ysm0qdxp2WhiaNfG_ES6J4MpXoH9LOPFAjuODAanJS7hxOf86t73Kb.yYRBtPaa0.npq4xwtsZ8MRzB.3pRdwMJF_tyEzABjUMkNbl6NU_2z.kdWF4nSNGdtzFxEaHPcRfjIuLk392dFhNSq6SqhSYpeuJ6cby9U6lgrLpzniuwokJLS0R1HfrCf6TKQMynCuTSXJbCMxtqye464a4rkrIJNCEZZ7iTc_fR0IW_RdUu6l3sOuzhRAyL2xT2GCkfnSyZidVPOmXXMCrD3PN5y_PuxudmlMECPBq9IX5AGzM2fOcR4hS9TycTy2Hw1lzvonDex7b6NZhYAopBiKjj25ytc_2LRDEipGyzYXGK1wooLA0e.mB6yhQKvz6U...5S_K3Yzae9P0NAvcoANXcFWsmFrGfHuKxA3yTFTbtJQvsu3xa7GjHazH3ISHtGWkkfD.uMGu300ebmmysrkmrxzYABZUi.loWd1c126JV15KLCqQhX41YySi01cEDbOgyo6cgvbWvl6QWwkPL6_M30WkgaQvKD.IvVrn0XjPPnybwK6GMRJcO49mrgonrihzPPR7w8dEucuCDRCL0QK20lIb5km40NUV0NaGdnaqB2FJu304x4KhFV.0ptxkt1b9AmIhqEV2FfSAtGAi4Ew4JrwKWxMAZ.KhXFNlBdWgk8",mdrd: "Ff2IBeHseSS6ttkrC7DMi1ZXYUHKJ3ZswlCYvhQpBH4-1732756546-1.2.1.1-AxA.ANwulHNuOFw3x9deJmLjd6XqILgz._tFED1B98TVudB6IGkBTjis_Q0NyNl2RtPeqQk2m.uVE3K5NNNNmBpQqXFSPtbYrUk9BCpE9BO6Z9S21EEsYNqxdtanrubzCwkGmDssMD14qLR_QSuqswaipXkAIvRcZxBReXYXyO6p6FFqah1q8njSb4nwTyl_25DCqFL4Yu2_WoJdoAXaE1bskjeQmYGVGTVni4Bl29pC8PiG_Eb_ngbd3luDTPR3XjSHjnuQeDsp3tiz.6boJMmUiFXk7U5EWwtQZaqAe94b.0CAhLoJN0GOExJg992t4UtyxI3nEV1xQ2rrlv7g6BCYm3Pw6VqgeMl084ui.2CgXW6x.Rq2tUVB.R5_iU4PkPIicjmT_q7now9wFw1QOniosJyCy4ErODiAIa.EmIl4IhC4qtsk_b4DmZqEOb.1TxMuMwKPWx4TbgtS3_8oe0B0iGxVbXKvMfOKMpQj.RJgRvRXjJMI79z1O3ByIGguzPBQmE2MEuUKOi3XDUZ2AoGDjDBqpi4Vk8R.ho92nHnv1fc4tj1bhEPkw246jdL.otx1Fr5SDqI1ivFQB5VggiZ5rBwOjY4Kuo5MrYdEza0hXmZkBbFZniHE9785dYiQs6PlK5EcMTX05Qi._w1Kft7eDeAOeABGVAfa7IAAZIUaxIMb7QXHx8Hd8_zxIbY1Ai4Hv.fPyjiSx06s7e92Tdm32bYMaq16K2_FkOezW3Oe4r1l0bvJ06ODlEIOSXBUfG_910q702a9fv3BmT4MwZdZtFYh6wsepqLy5EpZWCFEL6isnkk1YUWVbap5HZNzUN.GblzH.t7WvCgmcfhz4cBI6wSbVzJGFOHDVu30mvOAx5Us2eei3a5KJAx8peKlIHBxiaIInTpruYVGy3Mo9cYaOK0qsKn5vqPCK8aaHZA7wGxvaJffe8KzmBjJ1DZoDjsIXlkfG.nV98D7lVZ290ogEaZ5p2iMd.0Qb.a7J59jagqOHxZLP.6bcABRusfRdApfSxCFZRPNfSBDxkPUChaeDKG4JBtEdjxS5AMV_wsWo6m4eWBSgQZ9uD6a0_ymGwbxff20yrQW9tOpIbbuMnApmwr22mag28AHV_ayo6rye9A5kTGUXHb_qTvbuiacbNvDln1dR60FPh4riL2C5eY.5ii4MAwEVMog_gruB0EB3cFiDto7rT9qaf8TZoxcNbfz8EwpOY0arPMpqpVAQQpAXqZd2wua066fNgN02WpO6y42UZ9xl6AzHpqboqL70Ll4vjpZqJjgmgkYJhLmIXmFE3g4uHLttJ3E4VhUgYbF2s6FjVibhH2_Mbp0a8NHtoOnTa7PQ1O8NjKEthaG4hKD4ZUF4mEKbzZO3FaBgs3ogVrW.Whk82Zj7dwHdYQuf6wXbMZ87pfMKSCry.g5aZfPVr9tWCo1d6T3QZg_eBMlnAw4i7zmeWC2EEWhQui3qM_b3ll5Mt2G3Z6Tal920pHaRWSVFwE5oEbspcEl53l20B9gtEE5I2M_J5XwDbJq0GEGRf0UXUH7CLxP67bEomANKwLReqygzaeLLUFd9M_KDr21KvG00w1Il1Q2769B3bXTkT_K9oIoEjEWvZQz3OQJ.T8mxGg.MJ2OKN5rP44ghLyDY6t22F3TCwYqcEax740XjVYWOVsLxIeieANR8tw9x_DsW6sto4AUKQlkgwck1dREgffNmcsjzkRzTtbRx4jouu2re1FaidSx6b_3bLcKwAZiU9LCylbLphdE9ZAmcLMOkWebS1XAU2UCArFGO.G4xSOz2D3P5eOFS89v87P6FaZWaskk4xpEZXyYWiIILsNx81nPtnl6l49xdDDqs0HmT_Au43q.dwtLV_FUFKR5kq8goAq4CBriKKOXooFM2Uxy1fhURQbwbCS0XDeXl2N_RR7yrl.Dv5YmpqchlRkvoInzm3VylzdZaAcP2A8"};var cpo = document.createElement('script');cpo.src = '/cdn-cgi/challenge-platform/h/b/orchestrate/chl_page/v1?ray=8e968240ccae4022';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\/full\/10.1073\/pnas.1012231108?__cf_chl_rt_tk=uyEAa6ViEH.iW7UfFAbD0FmEHE9ptp_dsi76UjBtOW4-1732756546-1.0.1.1-CouA4GdVNgQLpCxK3UADCsdmfmFRQjyOlRXQXq70xlA" + window._cf_chl_opt.cOgUHash);cpo.onload = function() {history.replaceState(null, null, ogU);}}document.getElementsByTagName('head')[0].appendChild(cpo);}());</script></body></html>