




<!DOCTYPE html>






    










<html lang="en"
      
        
      
      
        

        

        
        
            
        
        
        
        
        

      class="pb-page"
         data-request-id="9e82adca2a003ea1-ARN"  

>

    
        <head data-pb-dropzone="head">
            

<meta charset="UTF-8">






    
        
            
        
    
        
            
        
    
        
            
        
    
        
    
        
    
        
            
                
                
<title>PNAS</title>





                
            
        
    







    
        
            
        
    
        
            
                
                



    
        
    

                
            
        
    
        
            
        
    
        
    
        
    
        
            
        
    










    









    

    
    

    
    
    
    

    
    
        
            <link rel="icon" href="/products/pnas/releasedAssets/images/favicon/favicon-f7229df5ea4aa1e206bbb00228dc8de4.ico" type="image/x-icon"/>
        
        
        
        
        
        
    

    
    
            <link rel="stylesheet" href="/products/pnas/releasedAssets/css/build-c9a2aa061a6ade4dbad3.css" media="all" id="build-style-sheet">
        <link rel="stylesheet" href="/products/pnas/releasedAssets/css/print-c9a2aa061a6ade4dbad3.css"media="print">
    
        <script nonce="9e82adca2a003ea1-ARN">
        try {
            document.documentElement.classList.add('js');
        } catch (e) {
        }
    </script>
     
    





















    
        
            
                
                
                
                    
                    


    

<script nonce="9e82adca2a003ea1-ARN">
    window.addEventListener('load', () => {
        PNASdataLayer ={"ecommerce":{},"page":{"pageInfo":{"pageTitle":"PNAS","pageURL":"https://www.pnas.org/action/cookieAbsent"},"attributes":{}},"user":{}};
        if (PNASdataLayer) {
            var ua = navigator.userAgent;
            var deviceType = "desktop";
            var width = window.innerHeight || document.documentElement.clientHeight || document.body.clientHeight;
            var hight = window.innerWidth || document.documentElement.clientWidth || document.body.clientWidth;
            if (/(tablet|ipad|playbook|silk)|(android(?!.*mobi))/i.test(ua)) deviceType = "etc";
            if (/Mobile|iP(hone|od)|Android|BlackBerry|IEMobile|Kindle|Silk-Accelerated|(hpw|web)OS|Opera M(obi|ini)/.test(ua)) deviceType = "mobile";
            PNASdataLayer.site = {};
            PNASdataLayer.site.userAgent = ua;
            PNASdataLayer.site.device = deviceType;
            PNASdataLayer.site.viewport = width + "x" + hight;
        }

        window.dataLayer = window.dataLayer || []
        window.dataLayer.push({
            'event': 'get-meta-data',
            'pnasDataLayer': PNASdataLayer
        })
    });
</script>



                    
                
            
        
    
        
            
                
                
                
                
                
            
        
    
        
            
                
                
                
                    
                    <meta name="robots" content="noarchive,noindex,nofollow"/>




































    <meta property="og:title" content="PNAS"/>
    <meta property="og:type" content="Website">
    <meta property="og:url" content="https://www.pnas.org/action/cookieAbsent">
    <meta property="og:image" content="http://www.pnas.org/pb-assets/images/Logos/header-logo/logo.svg"/>
    <meta property="og:site_name" content="PNAS"/>
    <meta property="og:description" content="Proceedings of the National Academy of Sciences (PNAS), a peer reviewed journal of the National Academy of Sciences (NAS) - an authoritative source of high-impact, original research that broadly spans the biological, physical, and social sciences."/>



<meta name="viewport" content="width=device-width,initial-scale=1"><meta name="event_group_key" content="b638b1cf-1e99-4e58-852f-12d5fa75f1b0"/>
<meta name="citation_pdf_url" content="">

<meta name="citation_doi" content="">



    












                    
                
            
        
    
        
    
        
    
        
            
                
                
                
                
                
            
        
    




<meta http-equiv="X-UA-Compatible" content="IE=edge">
<script type="text/javascript" nonce="9e82adca2a003ea1-ARN">var addthis_config={data_track_clickback:false}</script>
<link rel="stylesheet"
	    type="text/css"
	    href="/pb-assets/styles/pnas-styles-1766506067190.css">
	<script defer
			src="https://static.cloudflareinsights.com/beacon.min.js/v652eace1692a40cfa3763df669d7439c1639079717194"
			integrity="sha512-Gi7xpJR8tSkrpF7aordPZQlW2DLtzUlZcumS8dMQjwDHEnw9I7ZLyiOj/6tZStRBGtGgN6ceN6cMH8z7etPGlw=="
			data-cf-beacon='{"rayId":"6e65fb942de2942c","token":"4fddf4ff2db74c469c27e6f3ddde2174","version":"2021.12.0","si":100}'
			crossorigin="anonymous"/ nonce="9e82adca2a003ea1-ARN">
	<script defer
			src="https://static.cloudflareinsights.com/beacon.min.js/v652eace1692a40cfa3763df669d7439c1639079717194"
			integrity="sha512-Gi7xpJR8tSkrpF7aordPZQlW2DLtzUlZcumS8dMQjwDHEnw9I7ZLyiOj/6tZStRBGtGgN6ceN6cMH8z7etPGlw=="
			data-cf-beacon='{"rayId":"6e9db4c0dd526450","token":"4fddf4ff2db74c469c27e6f3ddde2174","version":"2021.12.0","si":100}'
			crossorigin="anonymous"/ nonce="9e82adca2a003ea1-ARN">
	<script defer
			src="https://static.cloudflareinsights.com/beacon.min.js/v52afc6f149f6479b8c77fa569edb01181681764108816"
			integrity="sha512-jGCTpDpBAYDGNYR5ztKt4BQPGef1P0giN6ZGVUi835kFF88FOmmn8jBQWNgrNd8g/Yu421NdgWhwQoaOPFflDw=="
			data-cf-beacon='{"rayId":"7d014c01ed4196e9","token":"4fddf4ff2db74c469c27e6f3ddde2174","version":"2023.4.0","si":100}'
			crossorigin="anonymous"/ nonce="9e82adca2a003ea1-ARN">
<script defer src="https://static.cloudflareinsights.com/beacon.min.js/vcd15cbe7772f49c399c6a5babf22c1241717689176015" integrity="sha512-ZpsOmlRQV6y907TI0dKBHq9Md29nnaEIPlkf84rnaERnq6zvWvPUqr2ft8M1aS28oN72PdrCzSjY4U6VaAw1EQ==" data-cf-beacon='{"rayId":"8c52882288c0fa66","serverTiming":{"name":{"cfExtPri":true,"cfL4":true}},"version":"2024.8.0","token":"d1e81366f89b4aa09fd7ff47c1e123f8"}' crossorigin="anonymous" nonce="9e82adca2a003ea1-ARN"></script>
<link rel="canonical" href="https://www.pnas.org/action/cookieAbsent">
        




<!-- Google Tag Manager -->
    <script nonce="9e82adca2a003ea1-ARN">
    var dataLayer = dataLayer ||[];
</script>

