Another day, another bit of anthropology news making waves on the internet. This one comes from a University of Manchester study presented to the British Association for the Advancement of Science Festival of Science. Bill Sellers, a primatologist spealizing in biomechanics at the said univerity, is claiming he made the discovery that humans first developed Achilles tendons more than 2 million years ago, before Homo erectus. I’ve got problems with this, and I’ll let you know why right after I get thru some basic anatomy.
The Achilles tendon is located in the lower leg, you can spot it on yourself by feeling for a dense tendonous ‘ribbon’ that extends below your calf muscle to your ankle. It functions as an attachment of the calf and soleus muscles to the calcaneus or heel bone and provides a lot of the spring and shock absorption in our gait. There’s a whole folk tale as to how this tendon got its name, which I won’t get into, because you should know about it already.
Bill Sellers is saying that he’s studied the fossil record and that what he found out is the Achilles tendon would have allowed early humans to move nearly twice as fast as before. Do you catch the mild adaptionist tone with this claim? He uses the lack of an Achilles tendon in the chimpanzees and gorillas as a reference point… or in other words, because those apes don’t have an Achilles tendon, that’s why they can’t run bipedally. That’s partly true and partly false. These apes have an Achilles tendon, but it’s very small. But, there’s a lot more to why non-human apes can’t run bipedally.
Our lineage’s ability to move around bipedally, be it running or walking, is not because of one anatomical feature over another. No one part is more significant.
I’m not doubting that the Achilles tendon isn’t important, what I’m saying is that almost the whole hominid body has an important role in allowing us and our like to walk around on two. I’ve said this before, and I don’t think people get it. From our femora to our tibiae, from our vertebrae to our pelvis, each bone and muscle involved in bipedal locomotion is unique when compared to a non-bipedal animal.
Which leads me to this image and my second point of criticism:
My second criticism is that Sellers is not the first to make the claim that the Achilles tendon is where all of ability to run comes from. So it bugs me that either he or the press is giving him all the credit for it. The first that I know of that talked about the importance of the Achilles tendon in bipedalism was my undergraduate physical anthropology professor, Adrienne Zihlman.
Others like, Dennis Bramble and Daniel Lieberman wrote to Nature in 2004, on “Endurance running and the evolution of Homo.” In their article, they outline the Achilles tendon as one of the important units in helping us be able to run. They also mention other parts of our body that help us run, like the gluteus maximus, a.k.a. our round butts, because that muscle is crucial in stabilizing the leg into the pelvis during high running speeds.
I got the above image from Bramble and Lieberman’s paper, which shows a modern human in the upper left, a Homo erectus in the upper right, a chimp in the lower left, and a australopithecine in the lower right. You can see how the muscles differ between the chimp and human, such as the larger gluteus in the humans and the presence of a larger Achilles tendon.
The point to take home, when studying human evolution, is that the entire body needs to be analyzed. Parts of our body did not evolve in a void from the others. The Achilles tendon, the long femur, the wider pelvis… all these parts and other parts are why are bipedal.
- If upright walking is so energetically favorable, why do apes still “knuckle-walk”?
- Chimpanzees Gait Energetics & The Origin of Human Bipedalism
- Study Identifies Energy Efficiency As Reason For Evolution Of Upright Walking
- Orangutans & the (possible) Origins of Human Bipedalism