ACTUALLY. I study what you might call maternal-infant evolution and pediatric anthropology…I dunno, it’s such a new and small field that it doesn’t really have an official name. Basically, I study mothers and infants as a unit (“dyad”) that co-evolved — sometimes cooperating, sometimes competing.
Anyway, you’re both kind of right but also a little off in some parts. But the first thing that should be acknowledged is that we don’t know for sure why babies are born when they’re born. It’s a HUGE mystery that we’re not even close to solving.
Yes, babies’ heads mold, a LOT:
The skull bones literally slide over each other like tectonic plates in order to lessen the circumference. However, the molding is limited, and birth is still very, very painful for some women.
Also,
the pelvis literally comes apart in three places
muscles, tendons, and skin stretches
and the vagina unfolds (unfolds, not stretches, like an accordion).
These processes, too, are limited. Women also vary in their degree of flexibility, their individual anatomy, etc.
callstheadventurescience is on the right track with energetics…
The foundation for the idea that human infants are born too early is based on the most prevailing theory on the timing of birth, called the “obstetrical dilemma.” The name implies that it was a “problem” that was encountered by evolution at some specific point in time, but it is really just a way of thinking of the competing forces of encephalization (our brains getting bigger over the generations) and our advancing bipedalism.
(L to R: "Pan" = chimpanzee; "AL 288-1" is Australopithecus afarensis, aka "Lucy," which lived from 3-4 million years ago; humans, a.k.a. your mom. Go call her.)
However, the obstetrical dilemma failed to explain the actual mechanism that triggers birth. Also, there have been studies that contradicted one of the foundational assumptions of the theory, which is that a narrower pelvis is more efficient for bipedalism and therefore would be favored by natural selection.
Thus, around 2012, the energetics/life history theory camp came up with the hypothesis that is more of a cost-benefit dilemma. I won’t get into specifics, but the basic idea is that there is a limit on the amount of calories that a mother can “afford” to contribute to a fetus before the process starts to become inefficient. And we all know that crucial evolutionary processes like reproduction don’t tolerate inefficiency well. Therefore, they say, the fetus is ejected when it begins to starve.
That having been said, yes, our infants can live on their own on the outside world — but not as well as we like to think. Our resource-rich society and our independence-oriented Western parenting style might make us think so. But the processes that determined when babies are born happened in an environment where resources were scarce.
To get to the heart of this evolutionary mismatch situation, we need to start with cross-species comparisons. In the mammalian world, we have "altricial" and "precocial" babies. The altricial ones include most rodents — they’re born almost completely helpless. Eyes closed, can’t move, can’t run from danger, etc. On the other end of the spectrum is precocial mammals. They tend to be the larger ones and have longer gestational periods, like horses, elephants, giraffes. Giraffes are up and running within 10 minutes. They need to be, because many of them are prey.
vs:
(<10min old, still wet from amniotic fluid)
Judging by the size of our babies, relative to the size of our mothers, you’d expect humans to be precocial, like other large mammals.However, human babies are in a weird category we call “secondary altricial.” The size of the infant at birth relative to its mother suggests that we should be precocial. However, we cannot move around, let alone run from predators. We cannot even walk to the breast to nurse. Hearing is muffled, and eyesight is good enough only so that we can see from our mother’s breast to her eyes.
More recent research, conducted over 30 years by an old professor of mine as well as others, has started to paint a picture that suggests to us that human infants are born, shall we say, mostly — but not fully — “cooked.” And while it isn’t quite the same as a kangaroo or koala, it does require our physical assistance in their continued development that goes beyond mere nutrition. It has been casually called it the "fourth trimester." In academic papers, I have read the term "exterogestation."
This research has mostly involved monitoring physiological processes of breastfeeding dyads while cosleeping. Why breastfeeding? Because breastfeeding causes hormonal and neurological changes in the mother that the researchers believed, and have shown, are adaptive (and protective). A breastfeeding mother’s neurological physiology is, simply put, markedly different from a non-breastfeeding mom’s, and more closely resembles evolutionary conditions. Measurements included EEGs (aka “brainwaves”), EKGs (heart rate), breathing, CO2 exchange, and behavioral observation using an infrared camera. What they found was, the mother and baby’s breathing, heart rate, and sleep patterns synchronized. The belief is that this synchrony, coupled with the highly stimulating presence of the mother, "trains" the infant’s still-maturing nervous system until such point that it can function on it’s own.
This constant physical proximity requirement that human infants seem to need is supported by their inability to regulate their temperature on their own until a certain age. The closeness of the mother allows the infant to devote more energy to the rapid brain growth that is occurring. Without enough contact, the infant may stop developing and be diagnosed with something called “failure to thrive, the criteria for which includes, among other things, cessation in weight gain, and a sad sort of listlessness or lack of interest in their surroundings.
The need for proximity is also supported by the fact that the ratio of fat-to-calories in our milk is more representative of “carry” species, which are species carry their young around with them all day and night, than it is of “cache” species, such as deer, which stash their babies in a thicket while they go off for hours searching for food. A baby deer has a crapton of fat in their milk to sustain them for long periods of time. Our milk has a much lower fat content, which suggests that we are not meant to leave our babies for very long periods of time.
Another consideration is simply a practical one: in the environment in which this physiology was shaped, we weren’t at the top of the food chain. Being left alone, for a human infant, was dangerous. (In my undergrad lab we had a replica of a skull of a 3 year old australopithecus that had holes in it from being carried off by a freaking BIRD.)
…Thus, our babies can be thought to be more dependent on us than the young of precocial animals like deer and elephants.
Also supportive of this neurological immaturity, is recent research that supports the idea that the cause of SIDS has to do with brain abnormalities in the brain stem — where alertness is regulated. In a safe breastfeeding-cosleeping situation, infants are kept from falling into too deep of a sleep….You see, the phrase “sleep like a baby” is misleading, because babies aren’t supposed to sleep deeply. Their brains might not be mature enough to rouse them when they have an apnea (it is normal for adults and children to stop breathing momentarily several times throughout the night). In these breastfeeding-coseeping pairs that my professor studies, he has seen a mother wake from the deepest stage of sleep, RIGHT at the moment when her baby has an apnea. We know that premature infants, as well as infants whose mothers smoke, have a higher risk of SIDS. It is thought that physical proximity + breastfeeding can help protect those infants who did not quite finish cooking. It is useful to recommend breastfeeding and cosleeping to everyone, since we don’t yet have a surefire means of predicting which infants will be born with this abnormality.
Thus, it is thought, the human infant, it appears, can be thought to have been born “too early.” Or at least that it is not a completely independent organism yet.
This issue is certainly not cut-and-dry. There is a lot of grey area. This idea of the immature human newborn is mostly useful insofar as it helps parents to understand why their babies seem to scream every time they attempt to lay them down in their crib or, for some babies, when they try to set them down at all. Being alone, in their little cavebaby brain, means death. This kind of stress can cause the infant’s adrenal glands to start pumping out stress hormones, including cortisol, which inhibits digestion and growth. One anthropologist in my field says that when a human infant cries, “its nervous system is signaling life-threatening danger.”
Probably more of an explanation than anybody wanted, but I hope at least some of you find it interesting. I think it’s freaking awesome. But of course, it’s what I do lol.
jbbartram-illu
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romaincrisis
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