<script nonce="9e82adca2a003ea1-ARN">(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;var n=d.querySelector('[nonce]');n&&j.setAttribute('nonce',n.nonce||n.getAttribute('nonce'));f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-KCV32QR');</script>
    <!-- Google Tag Manager (noscript) -->
    <noscript><iframe src="https://www.googletagmanager.com/ns.html?id=GTM-KCV32QR" height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript>
    <!-- End Google Tag Manager (noscript) -->
<!-- End Google Tag Manager -->

<meta name="pbContext" content=";wgroup:string:Publication Websites;page:string:Cookie Absent;website:website:pnas-site">
        </head>
    

    



    
        
        
        
            <body
                    class="pb-ui website-pnas-site">
            






    
    
        


    
    






        <div id="pb-page-content" data-ng-non-bindable>
                
            <div data-pb-dropzone="main" data-pb-dropzone-name="Main">
                
                    
                        



        
        <div>



        
        <header class="main-header headerParentClass-e184595"><nav id="mainNavbar" aria-label="main navigation" class="main-navbar navbar bg-white navbar-light navbar-expand-xl text-uppercase"><div class="container-fluid"><div class="navbar-in">









    
    
        <div data-widget-def="UX3HTMLWidget" data-widget-id="729a0980-ae74-4b8b-8362-07d931f05f0e" class="navbar-in">
        



        
        <a href="/" class="navbar-brand navbar__logo--default">
<img src="/pb-assets/images/Logos/header-logo/logo-1624644560537.svg" title="PNAS logo" alt="PNAS Logo">
</a>
<a href="/" class="navbar-brand navbar__logo--light">
<img src="/pb-assets/images/Logos/header-logo/logo-light-1641218818190.svg" title="PNAS logo" alt="PNAS Logo">
</a>

        </div>
    

<div class="navbar-toggler__container">



        
        <a href="#" aria-expanded="false" aria-label="Expand search field" aria-controls="quick-search-form-0" data-expand-label="Expand search field" data-collapse-label="Collapse search field" data-target=".header-quick-search" data-toggle="collapse" class="btn quick-search__trigger"><svg xmlns="http://www.w3.org/2000/svg" width="45" height="45" viewBox="0 -8 32 50" class="quick-search-icon-animated"><path d="M17.71,17.91a6.25,6.25,0,1,1,1.89-4.48,6.23,6.23,0,0,1-1.89,4.48" class="cls cls-1"></path><line x1="25.07" y1="25.15" x2="8.2" y2="8.29" class="cls cls-2"></line><line x1="8.2" y1="25.15" x2="25.07" y2="8.29" class="cls cls-3"></line></svg></a>
<button type="button" data-slider="side-menu" data-action="toggle" aria-controls="#slider-side-menu" aria-expanded="false" aria-label="Toggle navigation" class="navbar-toggler"><span class="navbar-toggler__box"><span class="navbar-toggler__inner"></span></span></button></div></div>



        
        <div id="main-menu" class="main-menu collapse navbar-collapse collapse-lock-screen"><div class="main-menu__nav flex-grow-1 d-flex justify-content-center"><ul class="navbar-nav"><li class="nav-item px-3"><div class="dropdown"><a id="menu-item-0" href="#" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false" class="nav-link dropdown-toggle">ARTICLES</a><div aria-labelledby="menu-item-0" class="dropdown-menu"><a href="/toc/pnas/current" class="dropdown-item">Current Issue</a><a href="/latest" class="dropdown-item">Latest Articles</a><a href="/about/special-features" class="dropdown-item">Special Features</a><a href="/loi/pnas" class="dropdown-item">List of Issues</a><a href="https://academic.oup.com/pnasnexus" class="dropdown-item dropdown-item--external"><i>PNAS Nexus</i></a></div></div></li><li class="nav-item px-3"><a id="menu-item-1" href="/front-matter" tabindex="" class="nav-link">Front Matter</a></li><li class="nav-item px-3"><div class="dropdown"><a id="menu-item-2" href="#" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false" class="nav-link dropdown-toggle">AUTHORS</a><div aria-labelledby="menu-item-2" class="dropdown-menu"><a href="/author-center" class="dropdown-item">Information for Authors</a><a href="/author-center/editorial-and-journal-policies" class="dropdown-item">Editorial and Journal Policies</a><a href="/author-center/submitting-your-manuscript" class="dropdown-item">Submission Procedures</a><a href="/author-center/publication-charges" class="dropdown-item">Publication Charges</a></div></div></li><li class="nav-item px-3"><div class="topicsButton">



        
        <button data-target=".topics-container" data-toggle="collapse" class="btn btn-outline-primary btn-topics">Topics
    <i aria-hidden="true" class="icon-plus"></i>
    <i aria-hidden="true" class="icon-close"></i>
</button>
<div id="topics" data-parent=".headerParentClass-e184595" class="topics-container collapse">









    
    
        <div data-widget-def="UX3Tabs" data-widget-id="e657c77c-421c-46e0-b0a0-d72b63228a8b" class="topics-tab text-capitalize">
        



        
        <ul role="tablist" class="nav nav-tabs"><li role="presentation" class="nav-item"><a id="nav-e657c77c-421c-46e0-b0a0-d72b63228a8b-physical-sciences-tab" data-toggle="tab" href="#nav-e657c77c-421c-46e0-b0a0-d72b63228a8b-physical-sciences-pane" role="tab" aria-controls="nav-e657c77c-421c-46e0-b0a0-d72b63228a8b-physical-sciences-pane" aria-selected="true" class="nav-link  active"><span>Physical Sciences</span></a></li><li role="presentation" class="nav-item"><a id="nav-e657c77c-421c-46e0-b0a0-d72b63228a8b-social-sciences-tab" data-toggle="tab" href="#nav-e657c77c-421c-46e0-b0a0-d72b63228a8b-social-sciences-pane" role="tab" aria-controls="nav-e657c77c-421c-46e0-b0a0-d72b63228a8b-social-sciences-pane" aria-selected="false" class="nav-link"><span>Social Sciences</span></a></li><li role="presentation" class="nav-item"><a id="nav-e657c77c-421c-46e0-b0a0-d72b63228a8b-biological-sciences-tab" data-toggle="tab" href="#nav-e657c77c-421c-46e0-b0a0-d72b63228a8b-biological-sciences-pane" role="tab" aria-controls="nav-e657c77c-421c-46e0-b0a0-d72b63228a8b-biological-sciences-pane" aria-selected="false" class="nav-link"><span>Biological Sciences</span></a></li></ul><div class="tab-content"><div id="nav-e657c77c-421c-46e0-b0a0-d72b63228a8b-physical-sciences-pane" aria-labelledby="nav-e657c77c-421c-46e0-b0a0-d72b63228a8b-physical-sciences-tab" role="tabpanel" class="tab-pane fade show active">



