Modern Human Male Pelvis May Be an Evolutionary Innovation
A new Tel Aviv University study suggests that the modern human male pelvis evolved as a biomechanical system that may improve walking efficiency over long distances.
A new study from the Department of Anatomy and Anthropology at Tel Aviv University offers a new explanation for one of the striking anatomical differences between men and women: the evolution of the modern human pelvis.
By comparing Neandertal pelvises with those of modern humans, the researchers reached a surprising conclusion. Rather than the Neandertal pelvis being the anatomical anomaly, as has long been assumed, the pelvis of the modern human male may represent the evolutionary innovation.
The study, led by Prof. Yoel Rak of the Department of Anatomy and Anthropology at Tel Aviv University and conducted in collaboration with researchers from Spain, the Technion, Bar-Ilan University, and Ono Academic College, was published in Scientific Reports.
The researchers compared two nearly complete male Neandertal pelvises—one from Kebara Cave in Israel and another from the Sima de los Huesos site in Spain—with dozens of modern human pelvises. Despite their large size and robust structure, the Neandertal pelvises resembled those of modern human females in most measurements and proportions more closely than those of modern human males.
A Different Way to Look at the Human Pelvis
The central finding is that the hip joints of modern human males are positioned farther forward on the pelvic ring than those of both modern human females and male Neandertals.
According to the researchers' biomechanical model, this configuration creates a system in which the anterior thigh muscles function much like a spring. During walking, as the body's center of mass moves downward, the muscles can help cushion the movement, store potential energy, and then release it as the body rises into the next step.
In this way, the male pelvis may function as a natural shock absorber and energy-return system, potentially reducing energy expenditure and improving the efficiency of long-distance walking. The shift in the position of the hip joints was accompanied by other structural adaptations, including thickening of the pubic bone and deepening of the anterior portion of the pelvis to withstand the altered mechanical loads.
Why Are Female Pelvises Different?
According to the researchers, modern human females could not adopt the full set of these anatomical modifications because of the constraints associated with childbirth, which require a relatively shallow pelvis and a sufficiently wide birth canal. The female pelvis therefore remains closer to the ancestral configuration also observed in male Neandertals.
Prof. Ella Been of Ono Academic College, a co-author of the study, notes that understanding the evolution of human walking may also contribute to current research in biomechanics, musculoskeletal medicine, rehabilitation, and injury prevention.
Prof. Rak emphasizes that the findings shift the perspective on pelvic evolution: rather than viewing the Neandertal pelvis as the structure requiring explanation, the study suggests that the distinctive pelvis of the modern human male represents the evolutionary innovation.
The researchers note that the proposed biomechanical model may explain a substantial part of the sexual dimorphism of the human pelvis and demonstrates that even in macroscopic human anatomy, previously unrecognized structures and mechanisms of biological significance may still be discovered.
The study was published in Scientific Reports.
