# The Pelvic Problem: How Neanderthal Hips Challenge Why We Think Childbirth is so Difficult

*Virtual reconstructions of Neanderthal pelvises suggest birth canal size was a compromise between delivering big-headed babies and keeping the pelvic floor stable*

By Sandee Oster · Published 31 August 2026

Source: https://archaeologyteahouse.com/stories/the-pelvic-problem-how-neanderthal-hips-challenge-why-we-think-childbirth-is-so-difficult

Primary source: [nsights into Neanderthal development, childbirth, and locomotion from the Palomas and Dederiyeh pelves](https://doi.org/10.1073/pnas.2535303123)

Subjects: [Neanderthal](https://www.wikidata.org/entity/Q40171), [Childbirth](https://www.wikidata.org/entity/Q34581)

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![pnas.2535303123fig01](https://archaeologyteahouse.com/media/01a03e37-0b8d-71ad-a870-83743ea18790/1600.webp)

*Virtual reconstructions of an adult female Neanderthal from Sima de las Palomas del Cabezo Gordo. Credit: [Zollikofer et al. 2026](https://www.pnas.org/doi/10.1073/pnas.2535303123#supplementary-materials)*

Why is human childbirth so difficult? It is a question people have been asking for millennia; some of the oldest explanations are biblical: Eve ate the forbidden fruit and got herself, and Adam, kicked out of Eden. One of the punishments for this sin was difficult childbirth.

Okay, and what about the biological reason? I've wondered the same; having seen goats and (at least in documentaries), even elephants give birth, it seems birthing is barely an inconvenience.

In school, we were taught the prevailing theory: walking upright led to difficult childbirths, a simple explanation good enough for high school biology. But the exact science is more complicated and has been debated for decades. The most common theory holds that the human pelvis evolved through an evolutionary tug-of-war called the 'obstetrical dilemma.' The pelvis needed to be wide enough to allow for the birth of big-headed babies, but narrow enough to walk efficiently. Nice theory, but how do you test it?

Compare our pelvis to another species that had big-headed babies and habitually walked upright, and that's what a recent study by Christoph Zollikofer and his colleagues published in *PNAS *did.

They found that the parts of the pelvis involved in childbirth were similar in modern humans and Neanderthals; what differed were the parts involved in walking. The mismatch suggests perhaps the real evolutionary tug-of-war wasn't between walking and childbirth. They suggest the real compromise may have been between childbirth and our pelvic floor.

### An Evolutionary Tug-of-War

![Untitled design(7)](https://archaeologyteahouse.com/media/01a03e46-acd0-70bf-8f82-cac64a545fab/960.webp)

*Neanderthal mother with her child in the Anthropos Pavilion of the Moravian Museum. Credit: [Wikimedia Commons](<https://en.wikipedia.org/wiki/Neanderthal#/media/File:Brno,_Neanderthal_Mother_(detail_of_diorama).jpg>)*

Before I get into the results let's recap the obstetrical dilemma, first coined in the 1960s the idea is basically that a wider birth canal is great for delivering large headed big-brained babies, but the wider the birth canal the less efficient walking becomes, so it turns into a balancing act: a pelvis just wide enough to deliver a child safely, but narrow enough that we can actually walk.

The idea has both its supporters and detractors. Some say a mother's metabolism (energy expenditure) is what really limits the length of pregnancy. Others point out that women with particularly wide hips don't have any more difficulty walking than any other woman. Others argue the real limiting factor is the pelvis's ability to support the pelvic floor (the sling of muscles that keep our organs in place). Others hold a 'multifactor' view, aka the pelvis balances the need to fit a baby through the birth canal, with efficient walking, pelvic floor stability and even heat regulation.

To test these theories, we need something to compare against, but not every bipedal animal is suitable. Ostriches walk upright, but lay eggs; kangaroos are mammals, but they give birth to (essentially) a fetus, so we look to primates. But chimps, gorillas, and orangutans have their own problems: they are not fully bipedal.

Our ancient ancestors, the Australopithecines, walked upright, but working out how they gave birth is difficult. Their babies are thought not to have turned while giving birth like ours do. This rotational birth seems to have evolved later, possibly tied to a narrower pelvis better suited for long-distance running.

That's where Neanderthals come in; they are our closest extinct relatives, walked upright, gave birth to big-headed babies, but their pelvises retain the old evolutionary shape, making them a perfect point of comparison.

Unfortunately, few Neanderthal pelvises survive. The pelvis is fragile and tends to shatter into pieces over time. When I come across pieces of the pelvis in archaeological assemblages only a few thousand years old, what remains is often just a small fragment of the hip socket. Now imagine a Neanderthal pelvis tens of thousands of years old; it is unlikely to survive.

When they are found, they are often fragmented into dozens of pieces and crushed by sediment, leaving many questions about their shape, size, and evolution.

Various reconstructions have reached different conclusions about Neanderthal birth. What also remains unclear is how male and female Neanderthal pelvises differed: whether they were like ours, or whether the differences were more subtle, as in modern primates, and how those differences arose.

To answer these questions, Zollikofer and his team digitally reconstructed the 2 best-preserved Neanderthal pelvises ever found: one from an 18-month-old infant at Dederiyeh Cave in Syria, the other from a young adult female at Sima de las Palomas del Cabezo Gordo in Spain.

They compared these two with the only other nearly complete Neanderthal pelvises (one male and one female), as well as 146 modern human pelvises.