        
        <div class="topics-tab__topic">
<div class="topics-tab__topic__portal">
<h4 class="topic__heading">Featured Topics</h4>
<ul class="rli topic__items topic__section">
<li class="topic__item"><a href="/topic/phys">Physics</a></li>
<li class="topic__item"><a href="/topic/chem">Chemistry</a></li>
<li class="topic__item"><a href="/sustainability-science">Sustainability Science</a></li>
<li class="topic__item"><a href="/sustainable-development-goals" class="sdg-topic">Sustainable Development Goals</a></li>
</ul>
</div>
<div class="topics-tab__topic__article">
<h4 class="topic__heading">Articles By Topic</h4>
<div class="d-flex">
<ul class="rlist topic__items topic__section">
<li class="topic__item"><a href="/topic/app-math">Applied Mathematics</a></li>
<li class="topic__item"><a href="/topic/app-phys">Applied Physical Sciences</a></li>
<li class="topic__item"><a href="/topic/astro">Astronomy</a></li>
<li class="topic__item"><a href="/biophysics-and-computational-biology">Biophysics and Computational Biology</a></li>
<li class="topic__item"><a href="/topic/comp-sci">Computer Sciences</a></li>
</ul>
<ul class="rlist topic__items topic__section">
<li class="topic__item"><a href="/topic/earth-sci">Earth, Atmospheric, and Planetary Sciences</a></li>
<li class="topic__item"><a href="/topic/eng">Engineering</a></li>
<li class="topic__item"><a href="/environmental-sciences">Environmental Sciences</a></li>
<li class="topic__item"><a href="/topic/math">Mathematics</a></li>
<li class="topic__item"><a href="/topic/stat">Statistics</a></li>
</ul>
</div>
</div>
</div>
</div><div id="nav-e657c77c-421c-46e0-b0a0-d72b63228a8b-social-sciences-pane" aria-labelledby="nav-e657c77c-421c-46e0-b0a0-d72b63228a8b-social-sciences-tab" role="tabpanel" class="tab-pane fade">



        
        <div class="topics-tab__topic">
<div class="topics-tab__topic__portal">
<h4 class="topic__heading">Featured Topics</h4>
<ul class="rli topic__items topic__section">
<li class="topic__item"><a href="/anthropology">Anthropology</a></li>
<li class="topic__item"><a href="/sustainability-science">Sustainability Science</a></li>
<li class="topic__item"><a href="/sustainable-development-goals" class="sdg-topic">Sustainable Development Goals</a></li>
</ul>
</div>
<div class="topics-tab__topic__article">
<h4 class="topic__heading">Articles By Topic</h4>
<div class="d-flex">
<ul class="rlist topic__items topic__section">
<li class="topic__item"><a href="/topic/demo">Demography</a></li>
<li class="topic__item"><a href="/topic/econ-sci">Economic Sciences</a></li>
<li class="topic__item"><a href="/environmental-sciences">Environmental Sciences</a></li>
</ul>
<ul class="rlist topic__items topic__section">
<li class="topic__item"><a href="/topic/pol-sci">Political Sciences</a></li>
<li class="topic__item"><a href="/psychological-and-cognitive-sciences">Psychological and Cognitive Sciences</a></li>
<li class="topic__item"><a href="/topic/soc-science">Social Sciences</a></li>
</ul>
</div>
</div>
</div>
</div><div id="nav-e657c77c-421c-46e0-b0a0-d72b63228a8b-biological-sciences-pane" aria-labelledby="nav-e657c77c-421c-46e0-b0a0-d72b63228a8b-biological-sciences-tab" role="tabpanel" class="tab-pane fade">



        
        <div class="topics-tab__topic">
<div class="topics-tab__topic__portal">
<h4 class="topic__heading">Featured Topic</h4>
<ul class="rli topic__items topic__section">
<li class="topic__item"><a href="/anthropology">Anthropology</a></li>
<li class="topic__item"><a href="/sustainability-science">Sustainability Science</a></li>
<li class="topic__item"><a href="/sustainable-development-goals" class="sdg-topic">Sustainable Development Goals</a></li>
</ul>
</div>
<div class="topics-tab__topic__article">
<h4 class="topic__heading">Articles By Topic</h4>
<div class="d-flex">
<ul class="rlist topic__items topic__section">
<li class="topic__item"><a href="/topic/ag-sci">Agricultural Sciences</a></li>
<li class="topic__item"><a href="/topic/app-bio">Applied Biological Sciences</a></li>
<li class="topic__item"><a href="/topic/biochem">Biochemistry</a></li>
<li class="topic__item"><a href="/biophysics-and-computational-biology">Biophysics and Computational Biology</a></li>
<li class="topic__item"><a href="/topic/cell-bio">Cell Biology</a></li>
<li class="topic__item"><a href="/topic/dev-bio">Developmental Biology</a></li>
<li class="topic__item"><a href="/topic/eco">Ecology</a></li>
<li class="topic__item"><a href="/environmental-sciences">Environmental Sciences</a></li>
<li class="topic__item"><a href="/topic/evolution">Evolution</a></li>
<li class="topic__item"><a href="/topic/genetics">Genetics</a></li>
</ul>
<ul class="rlist topic__items topic__section">
<li class="topic__item"><a href="/topic/immun">Immunology and Inflammation</a></li>
<li class="topic__item"><a href="/topic/med-sci">Medical Sciences</a></li>
<li class="topic__item"><a href="/topic/microbio">Microbiology</a></li>
<li class="topic__item"><a href="/topic/neuro">Neuroscience</a></li>
<li class="topic__item"><a href="/topic/pharm">Pharmacology</a></li>
<li class="topic__item"><a href="/topic/physio">Physiology</a></li>
<li class="topic__item"><a href="/topic/plant-bio">Plant Biology</a></li>
<li class="topic__item"><a href="/topic/pop-bio">Population Biology</a></li>
<li class="topic__item"><a href="/psychological-and-cognitive-sciences">Psychological and Cognitive Sciences</a></li>
<li class="topic__item"><a href="/topic/sys-bio">Systems Biology</a></li>
</ul>
</div>
</div>
</div>
</div></div>

        </div>
    

</div></div></li><li class="nav-item px-3"><div class="covidButton"></div></li></ul></div><div class="main-menu__right-content">



        
        <a href="#" aria-expanded="false" aria-label="Expand search field" aria-controls="quick-search-form-0" data-expand-label="Expand search field" data-collapse-label="Collapse search field" data-target=".header-quick-search" data-move-focus="#header-quick-search input" data-toggle="collapse" class="btn quick-search__trigger" title="Search"><svg xmlns="http://www.w3.org/2000/svg" width="45" height="45" viewBox="0 -8 32 50" class="quick-search-icon-animated"> <path d="M17.71,17.91a6.25,6.25,0,1,1,1.89-4.48,6.23,6.23,0,0,1-1.89,4.48" class="cls cls-1"></path> <line x1="25.07" y1="25.15" x2="8.2" y2="8.29" class="cls cls-2"></line> <line x1="8.2" y1="25.15" x2="25.07" y2="8.29" class="cls cls-3"></line></svg></a>




        
        















<div class="eCommerceCartIndicatorWidget">
    
        
        
            <a href="/action/showCart?FlowID=1" id="cartLabel" title="Cart" aria-labelledby="cartLabelText" class="shopping-cart-indicator">
                    <span class="position-relative d-flex mr-lg-3 mr-0 pt-1 pr-1 pt-lg-0 pr-lg-0">
                        <i aria-hidden="true" class="icon-shopping-cart"></i>
                        <span class="shopping-cart-indicator__badge  sr-only"
                              data-id="cart-size" id="cartLabelText" aria-live="polite">
                            <span class="sr-only">Shopping cart with </span>
                            <span class="cart-count">0</span>
                            <span class="sr-only"> item </span>
                        </span>
                    </span>
                <span class="shopping-cart-indicator__label font-weight-bold text-deep-gray">Cart</span>
            </a>
        
