The question of why humans develop osteoarthritis and joint disease as they age, while our closest relatives, chimpanzees and gorillas, almost never do, has puzzled researchers. For example, 60-year-old chimpanzees are almost as agile as younger ones when climbing trees.
A stiff back and sore knees are therefore something characteristic of humans. Now researchers from Japan and Israel have published a study in Nature with the theory that this is an evolutionary price for other human characteristics.
The researchers have mapped genes that control skeletal development and have found, among other things, that the production of glycosaminoglycans (GAGs) is significantly lower in humans than in our closest relatives. These sugar molecules are found in cartilage and without them, the cartilage becomes thinner and less shock-absorbing. The bones begin to rub against each other, paving the way for osteoarthritis.
But they are also found in the brain, where lower levels make the brain more malleable over time. This may have contributed to humans being able to learn increasingly complex skills.
Lower levels of GAGs may also have benefited human survival, as they are believed to have led to a lighter skeleton that is efficient for running long distances to, for example, find food and hunt.
