Humans, like the other Great Apes, are physiologically riders; breast milk composition is not suited to parking infants for long periods between feeding (Ross). For this reason among many others, our species has had to carry our babies with us wherever we go. Unfortunately, humans find carrying infants more difficult than our evolutionary cousins for three reasons: lack non-grasping feet and body hair, physically helpless infants and, most importantly for this post, the relative size of our infants.
Non-human apes in the taxonomic family Hominidae (literally means “Great Ape” and makes me think of Charlotte’s Web’s “Some Pig” but I digress) have smaller, more precocious babies than humans. Adult gorillas, for example, are significantly larger than adult humans, yet their newborns are about half the size of human newborns. Chimpanzees, which are our closest extant evolutionary relative and have a similar adult body weight to us, give birth to newborns that are around 3% of their adult size, while humans have newborns that are around 6% of adult size (DeSilva). At what point since our common ancestor with chimpanzees, did hominins start having bigger babies? Continue reading