The BRICS TimesSubtle Gene Shifts Transformed Ancestors’ Hips, Paving the Way for Bipedalism
Two minor genetic alterations redesigned the human pelvis. These shifts started our early ancestors toward walking upright, scientists explained.
How Two Genes Sparked Bipedalism
One genetic change rotated the ilium bone by 90 degrees. This is the bone where your hands rest on your hips. The rotation moved the muscles attached to the pelvis. It changed a system for climbing and running on all fours. It became a new system for standing and walking on two legs. The second change slowed the hardening of the ilium. It goes from soft cartilage into bone more slowly. Evolutionary biologist Gayani Senevirathne and colleagues reported this in the September 25th Nature. The outcome is a distinct bowl-shaped pelvis. This shape provides vital support for an upright body.
A New Perspective on Primate Movement
Nonhuman primates can walk upright somewhat. However, they usually move using all four limbs. The newly found changes in human pelvic growth were crucial. They created and shifted muscles, says coauthor Terence Capellini. These muscles were typically at the back, pushing the animal forward. Now they moved to the sides. This helps us maintain an upright posture while we walk.
The Science Behind the Change
Researchers studied tiny slices of developing pelvic tissue. They used samples from humans, chimpanzees, and mice under a microscope. They also used CT imaging for comparison. The human ilium cartilage grows sideways, not vertically, the team noted. Furthermore, the cartilage hardens into bone more slowly. This applies compared to nonhuman primates and other human body parts. These combined changes allow the pelvis to widen. It also keeps its broad, bowl-like shape as it develops.
Gene Rewiring: The Evolutionary Leap
Genetic analysis connected these changes to biological on-off switches. These switches manage gene activity. In humans, cartilage-forming genes became active in specific regions of the growing ilium. This prompted the bone to grow horizontally. Bone-forming genes activated later and in different areas. This delayed the hardening process. It allowed the cartilage to expand sideways. This extended growth time shapes the short, wide pelvis. It provides stability for two-legged walking.
Since developmental genes are similar across primates, the team made an inference. They suggest this gene rewiring occurred early in the hominid line. It happened after humans separated from chimpanzees. The findings support a key idea in evolutionary developmental biology. Significant anatomical changes often result from minor shifts. These shifts are in the timing and location of gene activity. They do not come from entirely new genes.
“What Terry’s work shows is it’s a different way of growing,” said anthropologist Carol Ward. “It’s not just a rotation.” She added that one significant point is how critical it was. It established the ability to stand on one foot at a time. This allows us to walk on two feet.
From Biomedical Research to an Evolution Story
The team’s research didn’t start as an evolution investigation. The National Institutes of Health funded the study. Scientists were examining how the pelvis and knees form. Their goal was to better understand hip disorders. “It was geared towards biomedical research,” Capellini stated. The aim was “understanding how you build a pelvis and why it’s different… and more importantly, why it leads to disease.”
An Unexpected Trade-Off
Ironically, the changes enabling walking may have a downside. They could make our hips more susceptible to osteoarthritis. This condition is much more common in humans than other primates.
Capellini also speculates about another potential impact. Wider hips might have led to a roomier birth canal. This could have facilitated the later evolution of larger-brained babies. “It’s an interesting kind of theoretical question,” he concluded. “But it could actually have been a practical facilitator of future brain evolution.”
