Anthropology / Everything Human

Labor Pains and Helpless Infants: Eve or Evolution? (Part 2)


Labor Pains and Helpless Infants: Eve or Evolution? (Part 2)

In Part 1 of this post, we discussed two explanations for difficult childbirth and helpless babies: the Fall and the obstetrical dilemma (OD) hypothesis. Both have their weaknesses. Let’s consider another evolutionary-minded explanation, apart from the OD.

For humans, the birth process begins at the same time that pregnancy reaches a critical metabolic threshold. This suggests there is a connection between the two. As a fetus develops and demands more and more from its mother, her body approaches a physiological limit that triggers birth. (Although lactation is also demanding on her body, the mother never surpasses this limit after birth.) This concept has long been described by Peter Ellison’s metabolic crossover hypothesis. My colleagues (including Ellison) and I extended this thinking about a pregnant mother’s metabolic limits to the species level—and to other mammals—in the form of the EGG (energetics of gestation and fetal growth) hypothesis.

Even though constraints remain the leading role in this story, we’re talking about a woman’s metabolic and energetic ceiling, not her pelvic passage (or her moral fiber). This isn’t to ignore the fact that the birth canal is a very real upper limit on fetal size! Of course it is, but it’s not necessarily a uniquely human one, let alone for uniquely human reasons to do with bipedal walking and running, as the OD has it.


The timing of human birth may be less exceptional—and more like that of other species, like these long-tailed macaques—than the OD hypothesis would have us believe. Steve Childs/Flickr

As you might expect, the EGG hypothesis has met with some energetic resistance. One common response is that the tight fit at birth between mother’s pelvis and baby’s head is too much of a coincidence to ignore. But other primates, such as macaque and marmoset monkeys, as well as other mammals, have tight fits too. What explains their tight fits at birth? And could those explanations apply to humans? Those questions reflect the spirit of the EGG hypothesis. Additionally, it’s possible that the accelerated metabolism of Homo sapiens, compared to that of other apes, allows pregnant mothers to grow such large babies with such big, metabolically expensive brains.

Another common question I hear in reaction to the EGG hypothesis is, why doesn’t the birth canal get bigger to make childbirth easier? This question, to me, is not a question. Clearly it’s good enough: Billions and billions of humans are evidence of this. It’s possible that childbirth was never as difficult for hominins as it has been for humans since the dawn of agriculture. For many of us in recent history, agriculture has lowered our disease burden and increased our long- and short-term caloric intake, all contributing to our ability to grow big maternal bodies that are metabolically capable of growing big fetuses inside of them, especially in a calorie-rich environment. This could at least partially explain the increase in newborn size over the last few decades reported by U.S. and European hospitals.

However, agriculture has not been paradise for everyone. It has caused an increase in infectious and nutritionally based diseases, and caloric deficits as well. Future mothers who are developing during those terrible circumstances may experience stunted growth, including that of their birth canals. Fetuses and their placental partners are very good at growing up large despite mothers’ conditions, creating potential for a very tight fit at birth, or worse.

Larger babies are associated with longer labors and higher incidences of medical interventions. And this phenomenon has borne out two simultaneous but opposite truths: First, medicine has helped solve some of this evolutionarily recent dilemma, which has been intensified by agriculture. But second, medicine has also helped make childbirth more difficult now than ever before. That is, the direct and indirect fallout from medicalizing childbirth has routinely but unnecessarily complicated successful childbirth. OD-style thinking that medical intervention in childbirth is an “evolutionary imperative” has helped exacerbate this situation, which is much more cultural than evolutionary.

Like obstetrical medicine, the idea of the “obstetrical dilemma” has been a blessing and a curse. It’s been a blessing because it provided a plausible evolutionary explanation for something that we’d long blamed on Eve.

But it’s been a curse too, because it’s so elegant that it has encouraged us to hang on to old anthropocentric and sexist assumptions. It has blinded us to alternative points of view, like EGG thinking. And it’s been used to justify unnecessary obstetrical intervention.

Like obstetrical medicine, the idea of the “obstetrical dilemma” has been a blessing and a curse.

The OD is even such a good evolutionary tale that, in comparison, a friend of mine called the EGG hypothesis unevolutionary—presumably because it’s less about adaptive tradeoffs and human exceptionalism and more about humans working with limited energy budgets and finite metabolic capacities, just like any other primate or any other mammal. But if the EGG hypothesis—a biologically based explanation for the timing of human birth—isn’t about evolution, then what is it about? It’s definitely not about Eve.

