Science, Tech, Math › Animals & Nature The Bipedalism Hypothesis in Human Evolution Share Flipboard Email Print Getty/Nicholas Veasey Animals & Nature Evolution Human Evolution History Of Life On Earth Natural Selection Evolution Scientists The Evidence For Evolution Resources Amphibians Birds Habitat Profiles Mammals Reptiles Insects Marine Life Forestry Dinosaurs View More By Heather Scoville Science Expert M.A., Technological Teaching and Learning, Ashford University B.A., Biochemistry and Molecular Biology, Cornell University Heather Scoville is a former medical researcher and current high school science teacher who writes science curriculum for online science courses. our editorial process Heather Scoville Updated January 02, 2018 One of the most obvious characteristics shown by humans that is not shared by many other animal species on Earth is the ability to walk on two feet instead of four feet. This trait, called bipedalism, seems to play a large role in the pathway of human evolution. It does not seem to have anything to do with being able to run faster, as many four-legged animals can run faster than even the fastest of humans. Of course, humans do not worry much about predators, so there must have been another reason bipedalism was chosen by natural selection to be the preferred adaptation. Below is a list of possible reasons humans evolved the ability to walk on two feet. 01 of 05 Carrying Objects Long Distance Getty/Kerstin Geier The most accepted of the bipedalism hypotheses is the idea that humans began walking on two feet instead of four in order to free their hands to do other tasks. Primates had already adapted the opposable thumb on their forelimbs before bipedalism happened. This allowed primates to grasp and hold smaller objects other animals were incapable of grabbing with their forelimbs. This unique ability could have led to mothers carrying infants or gathering and carrying food. Obviously, using all fours to walk and run limits this type of activity. Carrying an infant or food with the forelimbs would necessitate the forelimbs be off the ground for long periods of time. As early human ancestors migrated to new areas around the globe, they most likely walked on two feet while carrying their belongings, food, or loved ones. 02 of 05 Using Tools Getty/Lonely Planet The invention and discovery of tools may also have led to bipedalism in human ancestors. Not only had primates evolved the opposable thumb, their brains and cognitive abilities had also changed over time. Human ancestors started problem-solving in new ways and this led to the use of tools to help make tasks, such as cracking open nuts or sharpening spears for hunting, easier. Doing this sort of work with tools would require the forelimbs to be free of other jobs, including helping with walking or running. Bipedalism allowed the human ancestors to keep the forelimbs free in order to build and use the tools. They could walk and carry the tools, or even use the tools, at the same time. This was a great advantage as they migrated long distances and created new habitats in new areas. 03 of 05 Seeing Long Distances Science Picture Co/Getty Images Another hypothesis as to why humans adapted by walking on two feet instead of four is so they could see over tall grasses. Human ancestors lived in untamed grasslands where the grasses would stand several feet in height. These individuals could not see for very long distances because of the density and height of the grass. This could possibly be why bipedalism evolved. By standing and walking on only two feet instead of four, these early ancestors nearly doubled their height. The ability to see over the tall grasses as they hunted, gathered, or migrated became a very beneficial trait. Seeing what was up ahead, from a distance helped with direction and how they could find new sources of food and water. 04 of 05 Using Weapons Getty/Ian Watts Even early human ancestors were hunters that stalked prey in order to feed their families and friends. Once they figured out how to create tools, it led to the creation of weapons for hunting and defending themselves. Having their forelimbs free to carry and use the weapons at a moment's notice often meant the difference between life and death. Hunting became easier and gave the human ancestors an advantage when they used tools and weapons. By creating spears or other sharp projectiles, they were able to kill their prey from a distance instead of having to catch the usually faster animals. Bipedalism freed their arms and hands to use the weapons as needed. This new ability increased the food supply and survival. 05 of 05 Gathering From Trees By Pierre Barrère [Public domain or Public domain], via Wikimedia Commons Early human ancestors were not only hunters, but they were also gatherers. Much of what they gathered came from trees such as fruit and tree nuts. Since this food was not reachable by their mouths if they were walking on four feet, the evolution of bipedalism allowed them to now reach the food. By standing upright and stretching their arms upward, it greatly increased their height and allowed them to reach and pick low hanging tree nuts and fruit. Bipedalism also allowed them to carry more of the foods they gathered to bring back to their families or tribes. It was also possible for them to peel the fruits or crack the nuts as they were walking since their hands were free to do such tasks. This saved time and let them eat more quickly than if they had to transport it and then prepare it at a different location.