"The variant that decreases height is lowering the activity of GDF5 in the growth plates of the bone." said Terence Capellini, Associate Professor at the Harvard University.
According to a new study, the same gene mutation that helped our human ancestors survive frostbite might have also led to the development of arthritis.
According to researchers at Stanford and Harvard universities, a variant of the GDF5 gene - which is associated with bone growth and joint formation - has two effects on those that carry mutations of the gene: it reduces bone length (and, subsequently, height), and it can nearly double the chance of osteoarthritis. It's thought that at least half of Europeans and Asians have the gene variant, yet it remains relatively rare in African populations.
"Interestingly, having the short height variant in this region is thus linked to having an increased risk of knee and hip osteoarthritis, because of separate mutations".
For the study, published in the journal Nature, the team examined gene GDF5, first linked to skeletal growth in the early 1990s, to learn more about how the DNA sequences surrounding GDF5 might affect the gene's expression.
"So even though it only increases each person's risk by less than twofold, it's likely responsible for millions of cases of arthritis around the globe".
Further research showed that this nucleotide change has been repeatedly favoured during human evolution.
The hypothesis is that a more compact body structure with shorter bones may have helped curb the risk of breaking bones and incurring serious injury - and that the benefits conferred from this stoutness outweighed the pain and inconvenience of sore joints. The gene in question, known as GDF5, which is involved in bone growth and joint formation, also increases one's risk of osteoarthritis - a condition that causes joints to become painful and stiff.
Researchers found that the same GROW1 variant was found in the DNA of both ancient and modern humans in Europe and Asia.
In addition to lowering the risk of broken limbs, it's also possible the reduced growth made it easier to withstand other dangers that come with colder weather, thanks to less exposed skin and extremities. "When you look at animals that reside in the arctic, they tend to have shorter appendages to reduce the risk of frostbite and to maintain body heat".
While the authors acknowledge that their hypothesis about why our ancestors favoured the GDF5 variant is speculative, there's clearly something going on here, because this genetic adaption didn't only happen once.
Modern humans migrated from Africa between 50,000 and 100,000 years ago.