The Evolution of Childbirth
One of the more beautiful things about human
evolution is that it applies to everyone. I can safely assume without having met you,
that you were indeed born. Human evolution is the story of all of us,
so today I’m going to talk about the very beginning of our own personal stories: Birth. And don’t worry. I’ve watched all the birthing videos so
that you don’t have to. My name is Riley Harnett and this is the HEAP.
There are two things about human childbirth
that seem weird enough to need explanation. First, childbirth is painful and potentially
dangerous. That’s pretty common knowledge. Bu t secondly, human babies are born with
small brains. 30% the size of a fully grown adult. Compare that with a Chimpanzee’s 40% and
it appears that our newborns are born relatively less competent. In 1960 an idea emerged that unified and explained
these two observations . See, it was already well understood at this time that there are
two clear evolutionary trajectories that had occurred in humans. Bigger brains and walking on two legs, or
bipedalism. To walk on two legs efficiently, you need
a pelvis that allows you to, and to have a bigger brain in adulthood, you need a large
enough one at birth. The idea is that the human body had to compromise.
We evolved a pelvis that allowed for a large
enough birth canal but didn’t restrict our ability to walk, and we evolved a less-developed
brain at birth. One that could grow into a fully-sized one,
but at the cost of having more helpless infants. This trade-off is known as the obstetrical
dilemma. Effectively, it states that childbirth is
painful and dangerous because the evolutionary advantages of being a capable biped with a
big brain outweigh the risks, and that our brains at birth are smaller than chimpanzees
because our body had to compromise with a smaller pelvis to give us the best competitive
advantage.
The obstetrical dilemma is an elegant solution
to the problem. It suggests answers to our human uniqueness
by considering how we came to be in a way that anyone can understand. I mean, consider applying it to something
like a Minotaur. Bull head, human body. We can immediately appreciate how impossible
it would be for this sort of creature to exist in real life. No wonder they died out a few thousand years
ago. I’m joking, yeah, I know Minotaurs are mythological. Let me enjoy my ridiculous comparison. Anyway, we have problems with the obstetrical
dilemma. When you look into the assumptions it makes,
it’s not as strong as it seems. For example, would a wider pelvis actually
make walking more difficult or less efficient? We’ve looked at this, and this idea has
received no support . We also have to realize that we’re not the only bipedal ape to have
ever lived. Our own recent evolutionary lineage features
a number of diverse pelvises. These ancestors of ours were capable of walking
and having children too.
Those brain size differences between Chimpanzee
and Human newborns are also something we can investigate. In case you missed it, Newborn brains are
about 30% the size of adult ones. For chimpanzees, it’s 40%. The obstetrical dilemma would say that this
is the result of evolution shortening our time in the womb, otherwise known as gestation
length. Here’s the thing, our adult brains are so
large that the comparison to newborn brains doesn’t make a lot of sense. We have the largest brain per body size of
the all the primates. Comparing ourselves to Chimpanzees doesn’t
necessarily mean our brains at birth are smaller than should be expected when we consider how
much our brains grow in reaching adulthood. If you compare gestation length to the mother’s
body size among primates. Newborns are in the womb for 37 days longer
than expected. Now there’s a reasonable question you might
have here. Why are we making this comparison? What do mothers’ body sizes have to do with
it? A mother’s body size is generally proportional
to the amount of energy it can provide a fetus or fetuses if we’re talking about mammals
that have more than one at a time.
Bigger body, more baby energy. Smaller body, less. So lets look at birth through the lens of
maternal energy, or as I’m going to call it, Mother power. This is what another line of thinking does,
it’s called the energetics of gestation and growth hypothesis. But we’re going to call it the EGG hypothesis. The EGG states that birth in mammals happens
when the fetus needs more energy than the mother can provide it. Since we developed agriculture, our abilities
to consume energetic foods has only increased. And therefore childbirth hurts not because
of the evolutionary competition between the pelvis and brain, but because we’re able
to provide fetuses with more mother power, and therefore more ability to grow in the
womb than could be provided by an animal of our body size in nature. It also helps explain why babies have, well,
baby fat. Wombs today are like luxury hotels, and those
babies get all the energy they can.
So they grow. They grow until they almost reach the pelvic
limit, and that’s when birth happens. If we apply this idea to minotaurs, then maybe,
just maybe they have a shot at having a reasonable pregnancy. Full transparency, I am speculating here. We’re off in the hypothetical abyss and
there’s no going back now. But while the minotaur of Greek myth ate only
human flesh, actual cattle eat grass. So we should be able to agree that a minotaur
wouldn’t have the high calorie, high carb diets us humans have. As a result, we would expect minotaur babies
to be smaller. And we should also expect them to not have
the great brains at birth that we do. Cattle are born nose first, I know, I checked. So they’re kind of streamlined.. okay this
gone too far.
But you get where I’m trying to go. I honestly can’t say that we can exclude
minotaurs from being a viable species based on our understanding of birth. That actually bothers me and if you’re someone
in the know who can bring me back to earth, I’d really appreciate it if you could leave
me a comment below. Personally I think this is a really beautiful
example of the development of science. We thought we had the right idea with the
obstetrical dilemma. It looked good, it’s easy to understand,
but unfortunately it doesn’t hold up to scrutiny very well. Occasionally science is wrong, but it’s
self-correcting, and I hope I’ve left with an example of a self-correction that applies
to how you understand yourself and everyone around you.
If I’ve left you imagining minotaur childbirth
then you have my sincere apologies. I’ve posted social media links in the description
if you’d like to follow me. Otherwise, if you’ve got the time, check
out another video. I promise that this one doesn’t include
minotaurs. Thanks for watching..
