Eve: How the Female Body Drove 200 Million Years of Human Evolution

Bohannon describes the ecological apocalypse, Chicxulub, that occurred about 66 million years ago, likely following an asteroid, in which nearly all the creatures except the small ones died. One such survivor was a rat-like creature called Protungulatum donnae, or “Donna,” who gave female humans the evolutionary trait of the placenta. Though Morgie and her near descendants laid eggs, before Chicxulub, her descendants started growing their babies inside their bodies, becoming either marsupials, which have pouches, or eutherians, which have a placenta (73). Bohannon explains that despite the taxing and dangerous nature of pregnancy and childbirth, pregnancy regulates the embryo’s temperature, keeps it safe from predators, and allows the mother to look farther for food. She then says that the uterus, ovaries, and fallopian tubes are remnants from when mammals used to lay eggs. The evolution of the placenta started following Morgie’s time with the development of monotremes, which have a single cloaca; marsupials, which have two holes; and placentals, which have three holes. Placentals needed to evolve to protect their babies from bacteria, with monotremes like the platypus producing eggs with an anti-bacterial fold in their cloaca. However, eggs can still be exposed to urinary and fecal germs when they are laid.