Thursday, July 26, 2012

Non-Human Genes in Our DNA

Slate has been running a series on "Blogging the Human Genome," which has been rather interesting. One in particular I wanted to share is this post entitled "Entry 9: Humans have long enjoyed nonhuman lovers—the proof is in our DNA":
Geneticists have used noncoding DNA in other types of historical analyses as well. Until the past few years, most scientists doubted that human beings had ever stooped to interbreed with Neanderthals or other archaic hominids. That view has since been routed: DNA extracted from old Neanderthal bones proves that all people of European and Asian descent have a few percent of Neanderthal DNA inside them today, equivalent to the amount they inherited from each great-great-great-grandparent.

In addition, scientists have discovered that Melanesians, the people who originally settled the islands between New Guinea and Fiji, seduced another archaic human race, the Denisovans, somewhere on the long haul from Africa to the south seas. The Melanesians still carry Denisovan DNA today. In some sense, then, neither Neanderthals nor Denisovans ever quite went extinct: Their DNA lives on in various non-African ethnic groups.

So what about ancient Africans? Did they ever have hominid paramours? Scientists had a harder time answering that question because the hot climate of Africa—unlike the cold Eurasian climate where Neanderthal and Denisovans lived—tends to destroy ancient DNA. A clever study from 2011 got around this limitation, however, and suggests that Africans did indeed indulge in inter-Homo hanky-panky.

The study’s scientists pored over the noncoding DNA of various ethnic groups in Africa, looking for funny patterns. For instance, they looked for random mutations that no other ethnic groups worldwide had. They were especially keen on finding long stretches of such funny DNA, because these stretches were probably inherited en masse from an archaic hominid. Sure enough, regions on chromosome 18, among other places, fit the bill. The study concluded that, about 35,000 years ago, some central Africans had children with an unnamed and now-extinct race of hominids. Like Europeans and Asians before them, these people couldn’t resist the temptations of nonhuman lovers.
It reminded me of this passage from the Bible: "And it came to pass, when men began to multiply on the face of the earth, and daughters were born unto them, That the sons of God saw the daughters of men that they were fair; and they took them wives of all which they chose." Genesis 6:1-2. I know that this is not what the verse is talking about, but that was the first thing to come to mind.

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