The evolution of human skull took place along with two-legged walking, researchers have confirmed.
Compared with other primates, the large hole at the base of the human skull where the spinal cord passes through, known as the foramen magnum, is shifted forward.
While many scientists generally attribute this shift to the evolution of bipedalism and the need to balance the head directly atop the spine, others have disagreed with the suggestion of the link.
However, the new study published in the Journal of Human Evolution, showed that a forward-shifted foramen magnum is found not just in humans and their bipedal fossil relatives, but is a shared feature of bipedal mammals more generally.
"This question of how bipedalism influences skull anatomy keeps coming up partly because it's difficult to test the various hypotheses if you only focus on primates," said Chris Kirk, anthropologist at The University of Texas at Austin.
"However, when you look at the full range of diversity across mammals, the evidence is compelling that bipedalism and a forward-shifted foramen magnum go hand-in-hand," Kirk added.
For the study, the team compared the position and orientation of the foramen magnum in 77 mammal species, including marsupials, rodents and primates.
Their findings indicate that bipedal mammals such as humans, kangaroos, springhares and jerboas have a more forward-positioned foramen magnum than their quadrupedal close relatives.
"We've now shown that the foramen magnum is forward-shifted across multiple bipedal mammalian clades using multiple metrics from the skull," added Gabrielle Russo, Assistant Professor at Stony Brook University.
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