    
</div>




        
        




    








    
        




    







<div class="login-bar text-uppercase">
    <a href="/action/showLogin" class="font-weight-bold btn btn-outline-primary btn--light-outline btn-login collapsed" data-target=".login-bar__menu" data-toggle="collapse" aria-expanded="false">
        <span>Sign in</span>
    </a>
    
        
        
            <a href="/action/registration?redirectUri=%2Faction%2FcookieAbsent" class="font-weight-bold btn btn-primary btn-register">
                Register
            </a>
        
    

    <div id="login-bar__menu" class="login-bar__menu collapse" data-parent=".headerParentClass-e184595">
        <a href="/action/showLogin?redirectUri=%2Faction%2FcookieAbsent" class="login-bar__menu__login-option">
            Individual Login
        </a>
        <a href="/action/ssostart?redirectUri=%2Faction%2FcookieAbsent" class="login-bar__menu__login-option">
            Institutional Login
        </a>
    </div>
</div>
    
    






        
        <div class="d-flex align-items-center"><a href="https://www.pnascentral.org/cgi-bin/main.plex" class="font-weight-bold btn btn-primary btn-header-submit">Publish</a></div>
</div><!-- Institution Banner Dropzone for small devices--><div class="d-block d-xl-none"></div></div>
</div></nav><div data-parent=".headerParentClass-e184595" class="bg-black-gray header-quick-search collapse"><span class="arrow"></span><div class="quick-search--container">



        
        <div class="quick-search row no-gutters flex-column quick-search--header flex-column"><div class="quick-search__items col"><div aria-labelledby="trigger-quick-search-form-ba20dcbf-b159-41b6-a89e-49552f0ecc62-0" id="quick-search-form-ba20dcbf-b159-41b6-a89e-49552f0ecc62-0" data-parent=".quick-search__items" role="tabpanel" class="collapse show "><form action="/action/doSearch" name="defaultQuickSearch" method="get" id="header-quick-search"><fieldset><legend class="sr-only">Quick Search anywhere</legend><div class="input-group option-0   animation-underline"><label for="AllFieldba20dcbf-b159-41b6-a89e-49552f0ecc620" class="sr-only">Enter journal, DOI, article type, keywords, authors, etc.</label><input type="search" id="AllFieldba20dcbf-b159-41b6-a89e-49552f0ecc620" name="AllField" autocomplete="off" placeholder="Enter journal, DOI, article type, keywords, authors, etc." data-auto-complete-max-words="7" data-auto-complete-max-chars="32" data-contributors-conf="3" data-topics-conf="3" data-publication-titles-conf="3" data-history-items-conf="3" value="" class="quick-search__input form-control autocomplete"/><div class="input-group-append"></div></div></fieldset></form></div><div aria-labelledby="trigger-quick-search-form-ba20dcbf-b159-41b6-a89e-49552f0ecc62-1" id="quick-search-form-ba20dcbf-b159-41b6-a89e-49552f0ecc62-1" data-parent=".quick-search__items" role="tabpanel" class="collapse "><form action="/action/quickLink" name="citationQuickSearch" method="get"><fieldset class="row no-gutters"><legend class="sr-only">Quick search in Citations</legend><div class="input-group option-citation option-1"><label for="citationJournalDropdown" class="sr-only">Journal*</label><select name="quickLinkJournal" id="citationJournalDropdown" required="required" class="form-control animation-underline citationJournalDropdown"><option disabled="disabled" selected="selected" hidden="hidden" value="">Journal*</option><option value="nexus">PNAS Nexus</option><option value="pnas">Proceedings of the National Academy of Sciences</option></select><div class="citationSearch-wrapper"><label for="quickLinkYearba20dcbf-b159-41b6-a89e-49552f0ecc621" class="sr-only">Year</label><input type="search" id="quickLinkYearba20dcbf-b159-41b6-a89e-49552f0ecc621" name="quickLinkYear" autoComplete="false" placeholder="Year" class="form-control"/><label for="quickLinkVolumeba20dcbf-b159-41b6-a89e-49552f0ecc621" class="sr-only">Volume*</label><input type="search" id="quickLinkVolumeba20dcbf-b159-41b6-a89e-49552f0ecc621" name="quickLinkVolume" autoComplete="false" required="required" placeholder="Volume*" class="form-control"/><label for="quickLinkIssueba20dcbf-b159-41b6-a89e-49552f0ecc621" class="sr-only">Issue*</label><input type="search" id="quickLinkIssueba20dcbf-b159-41b6-a89e-49552f0ecc621" name="quickLinkIssue" autoComplete="false" required="required" placeholder="Issue*" class="form-control"/><label for="quickLinkPageba20dcbf-b159-41b6-a89e-49552f0ecc621" class="sr-only">Page/eLocation ID*</label><input type="search" id="quickLinkPageba20dcbf-b159-41b6-a89e-49552f0ecc621" name="quickLinkPage" autoComplete="false" required="required" placeholder="Page/eLocation ID*" class="form-control"/><input type="hidden" name="quickLink" value="true"/><div class="input-group-append"></div></div><div class="citation-annotation">*Required field</div><input type="submit" hidden="hidden" id="citationFormSubmit"/></div></fieldset></form></div><div aria-labelledby="trigger-quick-search-form-ba20dcbf-b159-41b6-a89e-49552f0ecc62-2" id="quick-search-form-ba20dcbf-b159-41b6-a89e-49552f0ecc62-2" data-parent=".quick-search__items" role="tabpanel" class="collapse "><form action="/action/doSearch" name="publicationQuickSearch" method="get" id="header-quick-search-2"><fieldset><legend class="sr-only">Quick Search in Journals</legend><div class="input-group option-2 option-journal  animation-underline"><label for="AllFieldba20dcbf-b159-41b6-a89e-49552f0ecc622" class="sr-only">Enter journal, DOI, article type, keywords, authors, etc.</label><input type="search" id="AllFieldba20dcbf-b159-41b6-a89e-49552f0ecc622" name="AllField" autocomplete="off" placeholder="Enter journal, DOI, article type, keywords, authors, etc." data-auto-complete-max-words="7" data-auto-complete-max-chars="32" data-contributors-conf="3" data-topics-conf="3" data-publication-titles-conf="3" data-history-items-conf="3" value="" class="quick-search__input form-control autocomplete"/><input type="hidden" name="SeriesKey" value="nexus"/><div class="input-group-append"></div></div></fieldset></form></div><div aria-labelledby="trigger-quick-search-form-ba20dcbf-b159-41b6-a89e-49552f0ecc62-3" id="quick-search-form-ba20dcbf-b159-41b6-a89e-49552f0ecc62-3" data-parent=".quick-search__items" role="tabpanel" class="collapse "><form action="/action/doSearch" name="publicationQuickSearch" method="get" id="header-quick-search-3"><fieldset><legend class="sr-only">Quick Search in Journals</legend><div class="input-group option-3 option-journal  animation-underline"><label for="AllFieldba20dcbf-b159-41b6-a89e-49552f0ecc623" class="sr-only">Enter journal, DOI, article type, keywords, authors, etc.</label><input type="search" id="AllFieldba20dcbf-b159-41b6-a89e-49552f0ecc623" name="AllField" autocomplete="off" placeholder="Enter journal, DOI, article type, keywords, authors, etc." data-auto-complete-max-words="7" data-auto-complete-max-chars="32" data-contributors-conf="3" data-topics-conf="3" data-publication-titles-conf="3" data-history-items-conf="3" value="" class="quick-search__input form-control autocomplete"/><input type="hidden" name="SeriesKey" value="pnas"/><div class="input-group-append"></div></div></fieldset></form></div></div><div class="row no-gutters justify-content-end align-items-center quick-search__actions flex-column flex-sm-row"><div class="col d-flex align-items-center flex-grow-1"><label class="mb-0 text-uppercase dropdown-selectable__label mr-2">Searching:</label><div class="d-flex align-items-center flex-fill "><div class="quick-search__dropdown dropdown dropdown-selectable"><button id="dropdownMenuButton" type="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false" class="btn dropdown-toggle">Anywhere</button><div aria-labelledby="dropdownMenuButton" role="tablist" class="dropdown-menu"><a href="#quick-search-form-ba20dcbf-b159-41b6-a89e-49552f0ecc62-0" id="trigger-quick-search-form-ba20dcbf-b159-41b6-a89e-49552f0ecc62-0" data-toggle="collapse" class="dropdown-item  active">Anywhere</a><a href="#quick-search-form-ba20dcbf-b159-41b6-a89e-49552f0ecc62-1" id="trigger-quick-search-form-ba20dcbf-b159-41b6-a89e-49552f0ecc62-1" data-toggle="collapse" class="dropdown-item">Citation</a><a href="#quick-search-form-ba20dcbf-b159-41b6-a89e-49552f0ecc62-2" id="trigger-quick-search-form-ba20dcbf-b159-41b6-a89e-49552f0ecc62-2" data-toggle="collapse" class="dropdown-item">PNAS Nexus</a><a href="#quick-search-form-ba20dcbf-b159-41b6-a89e-49552f0ecc62-3" id="trigger-quick-search-form-ba20dcbf-b159-41b6-a89e-49552f0ecc62-3" data-toggle="collapse" class="dropdown-item">Proceedings of the National Academy of Sciences</a></div></div></div></div><div class="col justify-content-end d-flex align-items-center quick-search__buttons">



