Monday April 27 2015
Chimpanzees are our closest living non-human relative
"People with lower back problems are more likely to have a spine similar in shape to the chimpanzee," BBC News reports. Research suggests that humans with similar shaped vertebrae to chimps are more vulnerable to developing a slipped disc.
Back pain is a common problem that affects most people at some point in their life and is one of the leading causes of what is known as a slipped disc – when one of the discs that sit between the bones of the spine (the vertebrae) is damaged and presses on the nerves.
But our knuckle-walking ape cousins don’t suffer nearly as much. One explanation is that our back problems are due to the extra stress placed on our backs from standing upright.
Scientists studying the vertebrae of chimpanzees, medieval humans and orangutans found humans with disc-related back problems had spines more similar in shape to chimpanzees.
Back problems in this study were defined as the presence of a lesion called a Schmorl's node; they are most often seen in people who have a slipped disc and can be a general sign of degeneration in the spine, though their significance is not completely understood. The participants, however, were long dead, so we don’t actually know if they had back pain.
The researchers think this knowledge could be used to identify people who are more likely to have back problems, based on the shape of their spines. This is plausible, but not yet a reality.
Where did the story come from?
The study was carried out by researchers from Universities in Canada, Scotland, Germany and Iceland. It was funded by the Social Sciences and Humanities Research Council, Canada Research Chairs Program, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, MITACS, and Simon Fraser University.
The study was published in the peer-reviewed science journal BMC Evolutionary Biology. This is an open-access journal, so the study is free to read online.
Generally, the UK media reported the story accurately, avoiding the common pitfall of saying, or implying, that humans have evolved from chimps. This is not the case. We both have a common ancestor, so are cousins, albeit cousins who shared a grandparent 5-10 million years ago.
Many articles suggested that the finding may help identify people at a higher risk of back pain, such as athletes. However, any implications from this study are not completely clear, and we don’t yet know how useful this knowledge would be in practice.
What kind of research was this?
This was an evolutionary study looking at the spines of human and non-human primates to see how differences might relate to back problems.
Back pain is a common problem that affects most people at some point in their life. However, our ape cousins don’t suffer nearly as much. One explanation is that our back problems are due to the extra stress placed on our backs from standing upright. Non-human apes don’t walk upright nearly as much as humans.
Our ape ancestors' vertebral shape would not have been adapted for walking upright. Because of this, the research team predicted that people whose vertebrae were at the more ancestral end of the range of shape variation can be expected to suffer disproportionately more from load-related spinal disease.
What did the research involve?
The last thoracic (upper back) and first lumbar (lower back) vertebrae from 71 humans, 36 chimpanzees and 15 orangutans were scanned using computers and compared in detail for subtle differences in their shape and position of bony landmarks.
The human vertebrae were from skeletons dug up from the medieval and post-medieval period, while chimpanzee and orangutan vertebrae were a mix of wild and zoo animals from US Natural History museums.
Of the human vertebrae, about half had Schmorl’s nodes, and half did not. The spine is made up of stacks of bone (vertebrae) and discs (cartilage), making the spine both strong and moveable. The nodes are small bulges of the cartilage disc into the adjacent bony vertebrae.
They are most often seen in people who have a slipped disc and may be a general sign of degeneration and inflammation in the spine.
However, the nodes' significance in slipped discs and back pain is not completely understood. For example, some people who have them have pain, while others do not. For the purposes of this research, vertebrae with the Schmorl’s nodes were referred to as “diseased” and those without referred to as “healthy”. None of the non-human ape vertebra were classed as diseased.
They fed all the information into a statistical model to predict spine health for human and non-human apes.
What were the basic results?
The predictive model was able to show there were differences in the vertebrae in healthy humans, chimpanzees and orangutans. Crucially, it found no difference between diseased human vertebrae and chimpanzees.
This suggested that humans with Schmorl’s nodes are closer in shape to chimpanzee vertebrae than healthy human vertebrae.
How did the researchers interpret the results?
The research team concluded: "The results support the hypothesis that intervertebral disc herniation [a "slipped disc"] preferentially affects individuals with vertebrae that are towards the ancestral end of the range of shape variation within H. sapiens [modern humans] and therefore are less well adapted for bipedalism [walking upright on two legs]. This finding not only has clinical implications, but also illustrates the benefits of bringing the tools of evolutionary biology to bear on problems in medicine and public health."
This evolutionary research used a small sample of vertebrae from humans, chimpanzees and orangutans to show that people with a disc bulge had spines more similar in shape to chimpanzees than healthy humans. The research team took this as a sign that people with vertebrae shape more similar to chimpanzees may be more likely to have disc-related back problems because they are less well adapted, evolutionary speaking, to walking upright.
The main limitation of the study is the use of Schmorl’s nodes to label spines as "diseased" vs. "healthy", and to assume the presence of the nodes was a sign of back pain. Obviously, the skeletons could not be asked whether they experienced back pain. The significance of Schmorl’s nodes is still not completely understood. Not everyone with them has back pain, so the results are less widely applicable than they may appear.
The study also used a relatively small number of vertebrae to reach its conclusions. The reliability of the findings would be improved if they were replicated using more vertebrae.
The implications of the study were summed up by lead scientist Dr Kimberly Plomp, in The Daily Telegraph, who said: "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."
This may be possible, but at this stage in the research, we can’t draw any firm conclusions.
The study isn’t applicable to all back pain, only those related to specific disc bulges. The findings are not relevant to the large number of people with general mechanical back pain, without specific cause, or to people with other disease or injury causes of back pain.
For advice on how to prevent and treat back pain, visit the NHS Choices Back Pain Guide.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.