Plomp says her findings show that the vertebrae of humans with disc problems are closer in shape to those of our closest ape relatives, the chimpanzee, than are the vertebrae of humans without disc problems.

"As evolution occurred our vertebrae would have changed as we evolved, from using some form of quadrupedal locomotion, using four legs, to bipedalism, using two legs," she says.

However, she adds, evolution isn't perfect and some vertebral characteristics, such as those identified as being similar to chimpanzees, may have remained within the human 'blueprint' and result in some people having vertebrae that are less able to withstand the pressures of bipedal walking.

"In short, our study suggests that the pathological vertebrae of some people may be less well adapted for walking upright," says Plomp.