Last month the University of Texas at Austin published results of a study linking evolution of the human skull to bipedalism which has been a point of debate in the past. According to that study the evolution of bipedalism can can be detected in fossil human remains using a key feature of the skull.
At the base of the skull is a large hole where the spinal cord connects to the brain known as the “foramen magnum.” When we compare that hole with other primates we find that in humans it is positioned forward toward the center of the base of the skull whereas in other non-bipedal mammals it tends to be more at the rear of the skull.
Scientists have theorized that the reason for this difference in humans is connected with bipedalism and the need for balancing the head directly atop the spine which is necessary for walking on two legs. Although most researchers believe this is the case some have not. The controversy has gone on since 1925!
In that year Raymond Dart made references to Taung Child, a young Australopithecus africanus specimen, which is dated at 2.8 mya. Dart discussed the position of the formen magnum in this species believing its center position enabled humans to be bipedal. Then last year Aidan Ruth and colleagues stirred the mess up again by publishing added criticisms of the notion! I guess some people have never heard of letting a sleeping dog lie 🙂
Now just last month Gabrielle Russo of Stony Brook Unersity and colleagues at UT Austin published results of the newest study adding to the debate even further! This study added on previous research done by this same team showing that the foramen magnum and the forward positioning of it is found not only in bipedal ancient human ancestors but that it is ALSO FOUND IN OTHER BIPEDAL MAMMALS generally!! Wow talk about stirring the pot!!
The reason for the debate is it’s problematic to test the prevailing hypotheses regarding the position of the foramen magnum IF you ONLY focus on PRIMATES. When you look at other bipedal mammals it appears that bipedalism and position of the foramen magnum seem to go hand in hand!!
In this current study building on their previous work Russo and Chris Kirk at UT-Austin used some new methods and sampled the largest number of mammal species to date in their study. They compared the position of the foramen magnum in 77 mammal species which included not only other primates but also marsupials and rodents. What they found was that bipedal mammals such as humans, kangaroos, springhares, and jerboas also have a more forward positioned foramen magnum! That is, it is further forward or centered positioned that that of quadrupedal mammals.
I’m sure this will NOT settle the debate over bipedalism and the position of the foramen magnum but it does add more ammo to those who support the hypothesis that a centered position evolved to balance the head on the spinal column thus enabling bipedalism. Further, can you imagine if your foramen magnum was at the rear of your skull and how low your head would hang? It might get breaking heavy carrying such an imbalanced weight! Myself I happen to be in the same camp as Russo and Kirk, in that, I do believe as bipedalism developed in our ancient ancestors that the foramen magnum became positioned forward and centered to enable balancing our heads on our spinal columns. I’m sure the debate will continue and that’s for sure. But, then again, we who study such things LOVE to debate and even argue don’t we?