People who suffer from lower back problems are more likely to have a spine similar to that of the chimpanzee, our closest ape ancestor, researchers say.
Back pain can result from a lesion known as a Schmorl's node, a small hernia which can grow in the discs between the spinal vertebrae.
Those discs would be subject to the changing shape of those bones as humans evolved from using four legs to two legs, they explain.
The researchers examined the vertebrae of chimpanzees, orangutans and ancient human skeletons to investigate the relationship between the shapes of the bones of the spine and upright movement.
Since humans are more prone to lower back pain than other primates, scientists have long wondered about a possible link between the evolution of upright walking and back 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," says biological anthropologist Kimberly Plomp of Simon Fraser University in British Columbia, Canada.
"However, evolution is not perfect and some vertebral characteristics, such as the ones we 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," she explains.
Humans and chimpanzees diverged from a common ancestor about 8 million to 9 million years ago, after which the human lineage evolved to be bipedal, walking on two rear legs, while the chimpanzees evolved to be "knuckle-walkers," she says.
Plomp has spent years studying ancient bones for evidence of disease and injury that provide insights into our ancient ancestors' health and lifestyles.
She has recently investigated the relationship between vertebrae shape, upright two-legged locomotion and human spinal health.
Schmorl's nodes - and resulting back problems - tend to show up in people whose vertebrae are more similar to those seen in chimps, she says. The nodes are believed linked to stress and strain on the lower back.
"The humans that have Schmorl's nodes tend to have vertebral elements with a shape that is statistically indistinguishable from chimpanzee vertebrae," she says.
Plomp says that what she calls an "ancestral shape hypothesis" might also be a factor in other spinal diseases such as osteoarthritis.
The researchers' study has appeared in the journal BMC Evolutionary Biology.
Photo: William Warby | Flickr