### Making a 3D Pelvis

![Untitled design(6)](https://archaeologyteahouse.com/media/01a03e3b-83e3-73b4-92c2-55d9588e1908/960.webp)

*Virtual reconstruction of the in-situ 'Paloma' pelvis. Credit: [Zollikofer et al. 2026](https://www.pnas.org/doi/10.1073/pnas.2535303123#supplementary-materials)*

The Dederiyeh infant was well preserved, but because it was so young, its bones had not fully fused. Using CT scans of modern infants, the researchers determined how much cartilage would have sat between the bones and virtually pieced them back together.

The Palomas adult had been crushed and was partially still within the rock. The researchers CT scanned the specimen, digitally removed it from the surrounding sediment, reassembled the fragments, and created a mirrored copy of missing pieces (so if one fragment survived on the left, it was reflected on the right).

Each adult fossil was reconstructed in three ways to allow for uncertainty, then compared. The baby Neanderthal was compared against 34 modern children aged between 1 month and 8.4 years. The adult female Neanderthal pelvis was compared with 112 modern male and female pelvic specimens.

The infant results showed that it sat at the upper end of the normal human range but already had the distinct Neanderthal shape, including flared hips, a less tilted sacrum (the shield-shaped bone at the base of the spine), and a wide side-to-side but short front-to-back shape.

For adults, age and size barely mattered, whereas differences between the two species and between the sexes were more pronounced.

Neanderthals had flared hips, short front-to-back and wide side-to-side pelvises with hip sockets placed further back and facing more backwards, while longer pubic bones at the front made up the difference.

Most importantly, Neanderthal sex differences matched ours, with females having a wider, shallower lower pelvic region, shorter hip bones, a sacrum sitting farther back, and hip sockets angled more forward, all features that facilitate childbirth.

In modern females, the shape of the birth canal (how oval, front-to-back or side-to-side) varied enormously between individuals, but in terms of size, women typically had much larger canals than men.

So, do the results tell us whether walking efficiency affects how easy or difficult childbirth was, just as the obstetrical dilemma proposes?

### Walking vs Childbirth

![pnas.2535303123fig03](https://archaeologyteahouse.com/media/01a03e48-7cfe-7062-926e-5cd4273e8c24/960.webp)

*The main ways pelvic shape varies: between Neanderthals and humans as infants (A) and adults (B), between the sexes (C), and between individuals of the same sex (D). Credit:[ Zollikofer et al. 2026](https://www.pnas.org/doi/10.1073/pnas.2535303123#supplementary-materials)*

The Dederiyeh baby played an important role because it showed characteristic Neanderthal-style hips at a young age; this suggests the shape was set very early, during growth in the womb rather than developing late in life due to lifestyle.

Both Neanderthals and modern humans exhibited the same sex differences, with females having wider birth canals than males, reflecting the shared burden of childbirth.

What's interesting, though, is what *doesn't* differ. The entrance proportions are the same in men and women, so the shape of the canal's opening likely wasn't shaped by selection for childbirth. That undercuts a theory from the 1930s blaming pelvis shape for difficult births.

Real deliveries, it seems, are harder or easier for reasons beyond bone shape: whether the baby is facing forward or backwards, for instance, which a fossil can't tell you.

What's more interesting: Neanderthal and human pelvis bones related to walking were different. If birth was difficult because both species needed to walk efficiently, both should have similar walking mechanisms. While Neanderthal pelvises favored a stable trunk and strong strides, ours evolved to be better at long-distance running.

If the birth canal isn't shaped by walking, what is? The answer may be the pelvic floor.

A large birth canal means a wider gap that the pelvic floor muscles have to span. It's fighting to keep your organs in; the wider the canal, the more it has to work, but making the birth canal too small means you can't deliver a baby (at least not safely), so the evolutionary tug-of-war may have been between a birth canal narrow enough to support the pelvic floor but wide enough to deliver a big-headed baby.

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So childbirth is difficult, but perhaps not for the reason many of us have long believed. Yes, walking *upright* is still ultimately involved; a pelvic floor only has to hold everything up the way it does because we are bipedal, but the trade-off isn't about walking *efficiently*. Zollikofer and his team concluded that the evolutionary trade-off may have been about giving birth to a large-headed baby while keeping the pelvic floor able to hold everything else in.

The study does more than reconstruct two broken pelvises; it gives us the first real chance to test a 60-year-old theory against a species other than our own, and provides crucial insights into how one of our closest relatives gave birth and since we now know the two species interbred, it tells us those hybrid babies were born much the way ours are, with mothers from both species likely facing the same painful problems.

So maybe we shouldn't be too harsh on poor Eve; we modern humans would have had a hard time giving birth regardless of her decisions. Also, there are animals that have it far worse than we do. Don't believe me? Kiwi lay eggs that occupy around 25% of the mother's body, and spotted hyenas give birth through a pseudo-penis...and neither of those animals did anything dubious (that we know of)  in the Garden of Eden. 

What are the factors you think make human childbirth particularly difficult, and do you think the size of the birth canal is a tug-of-war between the pelvic floor and big-headed babies, or is something else at play?

*Let me know what you think, and if you'd like to support this blog and the person writing it, you can *[*chip in once, monthly, or yearly.*](https://archaeologyteahouse.com/support)* Only if you'd like to.*

### Reference

C.P.E. Zollikofer, M.S. Ponce de León, M.H. Uriarte, M.V. López, J. Ortega, O. Kondo, T. Akazawa, & M.J. Walker (2026). Insights into Neanderthal development, childbirth, and locomotion from the Palomas and Dederiyeh pelves, Proc. Natl. Acad. Sci. U.S.A. 123 (35) e2535303123, [https://doi.org/10.1073/pnas.2535303123](https://doi.org/10.1073/pnas.2535303123)