Scientists have discovered which genes helped humans stand on two legs

Researchers from Harvard University have identified two genetic modifications that may have played a crucial role in the transition from walking on four limbs to upright posture. The results of the study are published in the journal Nature.

Both mutations affected the development of the pelvic bone - the iliac bone, the one you can feel if you put your hands on your sides. The first one changed the direction of growth of this bone, causing it to rotate about 90 degrees. As a result, the muscles became attached in a new way: from back to front and then to the sides of the pelvis, which helped stabilise the body in an upright position when walking.

The second mutation slowed the process of ossification of the iliac bone, giving it more time to grow in width. This made the pelvis more rounded and low, resembling a bowl - exactly the shape characteristic of modern humans and necessary for stability when standing upright.

"These changes were critical," explains one of the study's authors, evolutionary biologist Terrence Capellini. - They allowed the muscles to move to the side of the pelvis, providing balance when moving on two legs."

Capellini's team studied developing pelvic tissue in humans, mice and chimpanzees. By combining microscopy with CT scans, the scientists observed that in humans, pelvic cartilage tissue grows predominantly horizontally, whereas in other primates it grows vertically. They also found that in humans, the process of ossification starts later, allowing the bones to expand.

Later comparisons of gene activity showed that the reason for these differences was due to regulatory regions of DNA that switch certain genes on and off. In humans, genes responsible for cartilage formation were activated in new areas of the body, while genes responsible for bone formation were switched on later.

Since humans and primates share most of the same genes, the scientists believe that these changes occurred after the genus Homo separated from the chimpanzee lineage, that is, about 6-7 million years ago.

"It's not just a bone turn," comments anthropologist Carol Ward, who was not involved in the study. - 'It's a whole new way of growing. It shows how important the ability to stand on one leg was, because without it you can't walk steadily on two."

Interestingly, the work was not originally about evolution. The research was funded by the US National Institutes of Health to study the formation of the pelvis in order to develop new approaches to treating hip disorders.

According to Capellini, the same adaptation that gave humans a straight gait may have increased the risk of osteoarthritis - due to a wider and more unstable pelvic shape.

In addition, the widening of the pelvis, the scientists believe, may have played a role in the later emergence of a wider birth canal - which, in turn, allowed babies to be born with larger brains, pushing Homo sapiens evolution forward.