Men may want to blame biology for their stride, but a new study shows just how literal that excuse is. Researchers at Tel Aviv University (TAU) have discovered that the modern human male pelvis underwent a dramatic evolutionary rewrite, leaving men with a unique hip geometry, while Neanderthals and modern women share an older, ancestral blueprint.
In fact, the modern human male pelvis underwent a dramatic evolutionary rewrite. Prof. Yoel Rak of the anatomy and anthropology department led the team that included researchers from Spain, Haifa’s Technion-Israel Institute of Technology, Ramat Gan’s Bar-Ilan University, and Ono Academic College.
They compared two nearly complete male Neanderthal pelvises – one from Israel’s limestone Kebara Cave situated 60 to 65 meters above sea level on the western escarpment of the Carmel Range in the Ramat Hanadiv preserve of Zichron Ya’acov, and the other from the Sima de los Huesos site in Spain – with dozens of modern human pelvises.
Surprisingly, despite their large size and robust construction, the team said the Neanderthal pelvises resembled those of modern human females in most measurements and proportions rather than those of modern human males.
The team members published their findings in the prestigious Scientific Reports of the Nature group under the title “Neandertal pelvis reveals specialized walking apparatus in human males.”
(Neanderthal spelling with a “th” is derived from “thal,” the old 19th-century German word for “valley.” Neandertal uses the modern German spelling after the 1901 spelling reform. Scientists, style guides, and dictionaries now accept or prefer this simpler spelling.)
“Many of the differences between the Neandertal male pelvis and that of the Homo sapiens male seem to stem from the unusual anterior position of the acetabula (hip joints) in H. sapiens males and the subsequent increase in the horizontal anteroposterior distance between the joint and the line of gravity,” the team wrote.
“We suggest that the forward migration of the hip joints transforms the modern human male pelvis into a shock-absorbing device that cushions the drop of the center of mass with every step and, at the same time, stores potential energy in the flexor muscles of the thigh, causing the pelvis to bounce back.
“Thus, the male hip joints shifted forward to create a unique, built-in ‘spring’ mechanism, transforming the male stride into a highly efficient, energy-storing machine built for long-distance walking.”
The team challenged a decades-old anthropological assumption by revealing that the modern human male pelvis, rather than that of the Neanderthal, is the true evolutionary innovation. They found that Neanderthals and modern human females actually share an ancestral pelvic configuration.
In contrast, the modern male pelvis evolved a distinct geometry that positions the hip joints farther forward.
They noted that the Neanderthal pelvis has long been regarded as an anatomically unusual structure that demanded a functional explanation of its own, but the new findings require a new look at Neanderthal pelvises.
The ancestral configuration may have been kept in Neanderthals and in modern human females while the modern human male pelvis underwent substantial evolutionary modification, giving rise to a distinctive anatomical configuration.
Rak explained in an interview with The Jerusalem Post that during every step of bipedal walking, the body’s center of mass drops downward. This drop traumatizes the joints and requires energy to raise the body again in preparation for the next step.
According to their new model, the distinctive geometry of the male pelvis makes it possible for the thigh muscles to cushion the drop of the body’s center of mass, store potential energy during the step, and then release that energy immediately afterward – effectively “springing” the body upward into the next step.
A natural mechanism that acts as a shock absorber, stores energy, and releases the energy with every step, potentially facilitating long-distance walking in modern human males.
The researchers reached a surprising conclusion: the unusual structure of the pelvis may not be that of the Neanderthal, as has been assumed for decades, but rather that of the modern human male. It reduced energy expenditure, improved walking efficiency, and thereby provided a significant advantage during long-distance travel on foot.
Modern human females show the full range of these modifications. According to the researchers, the constraints imposed by childbirth require a relatively shallow pelvis and a sufficiently wide birth canal. As a result, the female pelvis remains closer to the ancestral configuration – the same general configuration found in male Neanderthals.
Rak stressed that the study’s findings changed how we understand the evolution of the human pelvis. It is not the Neanderthal pelvis that is the anomaly requiring explanation; rather, it is the pelvis of the modern human male.
The researchers note that the study presents a new biomechanical model that may explain a substantial part of the human pelvis’s sexual dimorphism – the anatomical differences between females and males.
Unrecognized structures in human macroscopic anatomy
The research also shows that even in human macroscopic anatomy – the study of the body’s large structures and organs that you can see with the naked eye – which is a field that might appear to have been thoroughly explored, there is still potential to uncover previously unrecognized structures, geometries, and mechanisms of biological significance.
In prehistory, said Rak, “males were hunter-gatherers and walked more than females to find food. Females may also have hunted and collected food, but they did this closer to home and walked shorter distances. If females had adopted the male model, it would have been hard for them to give birth.”
He met “contemporary indigenous Ethiopians who came to see us from 40 kilometers away, and then returned home another 40 kilometers in a single day,” Rak recalled.
Asked about the differences between the bone structure of Neanderthals, who lived primarily in Europe and western Asia, and Denisovans – who roamed mostly across continental and eastern Asia, with fossil and DNA evidence stretching down to Southeast Asia and Oceania, Rak said these were two distinct, extinct groups of archaic humans that branched from a common ancestor around 400,000 years ago.
“But little is known about the skeletons of Denisovans, because the only evidence of their existence was part of a tiny female pinkie finger bone excavated in 2009 in Denisova Cave in the Altai Mountains of Siberia dating back between 50,000 and 80,000 years ago,” he said.
Neanderthals had longer pregnancies than modern females: “Only small hints about the female Neanderthal pelvis exist, and we don’t have a whole one. We can know from the DNA if the skeleton is male or female. We know about modern human skeletons because we have them in museum collections and in medical schools,” he explained.
The team investigated walking and not running, because from anatomy and evolution of humans, they ran only if a large and hungry animal chased them; they would have been the prey. If they wanted to kill an animal, they waited until it stopped, walked slowly, and surprised it.”
Homo sapiens ultimately expanded successfully across large geographic distances, while Neanderthals, whose pelvis was biologically primitive and not developed, did not.
“The skull was different, and they had an advantage in the surroundings where they were raised. But when their home changed, they had a problem. We don’t know if Homo sapiens killed Neanderthals, but they competed in the same environment. They lived together in the same area for 5,000 years,” Rak said.
Prof. Ella Been of Ono Academic College, a co-author of the study, added: “This study shows that questions about human evolution are not confined to the distant past. Understanding the evolution of our walking mechanism can contribute to contemporary research in biomechanics, musculoskeletal medicine, rehabilitation, and injury prevention. The perspective provided by the Neanderthals helps us better understand the modern human body.”
Asked why their research is important, Rak concluded: “Some say the subject has been exhausted, that there is nothing more to discover, but our discovery is new.
“Looking at the biomechanics, it can explain a lot of things about back pain today. It’s important to walk with a straight back, like a clock pendulum. The same shock-absorbing mechanism could have consequences on joints and osteoarthritis, the design of prosthetic hips, rehabilitation programs, and analyzing walking and standing by today’s males and females.”