This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The most prominent difference between human male and female skeletons is the pelvis, which anthropologists often use to determine the sex of ancient remains. Scientists have long believed the human pelvis evolved mainly as a compromise between walking on two legs and giving birth to large-brained babies.
This idea is known as the Obstetrical Dilemma Hypothesis. In a recent study, a team of researchers digitally reconstructed the pelvises of two exceptionally well-preserved Neanderthal fossil skeletons: a 1.5-year-old infant from Dederiyeh Cave in Syria and a young adult female from Sima de las Palomas in Spain. The team focused on the nearly intact pelvic bones.
Since Neanderthals were our closest extinct relatives and also had large brains, the researchers wanted to see whether the same evolutionary conflict shaped their pelvises. According to findings published in Proceedings of the National Academy of Sciences, Neanderthal and human pelvises look different overall from a young age. Although Neanderthals had wider pelvises overall, the parts of the pelvis used for childbirth were highly similar to those of modern females, indicating a similar style of giving birth.
However, the parts of the pelvis related to movement were quite different between Neanderthals and modern humans, and the nature of these variations suggested that a wider birth canal did not necessarily make walking less efficient. The researchers therefore proposed that the true evolutionary trade-off may not have been between childbirth and locomotion, but rather between childbirth and maintaining pelvic floor stability. The pelvis of a modern human has features optimized for walking upright and standing, as well as for giving birth to babies with large brains and bodies.
This region is also where male-female sexual dimorphism is particularly pronounced in humans, and for a long time, the pattern has been explained through the Obstetrical Dilemma Hypothesis (ODH): a conflict between the need for a wide birth canal and the need for a narrow distance between the femoral head centers (FHC distance) to enable efficient bipedal walking. This idea, however, didn't win everyone over. Some scientists pushed back, pointing out that wider hips don't actually seem to slow us down when we walk or run, while others suggested the real limiting factor isn't locomotion at all.
It might be the mother's metabolism or the need for a strong pelvic floor to support our internal organs. Fossil pelvises are rare and often fragmented, leaving us with limited insight into how Neanderthals gave birth and moved. Earlier reconstructions of their birth canals only deepened the uncertainty, producing conflicting conclusions.
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