The biology of woman in fact holds the key to the story of the
human race. The triumph of evolution occurred in the female body,
in one critical development that secured the future of the species. This
was the biological shift from primate oestrus, when the female comes
on heat, to full human menstruation. Although generally unsung,
indeed unmentioned, female monthly menstruation was the evolutionary adaptation that preserved the human species from extinction and ensured its survival and success.
For female oestrus in the higher primates is a highly inefficient
mechanism. The great female primates, chimpanzees, gorillas and
orangutans, come on heat rarely, and produce one infant every five or
six years. This puts the whole species dangerously at risk of extinction,
and the great apes today survive only in small numbers and in
the most favorable environments. With twelve chances of conceiving
in every year, instead of one every five years, the human female has a
reproductive capacity sixty times higher than that of her primate sisters. Menstruation, not hunting, was the great evolutionary leap forward. It was through a female adaptation, not a male one, that ‘man’ throve, multiplied and conquered the globe.
— Who Cooked the Last Supper by Rosalind Miles (p. 24)