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The theory that natural selection should favour female offspring under suboptimal environmental conditions implies that pathogens may affect secondary sex ratio (ratio of male to female births). Using regression models containing 13 potential confounding factors, we have found that variation of the secondary sex ratio can be predicted by seroprevalence of <jats:italic>Toxoplasma<\/jats:italic> across 94 populations distributed across African, American, Asian and European continents. <jats:italic>Toxoplasma<\/jats:italic> seroprevalence was the third strongest predictor of secondary sex ratio, <jats:italic>\u03b2<\/jats:italic> = \u22120\u00b7097, <jats:italic>P<\/jats:italic> &lt; 0\u00b701, after son preference, <jats:italic>\u03b2<\/jats:italic> = 0\u00b7261, <jats:italic>P<\/jats:italic> &lt; 0\u00b705, and fertility, <jats:italic>\u03b2<\/jats:italic> = \u22120\u00b7145, <jats:italic>P<\/jats:italic> &lt; 0\u00b7001. Our preliminary results suggest that <jats:italic>Toxoplasma gondii<\/jats:italic> infection could be one of the most important environmental factors influencing the global variation of offspring sex ratio in humans. The effect of latent toxoplasmosis on public health could be much more serious than it is usually supposed to be.<\/jats:p>","DOI":"10.1017\/s0031182016000597","type":"journal-article","created":{"date-parts":[[2016,4,14]],"date-time":"2016-04-14T12:22:06Z","timestamp":1460636526000},"page":"1193-1203","update-policy":"https:\/\/doi.org\/10.1017\/policypage","source":"Crossref","is-referenced-by-count":19,"title":["Do differences in <i>Toxoplasma<\/i> prevalence influence global variation in secondary sex ratio? 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