This blog will specifically be looking at the evolution of appendages and namely with case studies.
Monday, April 16, 2012
The "art" of ankles
Rolled ankle...sprained ankle...more than likely we've experienced one or the other at some point. As humans developed bipedal locomotion, we can trace the evolution of the appendages involved in such vertical movement---the ankle as one such component.
The human ankle has been compared to that of a chimp to understand the parallels and evolutionary development of this oftenly "forgotten" appendage.
One of the big differences in the ankles of both species, is that chimps exhibit much more flexion in their ankles, especially when climbing. However, humans do not have the capacity for such widespread range of motion. As for humans, our ankles aren't capable of anything like that range of movement. This flexion of chimp ankles places significant stress on the bones of that joint, which in turn affects overall bone structure.
Due to the differences in motion patterns and behavior, research has identified differences in bone makeup and patterns to best align with these differences. Ankles of present-day humans are predominately square-shape as opposed to chimpanzee elongated bones. Other differences in bone curvature and arrangement contest to the evolutionary differences in species function. These morphological features align with the chimpanzee's tree climbing activities and human walking behavior.
While all this information seems counterintuitive and in a lot of ways common sensical, I found it interesting because it made me think of the chicken or egg debate? We often think of evolutionary adaptations to occur as a result of stimuli or responses. In this case, if the ankle bones developed in response to physical tension caused by activities such as climbing, then where do we draw the line? How do we know how much was intuitive and there to begin with that allows for a chimp species to engage in climbing behaviors. At what point in our evolutionary history did we diverge? If humans evolved from ancestral chimps, what distinguished between us that enabled one to be a more climbing oriented species and one more bipedal?
Lots of questions, lots of uncertainty. Either way, it is interesting to think that every bone whether big or small or what we see as significant or not, has some purpose that we often fail to realize. We talk about injured ankles all the time, but if you were to ask someone to define what the physiological purpose of the ankle is, not many would be able to tell you. Yet again, we see that there is a special art to ankles as the bone is able to exhibit such plasticity and respond to tension placed on bones quite flexibly from sprains to evolutionary presence generation after generation.