Next, the team constructed a time line of when changes in some of these genes became widespread in the population, also determining whether those changes had been inherited from ancient hominins such as Neanderthals.
The researchers found that most of the changes in these genes occurred between 6,000 and 13,000 years ago, which was not surprising, given that humans transitioned from a hunter-gatherer to an agricultural lifestyle in this time period. However, three genes had seemed to change before that, right around the time that humans first encountered Neanderthals.
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These genes contained the instructions to build a family of proteins called Toll-like-receptors (TLR). These proteins - TLR 1, 6 and 10 - sit on the cell surface and bind to foreign invaders such as bacteria and fungi. This, in turn, mobilizes the rest of the immune system to fight an infection.
Separately, Kelso's team searched for the stretches of DNA that were the most similar among humans, Neanderthals and Denisovans. This hunt similarly led the team to the TLR 1,6 and 10 genes.