Humans share a heavy biological price for walking upright and developing large brains, according to an Israeli study.
Research led by Associate Prof. David Gokhman of the Weizmann Institute of Science in Rehovot, alongside a team from Kyoto University in Japan, reveals why human joints degenerate while chimpanzees and gorillas remain agile into old age. The findings were published in the journal “Nature” under the title “The gene-regulatory evolution of the human skeleton.”
Unlike other great apes whose joint composition has remained unchanged for millions of years, human joints underwent a dramatic evolutionary shift.
That shift made our joints less effective at absorbing shocks and exposed us to skeletal diseases – including osteoarthritis, degeneration of the spinal discs, and herniated discs – that are uncommon in other great apes, including those that reach old age.
David Gokhman, molecular geneticist
The research team, which included doctoral students Nadav Mishol from Gokhman’s lab and Yizhi Yan from Fumitaka Inoue’s lab at Kyoto University, spent five years on the study. Japanese researchers identified 15,077 regulatory elements with human-specific activity, with a few hundred involved in the GAG pathway, while the Israeli team handled the analysis.
The reduction in GAG content affects the entire body, appearing across all eight joints studied, including hips, elbows, shoulders, wrists, and fingers. According to Mishol, humans start life with much less cartilage, suggesting the trait is present at birth.
While GAGs are essential for cartilage, they are also abundant in the nervous system, where they stabilize connections between neurons. Lower GAG levels may have allowed the human brain to remain exceptionally malleable for much longer than in other great apes, giving humans more time to learn and adapt.
If there is less GAG, the brain develops more slowly over 20 years, but we pay for this in our skeletons.
David Gokhman, molecular geneticist
Because cartilage has almost no capacity to regenerate, decades of use gradually erode the limited reserve, making joint disease much more likely later in life. By contrast, chimpanzees that live into their 60s or 70s show almost no signs of skeletal disease and remain agile while climbing trees.
