Comparative Intrinsic Foot Muscle Size in Humans and Other Apes

open_access
Open Access
Author:
Miller, Paige
Area of Honors:
Anthropology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
Nicholas Holowka, Thesis Supervisor
Laurel Nichole Pearson, Thesis Honors Advisor
Keywords:
Intrinsic foot muscles
Human evolution
human foot evolution
evolution
Anthropology
Anthropological Science
Bipedalism
Abstract:
Humans have a very distinct foot compared to non-human apes, which allows us to walk bipedally with ease. I hypothesize that there will be differences in the musculature of human feet compared to non-human apes. Specifically, those muscles that move apes’ opposable thumb like adductor hallucis. I also hypothesize that muscles that support humans’ longitudinal arch will be larger, especially quadratus plantae and abductor hallucis. This study looked at ten human subjects, one chimpanzee, one gorilla, on bonobo, and four orangutans. Previously published data lacked normalizations by body mass, which does not allow for interspecies comparisons. Using MRI imaging I was able to segment my human subjects’ foot muscles and calculate their mass, which allowed me to compare the values to pre-published non-human ape data. I found that the biggest difference between humans and apes was a consistent appearance of quadratus plantae in humans. Even when normalized for body mass, humans had smaller muscles overall which could indicate benefit of a smaller foot for bipedal walking. I also found that humans have a larger adductor hallucis oblique head compared to all the non-human apes except for the orangutans. This has implications for two evolutionary uses of the muscle.