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The Slight Difference

There are only some 3,000 differences between the human and Neanderthal genome that are predicted to affect gene expression, writes Virginia Hughes at her Only Human blog.

"But if our DNA is so similar to Neanderthals, why were they so … different?" she asks. "They were brawnier than our ancestors, with short but muscular limbs, and big noses and eyebrows. They didn't carry certain genetic variants that put modern humans at risk of autoimmune disease and celiac disease."

Epigenetics and how the genome is regulated, she says, could be at the root of those differences. For instance, Hughes notes that researchers have found that the Neanderthal HOXD9 and HOXD10 genes, which are involved in limb differentiation, were heavily methylated while the human versions of those genes are not. Further, she adds that genes that are differentially methylated in Neanderthals and humans are twice likely to be involved in disease.

Hughes notes, though, that "[s]cientists still don't really know how to interpret epigenetic changes in living people (whose diet, exposures and medical history can be tracked, however crudely). What epigenetic differences say about ancient species is even more mysterious."