Sex ratio is the ratio of males to females in a population. That is, it is the proportion of males in a population. As per Fisher’s principle, this ratio is 1:1 for most sexually reproducing species. The human sex ratio is, for obvious reasons, studied more than the ratio for any other species. It is of major importance to the studies of anthropology and demography. The sex ratio at birth for the world is 107:100. This is because of the higher foetal mortality in females. The sex ratio is 943 in India as per the 2011 census. That is, there are 943 females for every 1000 males. A skewed sex ratio which is not in favour of women is a dangerous sign because it indicates a higher female foetal mortality rate. This is a particular problem in certain states where there is active sex selection by parents and girls are killed even before they are born. Haryana has the lowest sex ratio in India among states at 879 girls for 1000 boys. Decreasing sex ratios pose dangers for the future female population in the country.