Why Humans Give Birth to Helpless Babies
Scientific American Observations: August, 2012 STAFF
Excerpt: Human babies enter the world utterly dependent on caregivers to tend to their every need. Although newborns of other primate species rely on caregivers, too, human infants are especially helpless because their brains are comparatively underdeveloped. Indeed, by one estimation a human fetus would have to undergo a gestation period of 18 to 21 months instead of the usual nine to be born at a neurological and cognitive development stage comparable to that of a chimpanzee newborn. Anthropologists have long thought that the size of the pelvis has limited human gestation length. New research may challenge that view.
Excerpt: That other factor, they contend, is mom’s metabolic rate. “Gestation places a heavy metabolic burden (measured in calories consumed) on the mother,” Dunsworth and her co-authors explain. Data from a wide range of mammals suggest that there is a limit to how large and energetically expensive a fetus can grow before it has to check out of the womb. Once outside of the womb, the baby’s growth slows down to a more sustainable rate for the mother. Building on an idea previously put forth by study co-author Peter T. Ellison of Harvard University known as the metabolic crossover hypothesis, the team proposes that “energetic constraints of both mother and fetus are the primary determinants of gestation length and fetal growth in humans and across mammals.” By nine months or so, the metabolic demands of a human fetus threaten to exceed the mother’s ability to meet both the baby’s energy requirements and her own, so she delivers the baby.
It ought to be pretty obvious that there is a limit to what size fetus a woman can grow. And the costs to her body wreak havoc on her health!
Note: A Common cause of premature birth today is the INABILITY of a specific female to physically carry the fetus to term. _Young age, obesity, poor diet, drugs & alcohol, Lack of muscle development.
“Archaic” humans (pre-agriculture – pre-domestication) may have had more “mature” bodies compared to contemporary “paedogenic” females: much more “exercise”; better nutrition and more “robust” physiology – the healthiest body possible.
Paedogenesis: reproduction by young or larval animals; the animal reaches sexual maturity while remaining otherwise immature.
Paedomorphosis: retention of juvenile characteristics in the adult animal. This includes behavior.
Neoteny: retention of juvenile traits in the adult animal due to some aspect of the physiological (or somatic) development of an animal being slowed or delayed. Neoteny is a factor in paedomorphosis.