For decades, scientists have used the human pelvis to study a basic question about our evolution: how did our ancestors balance walking upright with giving birth to large-brained babies?
Neanderthal pelvises challenge a long-held idea about childbirth and walking. Credit: Jaroslav A. Polák / Zollikofer et al., Proceedings of the National Academy of Sciences (2026)
A new study of two unusually well-preserved Neanderthal skeletons questions the classic answer. The researchers found close similarities between Neanderthal and modern human female pelvises in areas linked to childbirth. Features tied to walking, by contrast, differed in several key ways.
The findings, published in Proceedings of the National Academy of Sciences, suggest the main evolutionary trade-off was not between childbirth and efficient walking. Instead, the researchers argue, pelvic form was shaped in part by the need to give birth while keeping the pelvic floor stable.
The study focused on two rare fossils. One belonged to a 1.5-year-old Neanderthal child from Dederiyeh Cave in Syria. The other belonged to a young adult female from Sima de las Palomas in Spain. Both had pelvic bones preserved well enough for detailed study.
The team used medical CT scans, digital cleaning methods and 3D reconstruction to study the bones without altering the fossils. They compared the new models with other Neanderthal pelvises, including the Tabun female and Kebara male, as well as scans of modern humans.
The Neanderthal child already showed several traits typical of adult Neanderthals. The hip blades flared outward, while the pelvis was relatively short from front to back compared with its width. This suggests the basic Neanderthal pelvic shape developed early in life.
Virtual reconstruction of Neanderthal pelves. (A) Infant from Dederiyeh Cave (“Dederiyeh 1”). (B) Young adult female from Sima de las Palomas del Cabezo Gordo (“Paloma”). (Scale bar, 5 cm.). Credit: Zollikofer et al., Proceedings of the National Academy of Sciences (2026)
The results also point to a close link between Neanderthal and modern human childbirth. Female Neanderthals had a wider pelvic canal than males, much like modern human females. The shape of regions involved in birth was also highly similar between the two groups.
These similarities suggest Neanderthal women and modern human women likely used broadly similar birth mechanisms. Both groups faced the challenge of delivering babies with relatively large brains through the pelvic canal.
The differences appear elsewhere in the pelvis. Neanderthals had hip joints and muscle attachment patterns suited to a different style of standing and walking. Their pelvises also showed reduced pelvic tilt and less lower-back curvature than modern humans.
These features point to differences in stance and gait rather than a simple trade-off between a wide birth canal and fast, efficient walking.
The finding matters because the so-called Obstetrical Dilemma Hypothesis has shaped research on the human pelvis for decades. The idea holds that evolution had to balance the need for a broad birth canal against a pelvis suited to upright walking.
Some researchers have already questioned this model. Wider hips don’t appear to greatly reduce walking or running performance, raising doubts about whether locomotion was the main limit on pelvic shape.
The new Neanderthal evidence adds a different possibility. A wide birth canal may have placed greater demands on the pelvic floor, which supports internal organs and helps maintain stability.
The fossil record also offers clues about how these body forms changed over time. Older australopithecine and early Homo fossils had broad pelvises with a side-to-side shape closer to Neanderthals. The narrower front-to-back form of modern humans appears to be a later evolutionary change.
Taken together, the results suggest Neanderthals and modern humans followed different paths in shaping the pelvis. Their childbirth-related anatomy stayed surprisingly similar, while their movement-related anatomy took different forms.
The study therefore shifts attention from walking alone to the wider demands placed on the pelvis. For hundreds of thousands of years, childbirth and pelvic floor stability may have been a more important evolutionary conflict than childbirth and locomotion.
Publication: Zollikofer, C. P. E., Ponce de León, M. S., Uriarte, M. H., López, M. V., Ortega, J., Kondo, O., … Walker, M. J. (2026). Insights into Neanderthal development, childbirth, and locomotion from the Palomas and Dederiyeh pelves. Proceedings of the National Academy of Sciences of the United States of America, 123(35), e2535303123. doi:10.1073/pnas.2535303123