The anatomy of the modern human feet enables us to walk upright on two feet, also known as bipedal gait. The evolution of a permanent transverse and pedal arch are adaptations that help us to walk on land with two feet. Humans have dorsiflection of the metatarsal joints in the foot to help with the push-off phase and the ending stride of the bipedal gait. The transverse arches of our feet contribute to this dorsiflection of the metatarsals. We also have a stiff midfoot which allows the mid-foot and the hind-foot to lift off the group at the same time. Foot arches are a key factor in our day to day locomotion because of the mechanical advantage it gives us to propel off a surface. Apes on the other hand do not have arches in their feet because they use arboreal locomotion, meaning they spend most of their time on the trees.
Although it was known that a Hominin, Australopithecus afarensis was bipedal, it was not known if this species had a permanent transverse and longitudinal foot arch because an essential bone of the midfoot had not been found (a complete fourth metatarsal).
Ward and his collegues were able to obtain and analyze the fossil including the fourth metatarsal of A. afarensis foot and discovered that A. afarensis indeed had a permanent transverse and longitudinal pedal arch. Their paper supports that A. afarensis resembled modern day Homo Sapiens bipedal anatomy rather than ape anatomy. They measured torsion of the fourth metatarsal and data suggest that because of the increased torsion of the MT4, they can infer the presence of a transverse arch. This research shows that bipedality occured in early hominins and human foot anatomy as well as human pedal physiology occurred in early hominins. Evolution selection for terrestrial bipedality suggests that arboreal locomotion, as seen in apes and chimpanzees, were considered unfavorable.
When I read your post, I started thinking about what the repercussions of flat feet are. One of the biggest concerns for people with flat feet is knee pain. According to Gross et al. (2011), approximately one out of four men and women older than 55 years of age report knee pain on most days. Hence, this is an important issue to consider, especially if knee pain hinders people from partaking in exercise and other daily activities.
ReplyDeleteThe role of planus foot morphology (a.k.a. flat-footedness) in knee pain is discussed by Gross et al. (2011). They state that this potentially gives rise to excessive internal rotation of the lower half of the leg. When the knee experiences this unnatural mechanical twisting, there is a moderately increased prevalence of frequent knee pain and medial tibiofemoral (TF) cartilage damage. Because such a large chunk of the older adult population experiences knee pain, the authors of this study suggest that more research is needed on the precise mechanism behind planus foot morphology and knee pain. They also state there should be more focus on the role of foot orthoses (or shoe inserts) as a preventative measure.
Gross, K.D., Felson, D.T., Niu, J. et al. (2011). Association of flat feet with knee pain and cartilage damage in older adults. Arthritis Care and Research, 63(7), 937-944.
I read your blog post and was quite excited as I was a physical anthropology major in college and I was excited to get to use my background again. While it is true that the pedal arch is important to bipedal locomotion, it is important to realize that adaptations to the knee and hip are more indicative of proper bipedal motion. Australopithecus afarensis had a knee and hip that were adapted to bipedal walking however not very efficiently (Grabowski). Therefore it would have taken the early hominids a lot of energy to walk around and while they likely did they probably did not run fast merely because the were limited by the inefficiency of there knee and hip. Running long distance was probably not possible until species like Homo ergaster who had much longer long bones and a knee and hip angle that were efficient in generating the correct power for running.
ReplyDeleteGrabowski, M. W., Polk, J. D., & Roseman, C. C. (2011). DIVERGENT PATTERNS OF INTEGRATION AND REDUCED CONSTRAINT IN THE HUMAN HIP AND THE ORIGINS OF BIPEDALISM. Evolution, 65(5), 1336-1356. doi:10.1111/j.1558-5646.2011.01226.x