For millennia, the hanky-panky between the ice sheets among the kissing cousins of prehistory was hush-hush.
Then Ed Green and his colleagues peeked into the gene pool and found proof that modern humans, or Cro Magnons,
get up close and personal with the Neanderthals, but that it must have happened well before they were hooking up in Ice Age Europe.
Now we know that many of us walk around with genes lightly laced — only 1 to 4 percent — with what a nonscientist might call “caveman DNA.”
Thursday night at the Linda Hall Library, Green told a full house about the Neanderthal Genome Project, which issued its first findings in two years.
Green is an assistant professor of biomolecular engineering in the Baskin School of Engineering at the University of California, Santa Cruz.
In the third in the lecture series, called “Blade and Bone: The Discovery of Human Antiquity,” he told of updated sampling that finds the DNA widely spread, from Siberian natives to Australian Aborigines to Native Americans.
But the DNA is not found in people of African descent.
This points to interbreeding in the Middle East 50,000 to 80,000 years ago, not long after the Neanderthals, followed by modern man, exited Africa.
“This population grew and expanded and colonized the world,” Green said.
Asked in an interview before the lecture if short legs or heavy brows might indicate the surfacing of a genetic “caveman” trait as some have suggested, he noted how the great majority of our genomes don’t appear to do anything, and that might be the case here.
The dispersal of the Neanderthal DNA, he said, “does appear random, even within closely related groups of people.”
Green drew a laugh from the crowd by noting that he was in a contentious field: “I was told that there are more paleoanthropologists than bones they have to look at.”
He went on to give much credit to Svante Pääbo, director of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and David Reich, a population geneticist at Harvard.
They worked with three bones, about 38,000 years old, all females, to build their first draft sequence of the Neanderthal genome.
The bones, found in a Croatian cave, were severely contaminated with bacteria and chemicals. The bones were degraded and fragmented; 96 percent of the DNA came from other organisms.
Green also went into depth about how they were able to eliminate the DNA left by people who touched the ancient bones since their discovery, tricky since we share all but one hundredth of 1 percent of the same genetic material with Neanderthals.
Enough was isolated from the ground-up bones, however, to build a 3-billion-nucleotide-long sequence with its own distinct combinations of the genetic code “letters” A, C, T and G. Since then, more DNA has come from the old bones and other finds, much improving the sequence, Green said.
This can be used for comparison with modern human and chimpanzee genomes to study cognitive development and skull structure.
Many differences have been found, from skin morphology to energy metabolism, Green said, but it’s too early to say if the gene variances mean much.
“One can do a screen very quickly to identify the genes where some change has happened, but things slow down a lot when you try to go back and figure out why the differences are there,” he said before the talk.
But, he explained, the discovery sheds light on the last 300,000 years of human change: “These are signals of evolutionary adaptations in our own genome since we split from the Neanderthals. Now we can put our finger on which of these variances came about very recently.”
Green mentioned the recent sequencing of a 30,000-year-old finger bone found in a southern Siberian cave that showed it was yet another extinct type of human, about as closely related to modern man as the Neanderthal. The bone came from about 30,000 years ago, about the time the Neanderthal line was extinguished.
Called the Denisovian, after a hermit that once lived in the cave, its DNA can be found elsewhere, but is concentrated in Papau New Guinea.
“If you have an idea how that happened, I’d love to hear it,” Green joked with his audience.
While noting that if an ape could talk, it would gush over the technology of the stone axes favored by Neanderthals, Green said, the cavemen apparently did not have what it takes — the power of abstract thought.
Asked in the interview about another recent discovery in a cave where one may have tried his hand at cave painting, Green said: “It’s just one example out of thousands of Neanderthal sites. The jury is still out.”