        
        <a href="/search/advanced" class="text-white text-uppercase mini-title quick-search__advanced">Advanced Search</a>
<button type="submit" form="header-quick-search" title="Search" class="quick-search__btn btn d-flex btn-primary align-items-center justify-content-center justify-content-sm-between mb-3 mb-sm-0"><span class="font-weight-bold text-uppercase mini-title">Search</span><i class="icon-arrow-right align-middle ml-2"></i></button></div></div></div>




        
        <div class="suggested-searches">



        
        <div class="suggested-searches__title">SUGGESTED SEARCHES: </div>
<div class="suggested-searches__search-words">
    <a href="/action/doSearch?AllField=covid+19" class="suggested-searches__search-word">Covid-19</a>
    <a href="/action/doSearch?AllField=artificial+intelligence" class="suggested-searches__search-word">Artificial Intelligence</a>
    <a href="/action/doSearch?AllField=mpox" class="suggested-searches__search-word">Mpox</a>
    <a href="/action/doSearch?AllField=climate+change" class="suggested-searches__search-word">Climate Change</a>
    <a href="/action/doSearch?AllField=gun+violence" class="suggested-searches__search-word">Gun Violence</a>
</div>
</div>
</div></div><section aria-label="slider-menu" id="slider-side-menu" class="slider"><div class="slider__container"><div id="screen-side-navigation" class="slider__screen slider__screen--root"><div class="slider__screen__content"><div class="side-menu px-3"><div class="side-menu__user-login-bar"></div><div class="side-menu__quick-search">



        
        <div class="quick-search row no-gutters"><div class="col quick-search__sidebar"><form action="/action/doSearch" name="defaultQuickSearch" method="get" id="quick-search-from-85eb734f-3d8c-4802-b914-d40de047cf3c0" role="search"><fieldset><legend class="sr-only">Quick Search anywhere</legend><div class="input-group option-0  align-items-center  animation-underline animation-underline--primary"><label for="AllField85eb734f-3d8c-4802-b914-d40de047cf3c0" class="sr-only">Enter journal, DOI, article type, keywords, authors, etc.</label><input type="search" id="AllField85eb734f-3d8c-4802-b914-d40de047cf3c0" name="AllField" autocomplete="off" placeholder="Enter journal, DOI, article type, keywords, authors, etc." data-auto-complete-max-words="7" data-auto-complete-max-chars="32" data-contributors-conf="3" data-topics-conf="3" data-publication-titles-conf="3" data-history-items-conf="3" value="" class="quick-search__input form-control autocomplete"/><div class="input-group-append"><button type="submit" title="Search" class="btn quick-search__btn p-0"><i class="icon-search align-middle"></i></button></div></div></fieldset></form></div></div>
</div><div class="side-menu__nav-menu"></div><div class="side-menu__extra-nav"></div><div class="side-menu__menu-footer">









    
    
        <footer data-widget-def="UX3HTMLWidget" data-widget-id="c1d89ee2-d7e8-41ac-9c96-6105d574b1d8">
        



        
        <a href="/" class="footer-logo"> <img src="/pb-assets/images/Logos/header-logo/logo-1624644560537.svg" alt="PNAS"> </a>
<div class="footer__social-media__wrapper d-flex mt-3">
<div class="footer__social-media">
<ul role="list" class="list-inline footer__social-media__list text-center d-flex flex-wrap">
<li role="listitem" class="list-inline-item footer__social-media__list-item"><a href="https://www.facebook.com/pages/PNAS/18262365099" title="Facebook" class="d-block"> <i class="icon-facebook" aria-hidden="true"></i> </a></li>
<li role="listitem" class="list-inline-item footer__social-media__list-item"><a href="https://twitter.com/PNASNews" title="Twitter" class="d-block"> <i aria-hidden="true"><img src="/pb-assets/images/icons/twitter-x-gray-1705527808743.svg"></i> </a></li>
<li role="listitem" class="list-inline-item footer__social-media__list-item"><a href="https://bsky.app/profile/pnas.org" title="Bluesky" class="d-block" style="line-height: 118%;"> <i aria-hidden="true"> <img src="/pb-assets/images/icons/icon-bluesky-mobile-1734362341180.png"></i> </a></li>
<li role="listitem" class="list-inline-item footer__social-media__list-item"><a href="https://www.youtube.com/channel/UCYjvFEQMgH6ou8fSYfiOKCw" title="Youtube" class="d-block"> <i class="icon-youtube" aria-hidden="true"></i> </a></li>
<li role="listitem" class="list-inline-item footer__social-media__list-item"><a href="https://www.linkedin.com/showcase/pnas-news/" title="LinkedIn" target="_blank" class="d-block" rel="noopener"> <i class="icon-LinkedIn2" aria-hidden="true"></i></a></li>
<li role="listitem" class="list-inline-item footer__social-media__list-item"><a href="/action/showPreferences?menuTab=Alerts" title="Mail" class="d-block"> <i class="icon-mail" aria-hidden="true"></i> </a></li>
<li role="listitem" class="list-inline-item footer__social-media__list-item"><a href="/about/rss" title="RSS feeds" class="d-block"> <i class="icon-rss" aria-hidden="true"></i> </a></li>
</ul>
</div>
</div>
<div class="footer__links"><a href="/about/staff-directory">Contact</a> <a href="/about/site-map">Site Map</a> <a href="/about/terms">Terms &amp; Privacy Policy</a> <a href="/about/accessibility">Accessibility</a></div>

