While purebreds of animals may have expressed consistency of traits and favored by some, genetic diversity due to interbreeding has been critical to our survival. A recent study indicates that our ancestors have mated with their evolutionary cousins, leading to the formation of our modern immune systems. How has this affected us today?
Apparently genes from Neanderthals contributed some 4% of modern Eurasian genomes while Denisovans contributed 4-6% of modern Melanesian genomes that help us cope with viruses to this day.
Hundreds of thousands of years ago, ancient humans from Africa split into several groups, among them Homo Sapiens (modern humans), Neanderthals and Denisovans. While the Neanderthals moved into West Asia and Europe, the Denisovans moved further into East Asia. However the ancestors of modern humans left Africa much later, beginning some 65,000 years ago, and started living together with the Neanderthals and Denisovans.
In a recently published study, an international team of researchers lead by Stanford University scoured the Neanderthal and Denisovan genomes for genetic variants central to our immune system. These genes known as the HLA Class I genes govern the body’s immune system in identifying and destroying foreign bodies.
"The HLA genes that the Neanderthals and Denisovans had, had been adapted to life in Europe and Asia for several hundred thousand years, whereas the recent migrants from Africa wouldn't have had these genes," said study leader Peter Parham from Stanford University School of Medicine in California.
"So getting these genes by mating would have given an advantage to populations that acquired them."
Due to the interbreeding and further migration, one particular combination of the Denisovan gene is present at frequencies of over 50% in China and Papua New Guinea but totally absent in Africa. On the other hand, Neanderthals which mated much earlier with modern humans had their genes brought into Europe and Asia.
As of now, this is the first published case of strong evidence that modern humans have retained DNA sequences from archaic humans due to survival. Ironically the HLA genes not only strengthened human’s immune system, it also led to our susceptibility to autoimmune diseases.
“There's enormous genetic variation in people's immune systems and that can control how different people fight different diseases. This could go some way to explaining why some people are better at fighting some infections than others, but we think it also goes some way to explaining why some people are susceptible to autoimmune diseases,” said Paul Norman, co-author of the paper.
Autoimmune diseases are illnesses that occurs when the immune system mistakenly identify our body as foreign and begins attacking it.
"The vast majority of autoimmune diseases have been shown by genome-wide association studies to be associated with particular HLA alleles and we find a couple of those in Denisovans," added Norman. "So it looks to me like modern humans have acquired these alleles, but we weren't kind of prepared for them, we hadn't grown up with them, and in some circumstances, they can start to attack us as well as the viruses and other pathogens."
So back to the question mentioned earlier, not on sleeping around, but about our modern immune systems. The HLA genes have presented an efficient and effective means of strengthening our immune systems, which is great for most people. Unfortunately, a small population of the human race has to suffer from its imperfection as well.
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