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Sex ratio

Ratio of males to females in a population / From Wikipedia, the free encyclopedia

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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.[2][3] However, many species deviate from an even sex ratio, either periodically or permanently. Examples include parthenogenic species, periodically mating organisms such as aphids, some eusocial wasps, bees, ants, and termites.[4]

Map indicating the human sex ratio by country.[1]
  Countries with more males than females.
  Countries with the same number of males and females (accounting that the ratio has 3 significant figures, i.e., 1.00 males to 1.00 females).
  Countries with more females than males.
  No data

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[5] and by sex-selective abortion and infanticide. Exposure to pesticides and other environmental contaminants may be a significant contributing factor as well.[6] As of 2014, the global sex ratio at birth is estimated at 107 boys to 100 girls (1,000 boys per 934 girls).[7].