Scientists find the genetic clues that let humans walk on two legs

Two small changes in human DNA may have played a big role in helping our ancestors walk upright, researchers say.

The study, recently published in the journal Nature, found that these tweaks changed how a key hip bone developed.

This allowed early humans to stand, balance and walk on two legs instead of moving on all fours like other primates.

One change caused the ilium—the curved bone you feel when you put your hands on your hips—to rotate 90 degrees. This shifted how muscles attached to the pelvis, transforming a structure once used for climbing into one built for upright walking.

The other genetic change slowed down how the ilium hardened into bone, giving it more time to expand sideways and form a short, bowl-shaped pelvis.

These changes were “essential for creating and shifting muscles that are usually on the back of the animal, pushing the animal forward, to now being on the sides, helping us stay upright as we walk,” study co-author Terence Capellini, an evolutionary biologist at Harvard University, said.

The researchers examined samples of developing pelvic tissue from humans, chimpanzees and mice, pairing microscopic samples with CT imaging.

They found that in humans, pelvic cartilage grows sideways rather than vertically as it does in other primates, and that it hardens later, allowing the structure to widen as it forms.

Further analysis revealed that the difference came from subtle changes in gene regulation—the “on-off switches” that control how and when certain genes are active.

In humans, cartilage-forming genes switched on in new regions, prompting horizontal growth, while bone-forming genes activated later, slowing the hardening process.

Because primates share most of the same developmental genes, researchers believe these changes appeared early in human evolution, after our lineage split from chimpanzees.

“What Terry and his lab’s work has shown is that it’s not just a rotation, it’s a different way of growing,” University of Missouri anthropologist Carol Ward, who was not involved in the study, told Science News. “One of the most significant things about this change is it shows how critical it was to establish the ability to stand on one foot at a time, which lets us walk on two feet.”

Interestingly, this research didn’t start as an evolutionary study. Funded by the National Institutes of Health, researchers originally set out to understand how the pelvis forms to improve treatments for hip disorders.

“It was geared towards biomedical research,” Capellini told Science News, “understanding how you build a pelvis and why it’s different [from other primates and mice], and more importantly, why it leads to disease.”

What’s more, the same evolutionary adaptations that enabled walking may also have made the human hip more prone to osteoarthritis, the researchers noted.

And, Capellini added, those wider hips may have also created a roomier birth canal, making it easier for humans to give birth to larger-brained babies as evolution progressed.

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