People with closer links to their ape ancestors may be more prone to a common cause of back pain, a study has shown.
Evidence suggests that individuals with chimpanzee-like vertebrae are at greater risk of suffering a slipped disc.
Bad backs may partly be the result of learning to run before we could walk in evolutionary terms, scientists believe.
The rapid evolution of our ability to walk upright on two legs appears to have left some people vulnerable to back trouble.
Lead scientist Dr Kimberly Plomp, from Simon Fraser University in Canada, said: “Our study is the first to use quantitative methods to uncover why humans are so commonly afflicted with back problems compared to non-human primates.
“The findings have potential implications for clinical research as they indicate why some individuals are more prone to back problems.
“This may help in preventative care by identifying individuals, such as athletes, who may be at risk of developing the condition.”
Slipped disc, or “intervertebral disc herniation”, affects between 20% and 78% of individuals depending on the population.
It happens when cushioning pads of cartilage between vertebrae split and release a gel-like substance that puts pressure on spinal nerves.
The cause is not always clear but age is thought to be a factor, making spinal discs less flexible and more likely to rupture.
Dr Plomp’s team compared the vertebrae of 141 humans, 56 chimpanzees and 27 orangutans, each of which have a different mode of locomotion.
While humans habitually amble on two feet, chimps mostly walk on their knuckles while orangutans use all four limbs to climb trees. All have significantly different shaped vertebrae.
The study found that human vertebrae with a common hallmark of “vertical” slipped disc known as “Schmorl’s nodes” looked more like those of chimpanzees than healthy vertebrae.
Slipped discs producing the symptom – protrusions of cartilage – were more likely to affect people “towards the ancestral end of the range of human shape variation”, said the researchers.
Such individuals may be less well adapted for bipedalism, they claimed.
The findings are published online in the journal BMC Evolutionary Biology.
Future research will include larger sample sizes and multiple human populations from different ancestral backgrounds, as well as the results of CT scans of living people.