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: '92661de5280ea091',cH: 'Jhd0qOYpX2Z0p1By3c9y5D2K6IhHabm8aGHEgC7C_FE-1742986537-1.2.1.1-aq6UTlvZb6T2RS2hoR3ueM.z6uV0U4hkW1YqcikKSYkl47DgBForTvABtvBsHYwd',cUPMDTk: "\/doi\/full\/10.1073\/pnas.0804397105?__cf_chl_tk=gG8ILjY9c0b_PFIFrKl6R0CbbUprsarN2wkTj3IuKWs-1742986537-1.0.1.1-RuEA96BPvsrFb0W767xLQ9mvwzzTYCyAcHwhopGx9_I",cFPWv: 'b',cITimeS: '1742986537',cTTimeMs: '1000',cMTimeMs: '390000',cTplC: 0,cTplV: 5,cTplB: 'cf',cK: "",fa: "\/doi\/full\/10.1073\/pnas.0804397105?__cf_chl_f_tk=gG8ILjY9c0b_PFIFrKl6R0CbbUprsarN2wkTj3IuKWs-1742986537-1.0.1.1-RuEA96BPvsrFb0W767xLQ9mvwzzTYCyAcHwhopGx9_I",md: "l6T6F.lzFdBws.Pk.dUj_sXqrji9LLM_MnhYMAjHvtE-1742986537-1.2.1.1-zQbCuju4DTtPTe5XdRdw8YV21W3pKt7NQBC9i5sxI_LIKCJVYHf7hpNMZr.kBVYBho3qar0l3oMHCv7dKyfno5Zrwnj72uzWvxZ28LAu_j2vrgra3CMakd6gBuCUSzMpmStmNuyjvHa87NobzDKCBrLQmWsAUddch1o8uWwlMS8EltQtSb88jVQQGvhjzx3bqzR4re0YN3nNdDYG3ozE_B4UKx2MJ2Oz7N7rZi1sm_IHJ78zcYvFFmQqBmVxyVYaHaJgR8ulsBXS.m4.1tPxQmZMTxlf_fPGaMe3HaR6Lsn21zBA.5UrQGVdnoz3DJkNEdk7tCWFwIypyapliY.LeIypAzfeuHVaSLTM6HiwukEv5M4aDxRNz_G11UYFcMobMiF23wvJuO7d2FpR9JBxCE5VyKgJvUXTJV3Wb2tBTclQYmNC7WUrTfW.AlkCGFxEmTM8cW0OoX92kDzWf5JImIC8GiLKcThyZ8TeElTMun6vITN6fSswg6lXDq2lT1_QLm3FmEdLvvbL53L4qliAD_UxRIny2iQNGsqAodJIw5gwGrOvVrBziZ.Ahi9YlcWn.2.SSSQ6wJcRIKGXJ3cqL_QIZUIflMN6eUtYilIloPmd5_9oVoiBcyYRNsBNl2dsqhb9gZ9DUfJ6DX5i8OjDAlo.40M1TxQrpIX.JZVVPjxE8cr62zcSUTcnrrD0jBcUcwgoRgi3iig3CBiesYD1KiU8A9S.IOvBQkRQArla1olpPp7.adxpKBZVfpNI2qA2..WR6gHyN6y8nSFxg89.WveRWpdXeyFFyO432usVjjhOP9HbTaQ3NnbjdPGw7rHcQwx2gO4O.0LQoq2pNwM_7vNEEwiR.sPA3_pJ9WySEyC98WNX.z8h.i3ZbsMpfvgHOfQMPTsp3K4T137IDvPNAmY9POe.U0OAfPIxIa4qBZBGOTrAEQfrNIlqTcjQlMG0ef6.ERnnxP3j9jBeSJTimP5_L_ONz4fFSDjc2I_GEY5IKBXteiS67Z025i.sNbgAJ90GHdPQnIjXVgXRPJEVjOg_fyNIfGpTuabM9BJ1XxUD3lhT_REYgJlAMXFcudbYll514liC.kWiCzSrhKlCNPCLDADIA3UjkNf2uNSbJswhjFCA6dVmN56qUwYIfXREzUXnl2ski7jHXgorUG5AufbZrjwrSubRsN4Oo9oG7E1Di_lV52Ft0aBYpgnjvLPyAw1Yhe2NfQDfAYzKE8STHNykaMEF3EOtynWgMLnSqOzVT190psce5JE.2G8bE4wDqoiqxDRk8PWGGfWKBOE__Q",mdrd: "VO1_socNHHff_zw9QKhUi49sBnEqrXCaStT9pFzlXd0-1742986537-1.2.1.1-dIMmR6NsJXuk1xf2bsZfXMVf_qF5JcPhYxx9A038tH.uzBrsGS3BFHA29aj1f2Q52mB2xPZVNT4GU5fLfzFI3dNokEaTnvt058XXvkfgXF6nba82b2rN2uiVYiJYAon1ZAwk6CiVTPxUP5lSypJMi9PfrOELbIzCOcIs2dP.BZsluNbDgkReSP.n62i.M4LrXjz0u3eVxLfOSM6H02xYtqTdMzQMT9BqeiiSLeolHiYvOs8XNH23YKNFl84fxzRIEoP.xjf6ba3DSAFemcdBQxDUNWusxmEDysYqaoCAzEeT_KzSG7hSnwVj8X6dCsyHTn.TqKZbw7AGRv1KyWp2YziYCbDvveHagRI9pELMuGgFxSB8blf2iecar143YnzWphTkl3vu7StVOAM7mRb0nHdcFi4NVTMUiZd_VJH8hKIbcij4SMYPR8d12hw.FGJU8hpZzdJC_Bc5Bfgf4yZEfyCl3tAXR.DxpxKeuqequVPWLrVfpQgFHEe26cgjNcKYIc4oZCmByElZaVlMhhCj_.zYE3ag.ItlQf5pQn_5MmL7pIXj4E6kUMiAX4qBdnCicR7NPMDqA5QMQr5SOrVFMg_GMh_TF8a1Wb7yn648.Qd7TB73p2Ab01riHr3DygRzijr0Z1vjergUan9HSylbFCGGK5WxElt4zFm0ACRi_CoPu.bMGzxYshgCLe2EMTlRxck28eDTx43vqQvRpVpGEg8dpJYu80NQ57Y482ESv6utfh0qXXh9xfliGFB8UVxdKiAStxj9prqV.1vI3hJVJZWV_Iy6Xnj9H_2QdPxK5G6iVGnLxE4qfCGMsU9P6fvz1_PnAOflBrixyUsBHhkfKtKIkWmFicVHbARCnpFeVV0V2VhRarF.BtSfvjT5vvoOqrBoT1myB0YNPj75S0OQUBZdSSyVZ2xouPwreqAGkI_nhKMNIIrdWjwhajT_NDvIZzo4F3JQbTnX5GfN9XHF4aDq0BVyi.8Jj9_okF4e3n0LKGK8BFcVyWSIkhu.CdmZAuF5fgCX2Ipr4fCyrW3PHUEJ9NBgMEWK38aUYfcxS8PpzL9Qtol8UOVjl5zX5YZOSWS5L6R.ydNHkTJFPrYj_od5c2JZhb.3MHGuC25MbF45Z_GQWdaIhe0nmKjkXCAXWPETGatC5AggWTVX5Y3ys7nGu0zSDZWB7yu5Pid0VN_y3V.GDFqYwolPzP2os1rj1qMEs6Hz1BzfhD6UEHdv.6ZvXMZJKPYis3OnCn7CypBl9DTYb7uqSk_T1dplsbObMFU.CcGI8Z6fAtu9cLJwXE2p2CVYbsBrPLqh5MsoJaj8EHLEG3DtO5BvUbB7Pt3XyTieCXSYNxCurwyQG_EImMetZWE3SVprfqp1Xv5UbpDJIG1KYXG8ihZrLVCsEEIT51sHLIHRQYJX7YwtaPOkLnJXBhmXqP32zkAF_lXE3UulVVMC5Z_Nnq1.akRzAfpPsaezUfxxzMowznuQwONLMCWOPNl4noCe_gOi82DK6VHJUbSR_hb5a_FeFSpNFEeqBb1vOYsu3pKZlVkdQMIkuUivLalsFuey3AIrIbiOaVbzU0qTPMvJOupKUYrLZm7p0_igKE5OU8VfFl8M27QVB.9AwCk6fqlCI.8FWYjgqGI3tTrMGTHAQxoSv2MIRtYXQvDJPopapGmu2q0TSQVOmGHuoaDkc08HPBMP5gJHLLuIAz5aZDIa8FLU3QYpubLHmQiHcZwxaQ4xHuFcPNBmFgCjhU2xovUyF8.FFe0xUNtH5MI_WLNXSPEmDApqhFyUk0lQZb7BCZi6oa4RqHIjSTFyni1WIpnZb.ceGRL_YRNfxKIzwM4pjE3kBiZM7xNcJ1pzto1wBZ5ImbzpCPW.5kgv3FboaS.1Z9Q_WI8p0JETAuYqB7EU4CcT9wHb.TDCFaOvlyjFjOqorbujDIR55H8PlIHlvtHjfMxVVYIdoAyF_MxAKwjoH4tjd6.1Apn78aArlVENkprUkVaEa9zUJ8IAGUbuiT9kmdh87yTizehavwyZXZ206vneCAksjkCy"};var cpo = document.createElement('script');cpo.src = '/cdn-cgi/challenge-platform/h/b/orchestrate/chl_page/v1?ray=92661de5280ea091';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.0804397105?__cf_chl_rt_tk=gG8ILjY9c0b_PFIFrKl6R0CbbUprsarN2wkTj3IuKWs-1742986537-1.0.1.1-RuEA96BPvsrFb0W767xLQ9mvwzzTYCyAcHwhopGx9_I" + window._cf_chl_opt.cOgUHash);cpo.onload = function() {history.replaceState(null, null, ogU);}}document.getElementsByTagName('head')[0].appendChild(cpo);}());</script></body></html>