Humans, like all primates, are physiologically riders. Riders carry their young because their breast milk composition is not suited to parking infants for long periods (Ross). Nonhuman primates can carry their babies without the aid of a tool because their infants are small and able to cling to their mothers from birth. Humans find carrying infants more difficult for three reasons: the relative size of our infants, non-grasping feet, and lack of adult body hair. In this post, we will focus on how the differences between primate and hominin feet, how feet affect carrying, and when bipedalism emerged.
“Birthing larger infants… also introduces the energetic and biomechanical challenge of transporting a relatively large, helpless newborn. This is particularly the case for pretechnological, upright walking hominids, some of which had reduced pedal grasping abilities.” (DeSilva)
Humans are altricial, our infants are relatively helpless. Nonhuman primates are precocious, meaning that they have accelerated physical development. Both human and ape newborns instinctively grasp with hands and feet. When a chimpanzee is born, they are able to grasp their mother’s fur with their hands and feet and cling on effectively. Whereas a human newborn is not as strong or directed in their efforts though they can strongly grasp with their hands (palmar grasp reflex), they can only flex their toes (plantar reflex) due to the morphology, or shape, of their feet which lack an opposable hallux (a big toe that looks more like a thumb). In humans, this grasping instinct is considered part of the primitive reflexes, which fade as humans develop.