The
sex ratio is the
ratio of
males to
females in a
population. In most sexually reproducing species, the ratio tends to be close to 1:1. Reasons for the tendency are discussed in
Fisher's principle. For various reasons however many species deviate from anything like an even sex ratio, either periodically or permanently. Examples include parthenogenic species, periodically mating organisms such as aphids, some
eusocial wasps such as
Polistes fuscatus and
Polistes exclamans, bees, ants, and termites.