Of all the mysteries generated by human evolution, the most confounding is why upright posture is an absolute requirement for a fossil to be designated as belonging to our hominid family. This determination is made usually by assessing the relative forward position of the hole in the base of the fossil skull (foramen magnum) through which the spinal cord exits. Popular hypotheses for why early hominids stood up included the ability to look over tall savanna grass or wade through swamps. Eventually bipedalism became a more energy efficient way to run, but only after the “in between” stages of posture were decidedly less efficient than the “knuckle walking” of apes.
Every orthopedic surgeon knows one fact about bipedalism that must be considered in constructing a hypothesis about why hominids stood up: upright posture makes the lower back extremely vulnerable to injury as well as leg and foot joints. Modern humans, after six million years of adaptation to bipedalism continue to pay a heavy price for our most unusual posture. It is, therefore, simple logic that such an “expensive” adaptation must have been absolutely central to the evolutionary innovation that led to the explosive proliferation into well over a dozen hominid species – in the face of the decline of apes. Furthermore, even the early forms of partial uprightness had to be essential to the reason that hominids were so successful.
I struck on a hypothesis for the need for upright posture while considering the origins of schizophrenia which I discussed in this post. I believe that the key hominid innovation from the very beginning was a sudden wholesale shift from selection at the level of the individual to selection at the level of the group. These creatures had to stand up in order to fathom their groups evolved intentions for them to collectively survive. They had to maintain constant visual contact with each other’s facial and upper body gestural expressions in order to stay on the “same page” like a musical band making small adjustments to stay in sync. So, standing up initiated our unique hominid language the hallmark of which continues to be the sharing of group intentions.