Two evolutionary changes underpinning human bipedalism have been discovered, reshaping the pelvis and enabling our species to walk upright on two legs. Researchers examined the genetic basis for bipedalism by studying stored samples of embryonic tissues from humans and various primate species, identifying a pair of genetic shifts that occurred long ago in the human evolutionary lineage.
The first innovation involved cartilage formation during embryonic pelvic development, allowing the ilium bone to morph into a short, wide, and curved shape. This adaptation helped stabilize the body for upright walking and running, while the second innovation involved a delay and rearward shift in pelvic bone formation, preserving the new advantageous shape of the ilium.
This delay allowed women to have a birth canal large enough to accommodate big-brained babies, complementing the growing brain size of our ancestors. The two genetic innovations, which occurred around 4-6 million years ago, enabled human bipedalism and freed up hands for other activities such as tool use, gathering, and carrying infants.
According to Harvard University biologist Terence Capellini, “Bipedalism is the form of locomotion that allowed our ancestors to traverse large areas and eventually the entire globe. Without these changes, human walking likely wouldn’t have been possible, and subsequent brain size increases would have been difficult to envision.”
Source: https://www.reuters.com/science/two-evolutionary-changes-underpinning-human-bipedalism-are-discovered-2025-08-27