CINXE.COM

Just a moment...

<!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: '8e969cd4c8d66593',cH: '4_BbqzCnAZjZsDSP25EmFxeArnC0K88sUn8tyWmD.sQ-1732757635-1.2.1.1-aNYww.O0wM7h8MWvPXHD98y2KYgCpPeTWOAVnm9X5vUZfi11b7nbKYEw.0wwKrv5',cUPMDTk: "\/doi\/full\/10.1073\/pnas.0409643102?__cf_chl_tk=az7T9Vqg9f37KKPIgX3rGBccvYmMwq5icFXnvpD76qM-1732757635-1.0.1.1-w.poNma1bNud5O1KG2C8lrVZmonv43Hzc4vH9syHEnY",cFPWv: 'b',cITimeS: '1732757635',cTTimeMs: '1000',cMTimeMs: '390000',cTplC: 0,cTplV: 5,cTplB: 'cf',cK: "",fa: "\/doi\/full\/10.1073\/pnas.0409643102?__cf_chl_f_tk=az7T9Vqg9f37KKPIgX3rGBccvYmMwq5icFXnvpD76qM-1732757635-1.0.1.1-w.poNma1bNud5O1KG2C8lrVZmonv43Hzc4vH9syHEnY",md: "EEeEoHgTC4NhHW1t1ps1pgTrJXMjl7STizQKBOTIj.Y-1732757635-1.2.1.1-V2acUlQ2xvGaZpx1FEpk38LLUzwNEroB88XzskY55LT_ByWxnNbVDsOcQJ8EooS6UIS1b4Svkiu0sf1xccptSYXZj5NVJVl4bC6E1ldDN3C4DsktsR2f.OPlxBsU_jt_Zm04oHQTzk.UYb1JXJ4ttN52oDNbLBWkV1D.88gzA78EfhMjg_EEOckkTQfYM4Ab4PdX0rsB8tkLQh3386Ua4Kd9ovZPp8sVEv.aWz3P1Y_NfwPOoAgQtt1ThoK0b4d9H8mrAdRvKwfBxTxk_VmAB7yDEkCYsoPA63iyAR08pA8._PiwPIF.kYU5ugDKuk7Ffby_ohucUZhsTnfpoCOSuJyEvyE7lCIRIGjAhShA0y8.uauCf.HmgxMtahf3vddfNowWJ0lEUYuw9g7XYUctaoJ.83e.aof3gbPYGfy4YKoUdY7esacKCkbP0TNpCiu.SrPb8Pb2eB7Cg07AOoQjVCnnWzuW.n6kZCe8RiECOBAiU0z7Zha9BydIa_zrjMRXEQYU5RRwzL.Hjt48qFj2B3hWsLjqsuwNEXGmREK_n99RKAbvks4Yh0sAaLnA5pbGjICKm2kN_dev1anwZiPMeWZYc4um67mIZ9DCEffY3C5JbdYXEV1KzfRUyxwqrCbLo3ul1F3CcJKAHzGYsBd1VVQ2lJjGuIB5OybdakOwgPQ9W3hAKeEK4XesSGab6ys2lJerBKpHZK3pgpuMCDDJBFhE2W7euXzjMO6ZPc3Rjsce94.hYae4tPScvlytPc33rCjYC2fCa7Z1xER2fFpgk9jsG5TAYmwxVW6vskBq_ex4xcYQ2EXCtQ2ae7csaJfjTwU.HM4yDA2YEelXKD9MDdwUKJ.rhB.q1lBRUutjnAkT7U0ZB6Zl7KJa01dBHyDhLpmN3_0nHH7nufPrf4fC56oSjzxOvHAzohG4ktyHeh5d9F1e5KhL0ipObyu0uOl7eYNZ75vFrIHDgU3Vf6holxdL8firmh_mkOSPmo67OD8gFQZPjMlFMgu4yzmXbX_WzKJSeo90OFtGjoV5Mgx88C_ZsM8YPwvmDX7s_dWXvqBDT4Gym3jLpWbxe89p.1uW5tKmCFdg9rg8wlqI.KRbE9A6bf.KREDiRM3V4e5puRahAnc4cxmmwGTTE.QlkShpyX3_UFU26FJd1.O9iL1e81RCgzcRvQYjoSDYFPHs1OmkHzkojai86jvPuJUY0oPbivDs9MO3OwBqXEgmxEAkJ5H5d_eP2B8lA94WIxCGWgWWepK8vjrW6dVNTq2G3vnnxnrdrzwvsCIJzNXLwYSB30T4c4ODWX5W9LCo55MDl7h.jvC9vRC2GxqkN16M0OguURDbyKAvRgS3_H4kTcZL.N4yYpCUMc8zdxLKtjMXwgxwz94YVuHDJTNKK4lCMKq249p7Mjd35M0Qsz.hOVlFVT88giiv3MKODDw9vJSrNB4PvRJUsuf1HDcbQr0E0e4Yxq3mN0_ZSDBo7A8IpjI0d92XWR0UYkeVokqJ0k5fl8Rry5ifViq4ebdKR7P_PxQ0f_PdJuZnmJ_a1C6Fven7_n1nlxWkarlRYz8JwwwhiY71iC5dyEBZjkbDj3kuphvPy2C6AtL_dmNBYOqyigrHR7RI08dSGkc7HE67nmZ_jG2PSDUizoUv5ToqELA9jvV3531nKFsQLqAOBinn3Ncpyk_qkd_35paeHLk9p6EXiIB2IFBAKYKNoIJrs7OdXcmFF54fGgZjfQyvqzyd9nEjR5G6c.4ySydTHPAf2ZbKYUS9RWkRnhv8GbrJbxTLErkjtZqL9sxC0Q0VjUo3PpDx1jueQwSZX6BB7XHg8yCdvMCuyEmgVi271OxdX3pGkdLpHcouA2PCqqegZ_sY8hcIYTsq37B8xBeeIsqIEHGc.VVKoo9gOU8OtnTc4tkH18Q3SFt2s1PhAvKa8tb..w2WUSNpqyFHgdgnHuuZ2CrvJQbJtfvt3E31r0HH1stdXQo_wDpeogtVE.Gn5w0K7rAT_OU81TLtb30ag0HBE24E7ZYQNkma521hhluxVDLFbHAhOBYccotehUZWNQ.ctYSxYDzOOOwIjoRQE.aeNNwAMETfCTh74.sayT7ZOKHaSv_QqAC1bC7iPf4siq7wOs4ecrtNYmA.r9dH8wM.j3YXW4gwxIXArnhipo.47VXZSNqnv5QHjC4aXYYUHH0DAFY.GRHQVoJyKy5NFylTAeMluK1SSYkQlbRc3PDwrSoSMtwTCY0bovq9HxgOzG5apKUZqctsJVe7vuOSG2CA0CabbGK7YvnqO53k4j.n4iO689ujbXYvM9ds4rnUc4Bhd91wyq9fxO4lr_zddizPnpFWcp.DwsFw4iDed1oRx9zJs_S3VubrldTTi0qbbzTVhy0l7NPoKnZN1INwKPLDmwVwZKW4fZTxwc2rslTEY33MskPfH6xJ2WitzyMfNobRX3UIpqT9gB51QnX2x3hB3kzGkB5vMLkyHve9LuItD_tWcQBpwLL5qqdDJ9qJy8AAPb4gcwSsc_g26oyQVgjkdiJ99f3XJM6_AU5ZGUz3sijPSey5diYkh1HUDjVYxD2JrW2aRn0rYl16AywWUadjfnGnVO0RRWmuVOkqGSY2RBNJ02S8fbovIvyFEbJS_RR.TxjFGNncnWrztTz0dG6orCQY9pHnERyI3TaBr7w45LU3lWf3B3Caw7vagQfbUz63_CGrpmqL7nrptNF4kYTHuofLkbOI3HolKLYHMXKR2tC27P0uA2vtRT1aFFIUvOW145ccoydRY0vkaXiZlY7UdFo1Qzu5bMXuNps7qzeH_K39HrVxEHGVyYFLHPsaS2y65Ezqlw7DloCea3yb3lmmpsgXkB3F7QYvHGzCgyJh3Y8ITTnWmgJ1VoQ6ZlTcpdGyfU0b7r7Opy5p4RHUKYgVs5ND1UmqAAw3h0x27t5tqS53l0Uqz7o6hYyfyLo4znyf2_PBkGb25jYiU9ATsI7xALiEf18",mdrd: "XzgmHhFWsBUWZKOQnZWzmIIBTV_c51Af4wDOmalNPKY-1732757635-1.2.1.1-zd0Cf0KHl4bvTzwOHOq6lajx4l4wHg1gcl4e0b3eXJwC68DfbxwIjVzUHCHC15UOBkHg1qjlEZCM3bV8yATMzxSTgx8YeL6s2Iv5s2xUvCbFRkHNwAdtz2JIex.5TT4hZ49hhfcl8YPCnFfVtHSMa.JgBFl1dNAhyw3Nz09lr2O.0J9d4RWACayrCgH.omroITlzxOEilZnyMqMKbfRxjoRIFTU86V6TYryv7e0zd8kaosQMFVo0B4SuCKGFiSHRxsY9.xtfRF9CkHfxooMSgzWAKA7QOT9Da.K_r7i9yRkdZqv2zvnDUgW_c.gSIFTPczB3wBUdctYDtajTGqwZv7A3uk44i7L6WGWqA5nOblhT8ZjLiYW4FBE2fsOSrhg1LqbLuYHyIJk9_5VStQ6MmtEfxJEMFVnDvpnSo1A2eijXhcWWWNnWluj1ZmF7mV1T8kgjTFP1E7F3n66GkepeQPLXaljecoLM9mINJ.eFjRCqFqQUUwTc_XvXbgI8uMOyN6yqAC_SHoAxA1iOcJphO8N7MlVqpwv.qBZq9t8zKxe_WnBbxT7RqSJblrdPNlBET0Z1cgaHq56tkVeF9WekgupG02tRy6p8VPn.L75kVp26Fxs0Ezecob7wFOb0PStVOY_ikx5XWgAnlkJpgd_iBVmu0bFTLApZmJb4yYJ2U2IKoWtu.MEV1_sEXILj.0plh9izU0oU3pMJ4rnJgQYi3RX3GFGvhCDG8IYMjPkKHC6ncipg2iQUNWL0jisyJkyyp4XYu8aM3PONzVyICWchUXLKPNILmIQKbCSHELgfsmtNfZc90O7i4obeqvkzvuAEw7Ia93NgIBuXy9.Cj_K6.WqT1dbY5.RPZgzVpS04D8yikvMGSw59N9lGiwE3ZOg5VOTappJCIK1cB2MRvb7F3yV7WMmSsu2UNMrjWMWc7HxJZfeWS7xji4dN2B.xXgqgBiA5gVCWI.zWK0TFtsFet_Vqk5i2tVPpRjmRBC5PsI5skBBoFQxshWYKTT0Ja_aVi_Dtft0raIQJZRbZgraBvwufIQIW0q.be5jaXqJRG895YmWdYTqzWsRfgRNfjFNX3a_dVEAHAiteqZrIFGxgcqelCMlMKS.CjB3j00TOY_CBKYLlnD_fB9k0JatweK7p6bO.noIFOdxn8UzVYAk9stqsZosgHsKevEOksuwFRDZ2i604RRraRMtYg5P5ABM8HZGZsNy8qrePtCOOYK34LWp_UvfABZvRBNAGr226aj6MnqivsZHbAYegCu.yBjsIs2839pBsbXqwjkzF0w8JcpmiSkwLujjJkYfJpU3EPY7RnJYLCK2xXvXSugkqBux.iRvuQdDdzJ7qY4Bo5kkzWeHpSGzPFSYjHYQU2glyzptAhLiaIjbZl7Hl3AiTr7z5_WvxDGt9q9OtgvG4CXSDA8limMVyzvnnwokfVFeFAswdfaRV39Jcv9PQfCWeiNTgtOA9lMKnpqgIGYCTUbsapRpYA5pb1qvcQAAf1qfjqsrhFs645BBGVVDXWqI0r0oa_tm5R3NdKlh7U77m7hoyJ9a_h3SjcK_opY4Bmtj2NKPIsGk_QEcvMH1pPq6BhydHWsTpCP2yghQ_W8hyTshz.O3LYHqQUV50iOvz5QkF_jKfIK0wV3kI0n40nBOW4UrWRGrvCl7HpEKL16cmvx6zUxwbVj2lIGiZ8g81.nuEQPoxAWsbbstD1hzdbQEDa.1tulAtHWR6BCGAJ1EzJTsYXYdd2m8mrz5CpwIvNPwbnRrT1hXpNkLi3WvOwT7K2iKRWR2zFT_mN0rrPtFRXi5fPBG1S3PR4SujejlQXyGs6yxlQsCIW4GeeZK0EEEmBNIMvd3G6IgJ1hg4Tocr9W1uW04R8SMLM.ez3O.2SUVPBgxQ8Hs8shIJeBWEEeZMH_Jp_GD0ahbGRtQLnIFf3hizU2epVmrzLEEPUPR9OAn14qQ"};var cpo = document.createElement('script');cpo.src = '/cdn-cgi/challenge-platform/h/b/orchestrate/chl_page/v1?ray=8e969cd4c8d66593';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.0409643102?__cf_chl_rt_tk=az7T9Vqg9f37KKPIgX3rGBccvYmMwq5icFXnvpD76qM-1732757635-1.0.1.1-w.poNma1bNud5O1KG2C8lrVZmonv43Hzc4vH9syHEnY" + window._cf_chl_opt.cOgUHash);cpo.onload = function() {history.replaceState(null, null, ogU);}}document.getElementsByTagName('head')[0].appendChild(cpo);}());</script></body></html>