Ratio of males to females in a population

<span class="mw-page-title-main">Sex ratio</span>

Sex ratio

<p>A <b>sex ratio</b> is the <a href="/en/Ratio" title="Ratio" class="wl">ratio</a> of <a href="/en/Male" title="Male" class="wl">males</a> to <a href="/en/Female" title="Female" class="wl">females</a> in a <a href="/en/Population" title="Population" class="wl">population</a>. As explained by <a href="/en/Fisher's_principle" title="Fisher's principle" class="wl">Fisher's principle</a>, for evolutionary reasons this is typically about 1:1 in species which reproduce <a href="/en/Sexual_reproduction" title="Sexual reproduction" class="wl">sexually</a>.<span class="mw-ref reference" id="cite_ref-Fisher_2-0"><a href="#cite_note-Fisher-2" style="counter-reset: mw-Ref 2;"><span class="mw-reflink-text">[2]</span></a></span><span class="mw-ref reference" id="cite_ref-Hamilton_3-0"><a href="#cite_note-Hamilton-3" style="counter-reset: mw-Ref 3;"><span class="mw-reflink-text">[3]</span></a></span> However, many species deviate from an even sex ratio, either periodically or permanently. Examples include <a href="/en/Parthenogenic" title="Parthenogenic" class="mw-redirect wl">parthenogenic</a> species, periodically mating organisms such as aphids, some <a href="/en/Eusociality" title="Eusociality" class="wl">eusocial</a> <a href="/en/Wasp" title="Wasp" class="wl">wasps</a>, <a href="/en/Bee" title="Bee" class="wl">bees</a>, <a href="/en/Ant" title="Ant" class="wl">ants</a>, and <a href="/en/Termite" title="Termite" class="wl">termites</a>.<span class="mw-ref reference" id="cite_ref-4"><a href="#cite_note-4" style="counter-reset: mw-Ref 4;"><span class="mw-reflink-text">[4]</span></a></span></p>

<div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none" about="#mwt1">Ratio of males to females in a population</div>
<style data-mw-deduplicate="TemplateStyles:r1033289096" typeof="mw:Extension/templatestyles mw:Transclusion">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}</style>
<figure class="wiki-thumb"><a href="/en/File:Sex_ratio_total_population_2020.svg" class="mw-file-description image media-thumb" data-hash="File:Sex_ratio_total_population_2020.svg"><img loading="lazy" src="//upload.wikimedia.org/wikipedia/commons/thumb/a/ab/Sex_ratio_total_population_2020.svg/300px-Sex_ratio_total_population_2020.svg.png" decoding="async" data-file-width="2911" data-file-height="1297" data-file-type="drawing" height="134" width="300" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/a/ab/Sex_ratio_total_population_2020.svg/450px-Sex_ratio_total_population_2020.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/a/ab/Sex_ratio_total_population_2020.svg/600px-Sex_ratio_total_population_2020.svg.png 2x" alt="Sex_ratio_total_population_2020.svg"></a><figcaption>Map indicating the human sex ratio by country.<span class="mw-ref reference" id="cite_ref-1"><a href="#cite_note-1" style="counter-reset: mw-Ref 1;"><span class="mw-reflink-text">[1]</span></a></span>
<table width="100%" border="0" cellspacing="0" cellpadding="0" style="background:transparent">
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<style data-mw-deduplicate="TemplateStyles:r981673959" typeof="mw:Extension/templatestyles mw:Transclusion">.mw-parser-output .legend{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .legend-color{display:inline-block;min-width:1.25em;height:1.25em;line-height:1.25;margin:1px 0;text-align:center;border:1px solid black;background-color:transparent;color:black}.mw-parser-output .legend-text{}</style><div class="legend" about="#mwt6"><span class="legend-color mw-no-invert" style="background-color:#E66771; color:black;"><span>&nbsp;</span></span><span>&nbsp;</span>Countries with more <b>males</b> than females.</div>
<div class="legend" about="#mwt9"><span class="legend-color mw-no-invert" style="background-color:#7CFC00; color:black;"><span>&nbsp;</span></span><span>&nbsp;</span>Countries with the <b>same</b> number of males and females (accounting that the ratio has 3 <a href="/en/Significant_figures" title="Significant figures" class="wl">significant figures</a>, i.e., 1.00 males to 1.00 females).</div>
<div class="legend" about="#mwt12"><span class="legend-color mw-no-invert" style="background-color:#318CE7; color:black;"><span>&nbsp;</span></span><span>&nbsp;</span>Countries with more <b>females</b> than males.</div>
<div class="legend" about="#mwt15"><span class="legend-color mw-no-invert" style="background-color:Grey; color:black;"><span>&nbsp;</span></span><span>&nbsp;</span>No data</div></td></tr>
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<p>The <a href="/en/Human_sex_ratio" title="Human sex ratio" class="wl">human sex ratio</a> is of particular interest to anthropologists and demographers. In human societies, sex ratios at birth may be considerably skewed by factors such as the age of mother at birth<span class="mw-ref reference" id="cite_ref-cdc_5-0"><a href="#cite_note-cdc-5" style="counter-reset: mw-Ref 5;"><span class="mw-reflink-text">[5]</span></a></span> and by <a href="/en/Sex-selective_abortion" title="Sex-selective abortion" class="wl">sex-selective abortion</a> and infanticide. Exposure to pesticides and other environmental contaminants may be a significant contributing factor as well.<span class="mw-ref reference" id="cite_ref-6"><a href="#cite_note-6" style="counter-reset: mw-Ref 6;"><span class="mw-reflink-text">[6]</span></a></span> As of 2014, the global sex ratio at birth is estimated at 107 boys to 100 girls (1,000 boys per 934 girls).<span class="mw-ref reference" id="cite_ref-7"><a href="#cite_note-7" style="counter-reset: mw-Ref 7;"><span class="mw-reflink-text">[7]</span></a></span>.</p>



A sex ratio is the ratio of males to females in a population. As explained by Fisher's principle, for evolutionary reasons this is typically about 1:1 in species which reproduce sexually. The human sex ratio is of particular interest to anthropologists and demographers. In human societies, sex ratios at birth may be considerably skewed by factors such as the age of mother at birth. 