Updated: Mar 7, 2021
Several theories postulate how humans evolved to stand upright on their two feet while their closest cousins, chimpanzees, remained quadrupedal.
Human bipedalism was deemed a product of Darwinism's natural selection theory that represented it as a favorable trait among early hominins.
The question is, how did it all begin and why?
Well, the origin of bipedalism was not particular to one event. In fact, there were many possibilities to its beginning that constituted an evolutionary timeline of hominin species.
The first of these speculations was the savanna-based theory.
As human ancestors began exploring vast areas of terrain, researchers argued they no longer needed to hang from trees but rather had to adapt to the openness around them. To do so, they remained erect on their two feet to gain a clear view of the land and make themselves more intimidating to predators. However, early fossil records indicated that early bipedalism was present in hominins that were accustomed to tree-climbing as well, which meant that this concept likely began in the trees.
Thus, the postural feeding hypotheses were developed.
Cultivated by Kevin Hunt at the University of Indiana, this speculation correlated bipedalism with favorable habits that were involved in the obtainment of food. Hunt noted that chimps appeared only bipedal when they ate. To reach high-up fruits, they stood on their two legs to gain balance and easier access to upper branches. This quality was also evident in Australopithecus Afarensis who had shoulders built for hanging in trees and legs meant for standing. Therefore, Hunt argued that bipedalism began as a feeding stance that allowed early hominins to gain easier access to their meals.
Yet, ancient ancestors of both chimps and humans exhibited ambiguous qualities that were both quadrupedal and bipedal. As years of evolution took place, scientists believed that the chimp and human species branched off separately from these ancestors and developed further into either the quadrupedal or bipedal trait.
Among all great apes, however, humans were the only ones to remain fully bipedal.
So, why was this the case? What exactly did bipedalism do for our species throughout history?
Several models can help further explain the theories to answer these questions.
The threat model is closely related to the Savannah-based theory as it established bipedalism as a form of intimidation that largened the stance of early hominins. Being out in the open with carnivores all around, standing upright on two feet created an exaggerated image that could scare off any potential predators.
Another model called the thermoregulatory model suggested that bipedalism allowed ancient hominins to dissipate heat easily. Being upright would allow these individuals to reach higher elevations and cooler winds that would make them ultimately more comfortable.
Yet, there are many disadvantages to bipedalism that counter the proposed benefits. Researchers know that bipedal organisms are far less quick compared to quadrupeds. If early hominins needed to avoid predators, then their bipedal legs were sure to be outrun. Additionally, the concept of dissipating heat in organisms is present in several animal species that are not bipedal. Examples including, frogs, snakes, and owls.
So, why? Why were humans the only ones to fully adopt bipedalism?
Researchers believe that the full mobility of early hominins' legs freed their hands for other uses unrelated to movements, such as toolmaking and weaponry. As humans branched from chimps and used their hands more, they were able to defend themselves and create tools that helped them survive. Such an advantage overshadowed their lessened speed and enabled them to flourish. Thus, they passed on the trait of bipedalism down through generations because of how beneficial it was.
Despite these many findings, however, more research is required. Studies have shown that the evolution of human bipedalism began with the postural feeding hypotheses and further developed from there.
There seemed to be a combination of factors that played a role in our modern structure, but for now, we have made some stark discoveries.
Our ability to stand proudly and reach the top cupboards in the kitchen can all be dated back to our ancestors trying to reach fruits in the trees.
So, theoretically speaking, we can all thank them for being hungry and doing something about it.