        </footer>
    

</div></div></div></div></div></section></header>




        
        <div class="container-fluid"><div class="row"><main class="content w-100 text-center">



        
        
<style>.pb-edit-view .page-top-banner{display: none !important;}</style>
<div class="page-top-banner row justify-content-center">
<div class="col-12 px-0">
<h1 class="main-title text-center mb-0 mb-md-5 py-5 border-bottom">      </h1>
</div>
</div>

</main></div></div>




        
        









    
    
        <section data-widget-def="ux3-layout-widget" data-widget-id="a20ca6a1-603b-499e-81db-ee1dc31f5224" class="signup-ad" aria-label="signup-ad">
        



        
        <div class="signup-ad__container">



        
        <h3 class="signup-ad__title">Sign up for the<span class="d-block"><em>PNAS Highlights</em> newsletter</span></h3>

<p class="align-center pt-3"><a href="/pnas-highlights" class="btn btn-primary">Subscribe for Research Updates</a></p>


</div>

        </section>
    

<footer class="footer pb-3"><section class="footer__top py-3"><div class="container-fluid"><div class="row align-items-center"><div class=" col-sm-6 col-md-4 my-4 d-flex justify-content-center flex-column">



        
        <a href="/" title="PNAS logo" class="footer__logo-wrapper">
    <img src="/pb-assets/images/Logos/footer/logo-footer-1624408444100.svg
" alt="PNAS logo" class="footer__logo">
</a>




        
        <p><link crossorigin="anonymous" href="https://use.fontawesome.com/releases/v5.12.1/css/all.css" rel="stylesheet"></p>
<div class="footer__social-media__wrapper d-flex mt-3">
<div class="footer__social-media">
<ul role="list" class="list-inline footer__social-media__list text-center d-flex flex-wrap">
<li role="listitem" class="list-inline-item footer__social-media__list-item"><a href="https://www.facebook.com/pages/PNAS/18262365099" title="Facebook" target="_blank" rel="noopener"><i class="icon-facebook" aria-hidden="true"></i></a></li>
<li role="listitem" class="list-inline-item footer__social-media__list-item"><a href="https://twitter.com/PNASNews" title="X" target="_blank" rel="noopener"><i class="icon-twitter" aria-hidden="true"></i></a></li>
<li role="listitem" class="list-inline-item footer__social-media__list-item"><a href="https://bsky.app/profile/pnas.org" title="Bluesky" target="_blank" rel="noopener"><i class="icon-bluesky" aria-hidden="true"></i></a></li>
<li role="listitem" class="list-inline-item footer__social-media__list-item"><a href="https://www.youtube.com/channel/UCYjvFEQMgH6ou8fSYfiOKCw" title="Youtube" target="_blank" rel="noopener"><i class="icon-youtube" aria-hidden="true"></i></a></li>
<li role="listitem" class="list-inline-item footer__social-media__list-item"><a href="https://www.linkedin.com/showcase/pnas-news/" title="LinkedIn" target="_blank" rel="noopener"><i class="icon-LinkedIn2" aria-hidden="true"></i></a></li>
<li role="listitem" class="list-inline-item footer__social-media__list-item"><a href="/email-alerts-and-rss" title="Mail"><i class="icon-mail" aria-hidden="true"></i></a></li>
<li role="listitem" class="list-inline-item footer__social-media__list-item"><a href="/about/rss" title="RSS feeds"><i class="icon-rss" aria-hidden="true"></i></a></li>
</ul>
</div>
</div> 
</div><div class=" col-sm-6 col-md-4 my-4 text-uppercase font-weight-bold">



        
        <style>
  .headerlist {
          font-size: 17px;
          font-weight: bold;
          text-align: left;
          margin-bottom: .7rem;
      }
  .footer__sitemap__list-item {
          text-align: left;
          font-weight: 600;
      }
</style>
<div class="footer__sitemap">
<div class="headerlist">Browse</div>
<ul role="list" class="list-unstyled footer__sitemap__list text-center">
<li role="listitem" class="footer__sitemap__list-item"><a href="/toc/pnas/current" title="Current Issue" class="animation-underline">Current Issue</a></li>
<li role="listitem" class="footer__sitemap__list-item my-2"><a href="https://academic.oup.com/pnasnexus" title="PNAS Nexus" class="animation-underline"><em>PNAS Nexus</em></a></li>
<li role="listitem" class="footer__sitemap__list-item my-2"><a href="/about/special-features" title="List of Issues" class="animation-underline">Special Features</a></li>
<li role="listitem" class="footer__sitemap__list-item my-2"><a href="/loi/pnas" title="List of Issues" class="animation-underline">List of Issues</a></li>
<li role="listitem" class="footer__sitemap__list-item my-2"><a href="/about/topics-collections-article-types" title="Collected Papers" class="animation-underline">Topics, Collections, and Article Types</a></li>
<li role="listitem" class="footer__sitemap__list-item my-2"><a href="/about/pnas-in-the-news" title="PNAS In The News" class="animation-underline">PNAS In The News</a></li>
<li role="listitem" class="footer__sitemap__list-item my-2"><a href="/front-matter" title="Front Matter" class="animation-underline">Front Matter</a></li>
<li role="listitem" class="footer__sitemap__list-item my-2"><a href="/journal-club" title="Journal Club" class="animation-underline">Journal Club</a></li>
<li role="listitem" class="footer__sitemap__list-item my-2"><a href="/multimedia" title="List of Issues" class="animation-underline">Multimedia</a></li>
<li role="listitem" class="footer__sitemap__list-item my-2"><a href="/about/science-sessions-podcast" title="Podcasts" class="animation-underline">Podcasts</a></li>
</ul>
</div>
</div><div class=" col-sm-6 col-md-4 my-4 text-uppercase font-weight-bold">



