Solving the evolutionary puzzle of twinning 11 Jun 2020

Twins have long been a source of fascination in human societies. Mythologies all over the world use twins to convey hidden messages, and literature repeatedly exploits their potential to amuse, or sometimes unnerve, an audience. But from an evolutionary point of view, they’re a puzzle. Twins have much higher mortality rates in early life than children born in single births and also pose a risk to the mother, increasing her likelihood of dying in childbirth. We seem to be a species designed to give birth to one infant at a time, like other large mammals. Why then has natural selection not weeded out the tendency for women to give birth to twins?