Still, Eve’s story sits front and center of the most-read book in history. And no matter what one thinks about its accuracy, it gives certain aspects of the human condition the attention they deserve. Childbirth’s difficulty and the risks to the lives and health of mothers and infants are common to all societies. Inequality increases these risks. Economic, health care, educational, and nutritional inequality contribute to pregnancy- and childbirth-related trauma and mortality all over the world. Gender inequality’s to blame too, and it compounds the other issues. Ironically, Eve’s story does little but encourage us to accept all of this as natural.

Shifting the narrative away from punishment opens up an opportunity for celebration. Imagine all the women who gave birth to big, fat, brainy babies after a relatively long (did I say long?) pregnancy! Imagine all the women who then raised those nongrasping, wobbly-headed, puny-bodied babies despite the years (did I say years?) it takes these particular primates to grow into self-sufficient humans. These women may have only metaphorically kept the world turning, but they’ve literally kept families, lineages, species, and, yes, evolution going. It doesn’t take an evolutionary perspective to see this profoundly beautiful and simple reality, but it helps.


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  • Melanie Fraser

    Do you think there’s mileage in the squat/toilet theory? As in, if we were used to squatting to excrete several times a day, and otherwise fit as well, we’d find childbirth easier?

    • Holly Dunsworth

      I don’t know anything about it. All I know is the current state of comparative knowledge and it’s that humans as a species, including the large numbers of us who are squatting regularly during the day for many reasons (not just to void), have a difficult time with birth compared to nonhuman primates.

      • Melanie Fraser

        I understood the theory as follows: (1) prior to modern sit-toilets, human females would squat to toilet many times a day; (2) this developed their squatting abilities and muscle strength, as well as generally being pretty strong and fit; (3) squatting to toilet also increases the woman’s understanding of how to use her pelvic floor and control the musculature generally in the area (4) squatting to toilet increased in frequency during pregnancy (5) giving birth in a squat position is one of the best physiological stances, especially if combined with good pelvic floor control (6) childbirth in squat-toilet contexts is therefore easier. (6) the absence of squat toilets means that it’s hard to give birth in a squat position.

        • Holly Dunsworth

          I understand. What I meant was that, unfortunately, I don’t know anything about evidence for it. Remember, too, that many if not most women on the planet today do not have seat-style toilets in their lives.

        • Holly Dunsworth


  • Holly Dunsworth

    Here is a very informative post called “What is the Evidence for Induction or C-section for a Big Baby?”

  • joseph2237

    It is totally clear that our species shouldn’t have been any success at all considering the helplessness of the mother and child after delivery. It is a marvel and a wonder of nature that such a lame birthing method should give rise to the dominate species on the planet. Most successful species have multiple babies not just one and all begin working almost immediately. One reason for the single offspring is our children are well protect and have few predators, but one child is never the less risky

    • Hans Dunkelberg

      I’m not sure if we are “the dominate species on the planet”, but the problems connected with the way human babies are born will not have given rise to our success. These problems rather Some of these problems (in particular, the helplessness of the baby, usually ascribed to the unusual size of its head, which would be responsible for especially early births of our infants) rather might be a byproduct of a strategy that has us beginning to mold practical intelligence into evolving brains, at an especially early stage of the infantile development. You can’t teach an old dog new tricks!

      [I have edited the beginning of the second sentence, after two days.]

      • Holly Dunsworth

        We are not born early. If anything, we’re born after a longer than predicted gestation for primate of our size. We are born with absolutely larger brains/heads than any other primate. If one must choose between the two, we are born advanced, not immature or early.

        • Hans Dunkelberg

          The phrase “If one must choose between the two” (concerning the question if we are born advanced or immature / early) leaves a large room for interpretation. You apparently mean that human infants are more advanced than the ones of other species because their conspecifics guarantee an according advantage. That human babies cannot even see properly, in the beginning, to say nothing of walking, may appear as insignificant, from such a point of view.

          A thing I would like to add is that any difficulty will provoke an upsurge of intellectual zeal and of cooperation, among the grown-ups. And out of an interest in the welfare of infants one should also note in what a way dangers around newborns can have had a function of a selection procedure, concerning the children, themselves. Just like an employer wants applicants to demonstrate certain abilities, a survival formula of our ancestors probably has included comparable tests, especially in the first months and years of an individual’s life. Nowadays, when there have emerged according possibilities, this constellation will have one advocating a very conscientious handling of children!