Why Is The Human Being Bipedal?

Why is the Human Being bipedal?

He Homo sapiens, that is, the modern human being, is one of the few species in the world that exclusively uses bipedalism to move. It is true that some close relatives, such as the orangutan, are “intermittent” bipeds, but their bone and muscle structure does not allow them to walk long distances in this way. In this sense, human bipedalism is unique among primates.

A multitude of causes have been considered to explain this extraordinary mutation among which are the disappearance of forests and the predominance of the savannah (which implied, therefore, the need to see further away), the freeing of the hands for the manufacture of tools and the energy savings of walking upright. There are supporters and detractors of all of them, and every year new discoveries emerge that shed light on the issue or, on the contrary, obscure it even more.

In today’s article we propose an approach to the possible causes of bipedalism of our species

Possible causes of human bipedalism

Next, we consider a series of possible causes that would explain why our ancestors suffered such a genetic mutation. However, before addressing the various explanations, let us sketch when and where human bipedalism appeared.

The first to walk upright?

Traditionally, experts have established the appearance of human bipedalism around 4 million years ago, based on the bone remains found. However, in light of new discoveries, our current locomotion may have appeared much earlier.

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In a study carried out in Chad and published in the journal Nature In 2022 (see bibliography) the range of years is extended to no less than 7 million. Specifically, in 2001 the remains of the Sahelanthropus tchadensis. The research team, made up of the National Center for Scientific Research (CNRS), the University of Poitiers, the University of N’Djamena and the National Development Research Center of Chad, examined 3 of the bones found, to conclude that The individual in question had the capacity for combined locomotion ; that is, he was capable of walking upright and climbing trees.

This study, among many others, establishes the possibility that our ancestors combined both locomotions for many millions of years. In reality, today’s chimpanzees are also capable of standing upright, but also of climbing to the tops of trees and moving along their branches, so we can think that the ancestors of Homo sapiens would also do it this way. In other words: in principle, bipedalism would not have been an exclusive locomotion.

In 2007, Aaron G. Filler, an expert in spinal biology, determined that the remains of Morotopithecus bishopi found in Uganda in the 1960s showed signs of having straightened the spine It was a remarkable discovery, since the Morotopithecus species dates back no less than more than 20 million years…

Filler’s research therefore opens up a question as thorny as it is interesting: were human beings and their most direct ancestors actually the first to walk upright? Or were there other earlier and directly related species that also managed to stand and walk? Furthermore, if what previously defined the human being was his bipedalism (since it differentiated him from his relatives), in view of the new results, what makes a species human…?

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Why are human beings bipedal?

These questions, like so many others, actually remain unknown. So are the reasons why these ancestors began to walk upright. We have commented that multiple explanations have been considered, which we detail below:

Emergence of the savanna

One of the traditional explanations for the appearance of bipedalism is the retreat of forests and the appearance of large areas without trees (what we call, in fact, sheet). In such a context, an animal that walks on all fours or rests on the knuckles of its hands has a lower chance of survival, since the expansion of the horizon requires a greater height to see the prey or the enemy from a greater distance.

This seems like a plausible cause, but let’s remember that recent research has confirmed that some of our ancestors already stood on trees, that is, long before the change in climate and landscape. Therefore, there are many scientists who today discard this idea.

Liberation of the hands

Another of the great explanations for human bipedalism is that, when walking upright, the front limbs are free, which allows the making of tools. Furthermore, this manufacturing of utensils stimulates the brain, which would explain not only bipedalism, but also the evolution of the human brain. However, this theory also has its detractors. In 2015, the magazine Nature published a study in which it was stated that the appearance of bipedalism and the appearance of the first stone tools were separated by no less than 3 million years, so it is difficult to see a cause-consequence.

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Energy savings

A study published in the Proceedings of the National Academy of Sciences (PNAS) and carried out by various American universities, suggests that bipedalism could have originated for obtain considerable energy savings To test it, the scientists put several humans and various chimpanzees on walking machines of the type found in gyms. It was found that humans expended only 25% of the energy that their relatives needed to perform the same exercise.

The experiment seems to prove that, indeed, bipedalism involves lower energy consumption, which millions of years ago was the difference between living or dying. In a 2007 interview for BBC World ScienceSalvador Moyá-Solá, director of the Catalan Institute of Paleontology, agreed with this hypothesis, since he considered that all adaptations that involve energy savings are linked to greater survival.

But, again, there are criticisms of this. Some scientists consider that, if bipedalism were so advantageous, there would be many other animal species that would have evolved towards it. And, although humans are not the only one (other species, especially birds, also walk on two legs) If energy saving really were the main cause of standing, there would probably be many more bipedal animals


So the issue remains somewhat obscure. Why did humans evolve to walk upright? What was the main cause? Why, if we consider that it was an adaptation to the savanna, could some ancestors who lived in trees already stand up? Was it really an energy saving? Or was it rather related to the creation of tools and, therefore, to the evolution of the brain?

The matter continues to be disputed. As new results appear and discoveries are made, these questions become clearer… or, rather, new ones appear.