        
        <style>
        .headerlist { 
                font-size: 17px;
                font-weight: bold;
                text-align: left; 
                margin-bottom: .7rem;
            },
            .footer__sitemap__list-item { 
                    text-align: left;
                    font-weight: 600;
                }
        </style>
<div class="footer__sitemap">
<div class="headerlist">Information</div>
<ul role="list" class="list-unstyled footer__sitemap__list text-center">
<li role="listitem" class="footer__sitemap__list-item"><a href="/about" title="About" class="animation-underline">About</a></li>
<li role="listitem" class="footer__sitemap__list-item my-2"><a href="/sustainable-development-goals" title="Sustainable Development Goals" class="animation-underline">Sustainable Development Goals</a></li>
<li role="listitem" class="footer__sitemap__list-item my-2"><a href="/about/editorial-board" title="Editorial Board" class="animation-underline">Editorial Board</a></li>
<li role="listitem" class="footer__sitemap__list-item my-2"><a href="/author-center" title="Authors" class="animation-underline">Authors</a></li>
<li role="listitem" class="footer__sitemap__list-item my-2"><a href="/reviewer" title="Reviewers" class="animation-underline">Reviewers</a></li>
<li role="listitem" class="footer__sitemap__list-item my-2"><a href="/subscriptions" title="Suscribers" class="animation-underline">Subscribers</a></li>
<li role="listitem" class="footer__sitemap__list-item my-2"><a href="/librarians" title="Librarians" class="animation-underline">Librarians</a></li>
<li role="listitem" class="footer__sitemap__list-item my-2"><a href="/about/press" title="Press" class="animation-underline">Press</a></li>
<li role="listitem" class="footer__sitemap__list-item my-2"><a href="/about/cozzarelli-prize" title="Cozzarelli Prize" class="animation-underline">Cozzarelli Prize</a></li>
<li role="listitem" class="footer__sitemap__list-item my-2"><a href="/updates" title="PNAS Updates" class="animation-underline">PNAS Updates</a></li>
</ul>
</div>
</div></div></div><div data-show-after="400" class="back-to-top back-to-top--align-right  "><button data-snap="footer__top" aria-label="back to top" class="back-to-top__action position-relative p-0 m-0 border-0 d-flex flex-column align-items-center justify-content-center"><svg viewBox="0 0 36 36" class="position-relative"><path d="M18 2.0845 a 15.9155 15.9155 0 0 1 0 31.831 a 15.9155 15.9155 0 0 1 0 -31.831" class="back-to-top__action__ring-bg"></path><path d="M18 2.0845 a 15.9155 15.9155 0 0 1 0 31.831 a 15.9155 15.9155 0 0 1 0 -31.831" stroke-dasharray="0, 100" class="back-to-top__action__ring"></path></svg><span class="back-to-top__action-icon position-absolute d-flex"><i aria-hidden="true" class="icon-arrow-up"></i></span><span class="sr-only">Back to top</span></button></div></section><section class="footer__bottom"><div class="container-100"><div class="row align-items-center"><div class="col-md-8 col-sm-10">



        
        <div class="footer__copyright text-center text-sm-left px-sm-0 px-4"><p class="m-0">Copyright © 2026 National Academy of Sciences. All rights reserved. | Online ISSN 1091-6490</p><p class="m-0">PNAS is a partner of CHORUS, CLOCKSS, COPE, Crossref, ORCID, and Research4Life.</p></div>
</div><div class="col-md-4 col-sm-2 text-sm-right text-center mt-sm-0 mt-3">



        
        <ul role="list" class="list-inline footer__copyright__links">
    <li role="listitem" class="list-inline-item">
        <a href="/about/staff-directory" title="Contact">Contact</a>
	</li>
	<li role="listitem" class="list-inline-item">
        <a href="/about/site-map" title="Site Map">Site Map</a>
	</li>
	<li role="listitem" class="list-inline-item">
        <a href="/about/terms" title="Terms">Terms &amp; Privacy Policy</a>
	</li>
        <li class="list-inline-item">
        <a href="/about/accessibility" title="Accessibility">Accessibility</a>
    </li>
</ul>
</div></div></div></section></footer>




        
        <aside class="cookie-policy"> <p>We use cookies on this site to enhance your user experience. By using this website, you are giving your consent for us to set cookies. <a href="/help/cookie-policy">Find out more</a></p><a href="/help/cookie-policy" class="btn btn-primary">CONTINUE</a></aside>




        
        




<div class="modal fade" role="dialog" tabindex="-1" id="modal--requestUsername">
    <div class="modal-dialog modal-fullscreen-sm-down" role="document">
        <div class="modal-content content">
            <div class="modal-header">
                <h2 class="modal-title h5">Request Username</h2>
                <button type="button" data-dismiss="modal" aria-label="close" class="close">
                    <span aria-hidden="true">x</span>
                    <span class="sr-only">Close</span>
                </button>
            </div>
            <div class="modal-body">
                <form action="/action/requestUsername" class="raa-form" method="post"><input type="hidden" name="requestUsername" value="requestUsername" />
                    <p>Can't sign in? Forgot your username? <br />
                        Enter your email address below and we will send you your username</p>
                    <div class="alert alert-danger d-none"></div>

                    <div class="form-row">
                        <div class="col">
                            <div class="form-group">
                                <label for="6eccc267-4bd8-4882-88e8-d9b06094352c.email">Email</label>
                                <input id="6eccc267-4bd8-4882-88e8-d9b06094352c.email" class="form-control" type="text" name="email" value="" size="15" />
                            </div>
                        </div>
                    </div>
                    
                        <div class="form-row">
                            <div class="col">
                                <div class="form-group">
                                    <div class="username-recaptcha-ajax"></div>
                                </div>
                            </div>
                        </div>
                    

                    <div class="form-row">
                        <div class="col text-right">
                            <button type="submit" data-dismiss="modal" class="btn btn-submit">
                                <span>Submit</span>
                                <span aria-hidden="true" class="icon-arrow-right ml-3"></span>
                            </button>
                        </div>
                    </div></form>

                <div class="alert alert-success d-none">
                    <p>If the address matches an existing account you will receive an email with instructions to retrieve your username</p>
                </div>

            </div>
        </div>
    </div>
</div>




        
        





<div tabindex="-1" id="modal--registration" aria-labelledby="modalRegistrationLabel" class="modal fade" aria-modal="true" role="dialog">
    <div role="document" class="modal-dialog modal-fullscreen-sm-down">
        <div class="modal-content content">
            <div class="modal-header">
                <h2 id="modalRegistrationLabel" class="modal-title h5">Create a new account</h2>
                <button type="button" data-dismiss="modal" aria-label="close" class="close">
                    <span aria-hidden="true">x</span><span class="sr-only">Close</span>
                </button>
            </div>
            <div class="modal-body">
                <form action="/action/registration" class="registration-form raa-form" method="post"><input type="hidden" name="redirectUri" value="/action/cookieAbsent" />
                    <div class="form-row">
                        <div class="col">
                            <div class="form-group">
                                <label for="f96c9a0d-f4a9-4ca3-a52b-99fb097c56d6.email">Email</label>
                                <input id="f96c9a0d-f4a9-4ca3-a52b-99fb097c56d6.email" class="email form-control" type="email" name="email" value=""required="required" />
                            </div>
                        </div>
                    </div>
                    <div class="form-row">
                        <div class="col-12 col-sm-6">
                            <a href="/action/showLogin" class="show-login">
                                
                                Returning user
                            </a>
                        </div>
                        <div class="col text-right">
                            <button type="submit" data-dismiss="modal" class="btn btn-submit">
                                <span>Submit</span>
                                <span aria-hidden="true" class="icon-arrow-right ml-3"></span>
                            </button>
                        </div>
                    </div></form>
            </div>
        </div>
    </div>
</div>




        
        














<div tabindex="-1" id="modal--login" aria-labelledby="modalLoginLabel" class="modal fade" aria-modal="true" role="dialog">
    <div role="document" class="modal-dialog modal-fullscreen-sm-down">
        <div class="modal-content content">
            <div class="modal-header">
                <h2 id="modalLabelLogin" class="modal-title h5">Login</h2>
                <button type="button" data-dismiss="modal" aria-label="close" class="close">
                    <span aria-hidden="true">x</span><span class="sr-only">Close</span>
                </button>
            </div>
            




















<div class="modal-body">
    <form action="/action/doLogin" id="loginForm" class="raa-form login-form " method="post"><input type="hidden" name="id" value="465aa1e9-3090-4f74-8ca8-f0d260f07eeb" />
        





