Brett Smith for redOrbit.com – Your Universe Online
With Neanderthals and modern humans sharing more than 99.8 percent of their genetic material, the differences in DNA between the two species are fairly minimal and a new study has found that the differences seen in phenotypes are mostly caused by certain genes being “switched on” or “switched off.”
According to the study published in the journal Science, genetic switches that affect the size and shape of limbs, as well as those that affect the development of the brain, are the most pronounced differences.
The study brings up the importance of researching the epigenome, or the genetic aspects that are responsible for switching on or off certain genes. Recent research has revealed how the epigenome can affect everything from cancer risk to the subtle differences between identical twins, each of whom have a copy of the same genetic material. The switching off of genes is typically achieved through a process called methylation – in which a methyl group, comprised of a carbon atom and three hydrogen atoms, is attached to a gene.
To uncover the epigenomic differences between Neanderthals and moderns humans, scientists took genetic material from limb bones of a living person, a Neanderthal and a Denisovan – an extinct Stone Age human that lived in Eurasia.
The study team was able to find approximately 2,200 regions that were triggered in today’s humans, but switched off in either or both extinct species, or the other way around. One of the main differences identified by the team was a group of five genes called HOXD, which impacts the appearance and size of limbs. It was mainly silenced in both ancient species, the scientists said. The HOXD differences could explain Neanderthals’ characteristic shorter limbs, bowleggedness and oversized hands and fingers.
Chris Stringer of the Natural History Museum in London, who was not directly involved in the study, told Reuters that the HOXD gene finding “may help to explain how these ancient humans were able to build stronger bodies, better adapted to the physical rigors of Stone Age life.”
The study team noted that the epigenome can be affected by lifestyle and environmental factors. This means that the differences observed could be unique to the individual sampled – rather than being representative on an entire species.
The researchers also found major epigenomic differences with respect to genes known to be related to neurological and psychiatric disorders such as autism and Alzheimer’s disease. These genes were silenced in the Neanderthal samples.