The Evolution of Human Birth


Hey! So, a few weeks ago Bill and Melinda Gates reached out to us about making a collaborative video based on a theme in their annual letter. This is something that they write every year to share their philanthropic goals for the coming months. One of their priorities for 2017 has to do with maternal and infant health. They want to support initiatives that ensure women remain healthy throughout pregnancy and birth and in the first years of their child’s life—we put it in the description so you can go check it out for yourself. The Gates have been a lot of great work to elevate important topics around global health and education and I’m really excited to be working with them on this project, so check it out! So you might remember Dr. Robert Martin, who you’re familiar with from episodes like “Breast Episode Ever” and “Why did King Tut have a flat head?” He’s a biological anthropologist and has spent his career researching various aspects of Hominid evolution. A big part of his work focuses on the physical aspects of human reproduction and childbirth and how trends and practices in childbirth have changed throughout time. They got me thinking of that face that I made in the King Tut video. Before then, I’d never truly realized the logistical constraints of human child birth. I mean you’ve got to navigate this grapefruit sized head and shoulders through an opening of roughly the same size and make a turn to get around the tailbone in the process. When you compare the pelvic size and shape to that of our closest great ape relatives, ours is disproportionately smaller and more obtuse—and that’s because the act of walking permanently upright, known as bipedal locomotion, actually changed the shape of that pelvic opening. This, in addition to human babies having a longer gestation time, overall larger body size, and massive heads, leads to a lot of complications when it comes to human birthing practices. In fact, in a recent blog post, Dr. Martin wrote “astute analysis of brain size and pelvic anatomy and our fossil predecessors have confirmed that birth first began to become challenging when the genus Homo emerged around two million years ago.” This means that women may have
been relying on personal assistants in order to give birth for as long and 2 million years! So I started to wonder how has our inability to give birth easily impacted mortality rates for both mother and child. Save the Children estimates that a million babies die the day they’re born every year. So why does this happen and are things getting any better? Spoiler alert: these things are actually improving and I went to talk to Dr. Martin to get some answers. This is what a baby’s head looks like at birth and that head has to fit through the pelvis. So the baby goes in with his head facing sideways and then when it’s halfway through the pelvis it turns through 90 degrees to point backwards. It all boils down to a difficult passage through the pelvis because of this trade-off between adaptation of the pelvis for upright walking and this big brain. So all of that points to the need for some kind of assistance. We don’t know exactly when, but we can trace this process through the fossil record fairly effectively and my guess is that we started needing midwives about a million years ago, there’s some kind of help.
EG: You mentioned earlier that we have a great record for knowing how, uh, how humans have evolved over time and how the evolution of birthing practices have evolved over time, so you can talk— can you talk a little bit about some of the examples that we have in the fossil record?
RM: So this here is— this is one side of the pelvis of Lucy, the famous Australopithecus from Ethiopia. So if you mirror image the pelvis and put it together, you can work out how big the birth canal was.
EG: Great.
RM: …and we can calculate how big the baby’s head was likely to be. But then, when you get up to Homo erectus, by 1.5 million years ago with early homo, we almost certainly had the beginnings of a difficult birth. They would have had slower births and maybe they already needed midwives at that stage, it’s quite possible. I think midwives have been undervalued. I mean has been a medicalization of birth and a drive towards having births in hospitals. It’s much better for women psychologically, at least, to be working with a midwife than to go into the impersonal environment of a maternity. There was a study in Holland which showed that if you had a midwife in hospital compared to an obstetrician in that same hospital, birth took twice as long with the obstetrician than it did with the midwives. I mean, it’s pretty dramatic evidence to me.
EG: Something like 300,000 women die because of pregnancy-related issues, but most of those are preventable. I mean sometimes you get blockage of the birth canal but a lot of that just has to do an access to basic health care and assistance in the process. It seems pretty logical to think that if you provide more access to healthcare and to nutrition, to decrease the number of children who are dying of malnutrition, then that would be beneficial all around. This is absolutely true. I mean medical science has made huge leaps forward but in industrialized countries we’ve managed to get birth related mortality down, so that we’re talking about a few per hundred thousand, so I mean these are really pretty low levels. But here’s the thing, if you just take industrialized countries where because of hospital services, we’ve managed to reduce mortality and the lowest country on the list for industrialized countries is the United States. How come the richest country in the world has one of the highest levels of mortality around? There was one drastic case which is the state of Texas. In the state of Texas, maternal mortality was actually not rising very much until 2011. And then it doubled.
EG: Wow. RM: It shot up and it stayed at that level ever since. There’s no health-related factor that can explain that and the only explanation I’ve seen is within 2011, a lot of prenatal clinics were closed. And, so I think there is a good possibility that a political decision in the state of Texas has actually doubled the rate of mortality and that stayed.
EG: Wow, so that’s kind of a shocking example of how decreasing the access to healthcare facilities actually exponentially increases the rate of infant mother mortality. Despite those kind of statistics, things are improving globally for, for women and for infant care. I mean especially if you’re looking in the scale of the last hundred years or so, the percentage of children that are dying between ages 0 and 5 had decreased forty percent in the last hundred years. From instances that might look like things might be getting worse but overall things are improving. Oh absolutely, and I, I don’t want to over- exaggerate things over in the United States is last on the [league?] list for industrialized countries which is still pretty low. Medical intervention and monitoring has got the death rate down considerably. It’s quite a bit worse in developing countries and the highest rates are in Africa. Africa has real problems with health provision, I think, and so we can see there the problems you get if you don’t have regular monitoring.
EG: We have the benefit of technology and medical resources that hypothetically could be available to everybody alive today. 122 million children have been able to live thanks to access to healthcare and education. So that, to me, seems like a huge progress. What do you imagine for the future of humanity if everybody could have access to health care, provided that, you know, you have some idea of what our evolutionary trajection [sic] might be.
RM: Yes, the first thing I would say is a key to the improvement you’ve mentioned is prenatal care. That has already reduced the problems enormously and improved the prospects of birth. Unfortunately a lot of people think the easy way out is to have cesarean births because then you don’t have any problem of passing through the pelvis.
EG: Yeah.
RM: That has got out of hand because WHO reckons that the medical reasons you might need to have cesarean every one in ten or one in seven births something like that. In the United States right now one in three births is by cesarean, so it’s, it’s increa—it’s more than tripled in, over the course of 40 years or so. You have full anesthesia for a cesarean and some major operation, and it has all kinds of side- effects. But the example I, I’ve given in my writings is that in bulldogs, dogs with with really wide heads, we’re talking about 85 to 95 percentages cesarean. And if we don’t watch it we’re going to end up like Bulldogs. [laughing]
EG: Wow. Man, I’m just, I’m grateful for mothers everywhere!
[both laughing] This episode of The Brain Scoop is brought to you by Bill and Melinda Gates and the Field Museum in Chicago, Illinois. … it still has brains on it.