Evolution of the Human Foot

From the beginning of my decision to write about feet, I knew that I wanted to write about the evolution of the human foot. I think it’s important to have a basic understanding of human anatomical historical development and to acknowledge that our feet have not always looked and functioned in the way we have come to take for granted. Describing in detail the evolution of the structural changes in our feet over thousands of years would be difficult. Nonetheless, I will attempt to provide a comprehensive overview of the subject, including information that might be useful for a general understanding of foot function.

Early humans emerged between 16 and 5.3 million years ago in an era called the Miocene epoch. This period is characterized by the expansion of open vegetation systems (grasslands, deserts) and the recession of closed ones (forests). The change in the composition of temperate ecosystems resulted in the global expansion of grazing prey populations, which were previously confined to Africa.

Until recently, commonly accepted scientific theories suggested that human bipedalism arose from the loss of forested habitat and the need for our ancestors to forage and hunt in the emerging prevalent savannah. The theory also suggests that adoption of an upright posture provided humans with improved visibility over tall grass and the gave them the ability to use their hands for carrying objects.

A competing theory suggests that bipedalism evolved in the context of a forest-dwelling existence. Walking upright was useful when reaching for food in branches and avoiding predators on the ground. Early humans, according to this theory, are thought to have learned to walk in trees and retained the adaptation after they began living in and using open landscapes.

Although not fully upright yet, the human form began to adapt further to bipedalism about 5 to 7 million years ago. Fossil records show the gradual formation of a vertical passage of the central nervous system through the bottom of the skull, effectively keeping the skull on top of the spine and body. Lower limbs thickened and elongated to support hip muscles that provided support for walking. A lumbar curve was also developed to support increasingly vertical body weight distribution enabling the more efficient use of calories while searching for food. 

But it wasn’t until 2 million years ago that humans began to show signs of “Obligate Bipedalism.” This meant that running and walking became the primary forms of locomotion. In contrast, the term "Facultative Bipedalism" indicates that an animal can walk or run on two limbs, but only in exceptional circumstances. Chimpanzees can be seen exhibiting this behavior now; walking upright on two legs, but only when necessary.

Walking upright on two feet afforded several advantages. As mentioned previously, hands became free for various activities such as hunting and toolmaking. It also minimized sun exposure to the top of the head, making midday activity easier. Having eyes at an increased height from the ground made it easier to spot prey and predators. Being upright and walking or running on two feet made it less metabolically expensive to increase daily movement range. If you’ve ever done a “bear crawl” you’ll likely agree.

In terms of the foot specifically, there were adaptations to meet the requirements of walking and running long distances. The adaptations include shortened toes and an adducted (moved toward the center) opposing thumb, allowing for a longer stride. The foot also lengthened and developed a strongly padded heel for shock absorption when the heel strikes the ground, as well as an increased arch height that contributed to speed and agility.

The consequences of walking on two legs have had a broad impact on human evolution. One major benefit of having more free time due to efficient hunting and gathering was the ability to develop a larger brain, leading to enhanced cognitive abilities and the capacity to collaborate and hunt in groups.

Overall, as our ancestors transitioned from life in the trees to upright, committed bipedalism, their new anatomical arrangement supported the ability to walk and run efficiently on two feet, contributing to their survival and success.