How Tiny DNA Tweaks Changed How We Walk

Humans stand out among primates because they walk on two legs. This ability didn't just happen by chance. It turns out, two small changes in our DNA played a big role in this unique trait. Researchers recently made an exciting discovery. They found that these genetic tweaks altered how a key hip bone, called the ilium, developed. This change allowed early humans to stand, balance, and walk upright instead of moving on all fours like other primates. One of these changes caused the ilium to rotate 90 degrees. This rotation shifted how muscles attached to the pelvis. It transformed a structure once used for climbing into one built for upright walking. The other change slowed down how the ilium hardened into bone. This gave it more time to expand sideways and form a short, bowl-shaped pelvis. These changes were crucial. They helped create and shift muscles that are usually on the back of animals to the sides. This shift helps us stay upright as we walk. Researchers examined samples of developing pelvic tissue from humans, chimpanzees, and mice. They paired microscopic samples with CT imaging to make this discovery. They found that in humans, pelvic cartilage grows sideways rather than vertically as it does in other primates. It also hardens later, allowing the structure to widen as it forms. Further analysis revealed that the difference came from subtle changes in gene regulation. These are the “on-off switches” that control how and when certain genes are active. In humans, cartilage-forming genes switched on in new regions. This prompted horizontal growth, while bone-forming genes activated later. This slowed the hardening process. Because primates share most of the same developmental genes, researchers believe these changes appeared early in human evolution. They likely occurred after our lineage split from chimpanzees. This research didn't start as an evolutionary study. It was originally funded to understand how the pelvis forms to improve treatments for hip disorders. Interestingly, the same evolutionary adaptations that enabled walking may have also made the human hip more prone to osteoarthritis. Those wider hips may have also created a roomier birth canal. This could have made it easier for humans to give birth to larger-brained babies as evolution progressed.