The human foot has an interesting evolutionary history. Understanding this history can be helpful in assessing foot and ankle problems because there is a theory that many humans have retained some elements of foot characteristics of our evolutionary ancestors (atavistic traits). These traits may lead to conditions such as flatfeet and bunions which alter the way that the foot absorbs force when we walk. This in turn can lead to a propensity to develop symptomatic foot conditions (ex. metatarsalgia, acquired adult flatfoot deformity, bunions, plantar fasciitis, etc). This theory seems to be initially proposed by Dudley Morton (different from the Morton who described Morton’s neuroma). Morton was an anatomist at Columbia University who wrote a book entitled The Human Foot: Its Evolutionary Development, Physiology and Functional Disorders in 1935.
Here are some ideas associated with the role of the importance the evolution of the human foot:
1. Humans are one of the “Great Apes”
Along with Chimpanzees, Pygmy Chimps (Bonobos), Gorillas, and Orangutans. From a genetic point of view humans are closely related to the other great apes sharing over over 95% of our DNA. Chimpanzees share 97.3% of their DNA with humans. From a genetic point of view it has been suggested that chimpanzees are more closely related to humans than they are to gorillas.
2. The other great apes all have opposable first rays i.e. they can grab things with their feet (Figure 1)
Figure 1: Baby Gorilla using feet to grab
3. Chimps, Gorillas, and Orangutans all have pronouced gastrocnemius equinus contractures.
When you straighten their knees their feet point down and they are unable to bring their feet up to a right angle unless they bend their knees. This occurs because the outer calf muscle (the gastrocnemius) starts above the knee and is therefore under tension when the knee is straight. This anatomical setup explains why the other great apes always walk with their knees bent.
edited October 14th, 2012