How Two Small Genetic Changes Helped Early Humans Walk Upright

Two tiny DNA tweaks, a big change in how we move

A new study published in Nature reports that two subtle changes in gene regulation altered how a key hip bone develops, enabling early humans to stand, balance and walk on two legs. Researchers say these developmental shifts remodeled the ilium - the curved hip bone you feel when you place your hands on your hips - turning a pelvis adapted for climbing into one optimized for upright bipedal locomotion.

What the researchers found

One regulatory change rotated the ilium by roughly 90 degrees, which shifted where major muscles attach to the pelvis. The second change delayed ossification, the process by which cartilage hardens into bone, giving pelvic cartilage extra time to expand laterally. Together these changes produced a shorter, bowl-shaped pelvis that helps keep the body balanced over a single supporting leg during walking.

How they reached the conclusion

The team compared developing pelvic tissues from humans, chimpanzees and mice using microscopic analysis paired with CT imaging. They observed that human pelvic cartilage grows more horizontally than it does in other primates, and that ossification occurs later in humans, allowing the pelvis to widen as it forms. Further experiments pointed to alterations in gene regulation - the biological on-off switches that determine where and when genes are active - rather than changes in the genes themselves. In humans, cartilage-promoting genes are activated in new regions while bone-promoting genes switch on later, producing the observed growth pattern.

Evolutionary and medical implications

Because primates share most developmental genes, the researchers infer these regulatory changes emerged after the human lineage split from chimpanzees and helped establish a new mode of growth, not merely a rotated bone. University of Missouri anthropologist Carol Ward, who was not involved in the study, noted that the finding represents a fundamentally different growth pattern that supports the ability to stand on one foot at a time, a key element of efficient bipedal walking.

The work began as NIH-funded biomedical research aimed at understanding pelvic development to improve treatments for hip disorders. The investigators also suggest the same evolutionary changes that enabled bipedalism may have increased human vulnerability to hip osteoarthritis. Conversely, a wider, bowl-shaped pelvis likely made the birth canal roomier, helping early humans give birth to infants with larger brains as our species evolved.

“It was geared towards biomedical research,” said study co-author Terence Capellini (Harvard University). “We wanted to understand how you build a pelvis, why it differs from other primates and mice, and why those differences can lead to disease.”

Where to read more

For broader context on human evolution, see resources such as the Smithsonian's Human Origins Program. The Nature paper provides the technical data and methods behind these findings.