    
    
        <input type="hidden" name="redirectUri" value="/action/cookieAbsent" />
    


<input type="hidden" name="loginUri" value="/action/cookieAbsent" />
        
            <input type="hidden" name="popup" value="true" />
        
        
            
            
                <div class="form-row">
                    <div class="col-12 col-sm-6">
                        <div class="form-group">
                            



























    
        
    
    
        
    
    
    
        
    

        

        
    <div class="form-group">
        <div class="label ">

            
                
                
                
                    <label for="login">Email<span class="required-marker" aria-hidden="true">*</span></label>
                
            
            
        </div>
        
        
        <input id="login" class="form-control" type="text" name="login" value="" size="15" autocomplete="" placeholder="Enter your email"aria-required="true" />
        
                            
    </div>

                        </div>
                        <div class="actions raa-form__reset-password text-right mt-n4">
                            
                        </div>
                    </div>

                    <div class="col">
                        <div class="form-group">
                            






















    



    
    
    <div class="form-group">
        <div class="label ">
            <label for="password">Password<span class="required-marker"
                                                                                        aria-hidden="true">*</span></label>
            
        </div>
        
        
        <input id="password" class="form-control" type="password" name="password" value="" autocomplete="off" placeholder="Enter your password"aria-required="true" />
        <span role="button" class="password-eye-icon icon-eye apply-btn hidden" aria-label="Show password" tabindex="0" onclick="togglePassword(this)" onkeydown="handleKey(event,this)"></span>
        
                            
    </div>
    <script>
        function togglePassword(el) {
            const passwordInput = document.getElementById("password");
            const isHidden = passwordInput.type === "password";

            // Toggle password visibility
            passwordInput.type = isHidden ? "text" : "password";

            // Safely update the aria-label and classes
            if (el) {
                if (isHidden) {
                    el.setAttribute("aria-label", "Hide password");
                } else {
                    el.setAttribute("aria-label", "Show password");
                }
            }
        }

        function handleKey(event, el) {
            if (event.key === "Enter" || event.key === " ") {
                event.preventDefault();
                togglePassword(el);
            }
        }
    </script>

                        </div>
                        <div class="raa-form__reset-password text-right">
                            <span>Forgot your password? Reset it </span>
                            <a href="/action/requestResetPassword" type="button" data-target="#modal--resetPassword" data-toggle="modal" data-dismiss="modal">here</a>
                        </div>
                    </div>
                </div>
            
        
        <div class="form-row mt-4">
            <div class="col-12 col-sm-6 text-left">
                <div class="custom-control custom-checkbox">
                    
                        
                        
                            <input id="465aa1e9-3090-4f74-8ca8-f0d260f07eeb-remember" class="custom-control-input" type="checkbox" name="remember" value="true" />
                        
                    
                    <label for="465aa1e9-3090-4f74-8ca8-f0d260f07eeb-remember" class="custom-control-label">
                        Keep me logged in
                    </label>
                </div>
            </div>
            
                
                    <div class="col text-right">
                        <button type="submit" class="btn btn-submit">
                            <span>Login</span>
                            <span aria-hidden="true" class="icon-arrow-right ml-3"></span>
                        </button>
                    </div>
                
                
            
        </div>
        <div class="form-row border-top mt-3 pt-3">
            <div class="col raa-form__register">
                <span>Don’t have an account? Register</span>
                <a href="/action/registration">
                    here
                </a>
                
                    <a href="/action/ssostart?redirectUri=%2Faction%2FcookieAbsent" class="float-right">
                        
                        <div class="institution-login">
                            Institutional Login
                        </div>
                    </a>
                
                
            </div>
        </div></form>
</div>
        </div>
    </div>
</div>




        
        




<div tabindex="-1" id="modal--verifyPhone"
     aria-labelledby="modalverifyPhoneLabel"
     class="modal fade" aria-modal="true" role="dialog">
    <div role="document" class="modal-dialog modal-fullscreen-sm-down">
        <div class="modal-content">
            <div class="modal-header">
                <h2 id="modalverifyPhoneLabel" class="modal-title h5">Change Password </h2>
                <button type="button" data-dismiss="modal" aria-label="close" class="close">
                    <span aria-hidden="true">x</span><span class="sr-only">Close</span>
                </button>
            </div>

            <div class="modal-body">
                <form action="/action/verifyPhoneNumber" method="post"><input type="hidden" name="submit" value="submit" />
                    <div class="alert alert-danger d-none"></div>
                    <div class="form-row">
                        <div class="col">
                            <div class="form-group">
                                <label for="946b33a7-d695-4878-8fb4-546789ae57b3-code">Enter the verification code</label>
                                <input id="946b33a7-d695-4878-8fb4-546789ae57b3-code" class="form-control" type="text" name="verificationCode" value="" size="15"pattern="^[0-9]{6}$"required="required" />
                            </div>
                        </div>
                    </div>
                    <div class="form-row">
                        <div class="col text-right">
                            <button type="submit" class="btn btn-submit">
                                <span>Submit</span>
                                <span aria-hidden="true" class="icon-arrow-right ml-3"></span>
                            </button>
                        </div>
                    </div></form>
            </div>

        </div>
        <div class="alert alert-success d-none">
            <h5>Congrats!</h5>
            <p>Your Phone has been verified</p>
        </div>
    </div>
</div>
</div>

                    
                
            </div>
        </div>
                
        

            <script src="/products/pnas/releasedAssets/js/build.lazyload.bundle-a98ba55ef986477294a0.js" nonce="9e82adca2a003ea1-ARN"></script>

        <script src="/products/pnas/releasedAssets/js/main.bundle-44d1642b04d51b802818.js"  nonce="9e82adca2a003ea1-ARN"></script>
        

















    <script type="text/javascript" nonce="9e82adca2a003ea1-ARN">
        $(document).ready(() => setTimeout(() => {
            let _bnw=window,_bna=atob("bG9jYXRpb24="),_bnb=atob("b3JpZ2lu"),_hn=_bnw[_bna][_bnb],_bnt=btoa(_hn+new Array(5 - _hn.length % 4).join(" "));
            $.get("/resource/lodash?t="+_bnt);
        },4000));
    </script>













    

    
    

    
    
    
    


    


            <script>(function(){function c(){var b=a.contentDocument||a.contentWindow.document;if(b){var d=b.createElement('script');d.innerHTML="window.__CF$cv$params={r:'9e82adca2a003ea1',t:'MTc3NTQ5ODI4Ny4wMDAwMDA='};var a=document.createElement('script');a.nonce='';a.src='/cdn-cgi/challenge-platform/scripts/jsd/main.js';document.getElementsByTagName('head')[0].appendChild(a);";b.getElementsByTagName('head')[0].appendChild(d)}}if(document.body){var a=document.createElement('iframe');a.height=1;a.width=1;a.style.position='absolute';a.style.top=0;a.style.left=0;a.style.border='none';a.style.visibility='hidden';document.body.appendChild(a);if('loading'!==document.readyState)c();else if(window.addEventListener)document.addEventListener('DOMContentLoaded',c);else{var e=document.onreadystatechange||function(){};document.onreadystatechange=function(b){e(b);'loading'!==document.readyState&&(document.onreadystatechange=e,c())}}}})();</script></body>
        
        
    

</html>