Human joint pain and chronic skeletal disorders may be the hidden evolutionary price we pay for the anatomical traits that define our species, according to a study published in the journal Nature.
While humans frequently suffer from debilitating conditions like osteoarthritis and spinal disc herniations, non-human great apes almost never develop them, even in advanced old age. Researchers discovered that human cartilage contains only about a third of the GAG material found in chimpanzees, gorillas, orangutans, and bonobos, leaving human joints vulnerable to everyday wear and tear.
Evolutionary Trade-Offs Behind Human Upright Posture
The evolutionary divergence made human joints less efficient at absorbing impacts.
Tomàs Marquès-Bonet, an ICREA research professor and principal investigator at the IBE (CSIC-UPF) at Pompeu Fabra University, explains that changes in the joints, combined with thin bones and long legs, likely supported the human transition to an upright posture. The team mapped these differences by creating the first comprehensive atlas of genomic regulatory characteristics distinguishing the human skeleton from our closest living relatives.
The atlas showed that human cartilage is less dense because an entire group of genes responsible for producing glycosaminoglycans (GAG) is less active than in other great apes. Without an abundance of GAG, human cartilage is thinner, less elastic, and less capable of cushioning the forces generated by everyday movement.
Cartilage Depletion and Osteoarthritis Risk
While GAG molecules themselves did not really change during human evolution, the quantity produced did. Other great apes maintain a much higher volume of GAG, which explains why they usually do not develop osteoarthritis or other joint disorders, and barely show signs of skeletal disease even when aging, unless their cartilage suffers serious damage due to trauma.
By contrast, humans are born with much less cartilage. Because cartilage almost has no capacity for regeneration, decades of use gradually erode this already limited reserve. Inoue notes that this makes joint diseases much more likely in later stages of life.
Why humans have a higher risk of osteoarthritis
Why do humans have a higher risk of osteoarthritis than chimpanzees?
Humans possess less dense articular cartilage with a lower quantity of glycosaminoglycans (GAG), which are molecules that help cushion the forces of movement.
Which specific conditions are linked to this evolutionary shift?
Researchers connect the lower quantity of GAG to a higher human predisposition to osteoarthritis, spinal disc degeneration, and herniated discs.
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