SAN FRANCISCO – It’s a tale of romance from the Ice Age – and its consequences today.
Long ago, in a part of the world now known as Europe, early modern humans lived alongside the Neanderthal people – and they interbred.
A fast-growing population of humans eventually drove the Neanderthals to extinction 30,000 years ago, but the benefits of those early dalliances between the two groups live on.
The researchers, deciphering the genome of fossil Neanderthals and modern humans, report they have found in both a major group of matching immune system genes – genes the scientists say we inherited from our stocky Ice Age predecessors.
The same scientists also studied the genes of a different ancient people, the Denisovans, who were contemporary with the Neanderthals and whose meager fossils were found in a Siberian cave called Denisova. The Denisovans, the Stanford scientists said, were likely a “sister group to the Neanderthals” who apparently bequeathed genes of their immune systems to modern Melanesians – the people of New Guinea, Fiji and scores of other islands in the western South Pacific.
In a report published in the journal ScienceExpress on Thursday, Peter Parham, a Stanford microbiologist and immunologist, describes how he and 22 colleagues from five nations traced the genetic history of the varied people who originated in Africa and later moved into Europe and the Middle East.
The German anthropologist Svänte Paabo and his colleagues first deciphered the Neanderthal and Denisovan genomes and showed where and when they interbred with modern humans.
The fossil record indicates that those ancient pre-human people apparently left Africa some 400,000 years ago and roamed across Europe and Asia until modern humans moved into their Eurasian turf from Africa around 85,000 years ago, and quickly replaced them, Parham said.
Homo sapiens overran the Neanderthals from Northern Europe to Spain, and by 30,000 years ago the Neanderthals were gone. Similarly, humans also overran the Denisovans in Siberia and they disappeared at about the same time.
But some of their genes lived on in humans, Parham’s team reported. They were found in modern people in Europe, Asia and Melanesia, but not found in African people, the researchers said.
The parts of the modern immune system that come from the Neanderthals and Denisovans are known as the HLA histocompatibility complex, a group of protein-creating genes located on chromosome six that help protect humans against assaults by some bacterial infections and viruses, and the rejection of tissue transplants.
“All this tells us a lot about human history,” Parham said. “We didn’t just replace the Neanderthals and Denisovans, we have retained some of them in us. There was a lot of diversity in dealing with the pathogens they faced, and we have that diversity too.”
The report is likely to generate some controversy among geneticists. Montgomery Slatkin, a UC Berkeley geneticist who was on Paabo’s team, commented cautiously.
He called the conclusions “plausible,” largely because the HLA genes from Neanderthals were found in Europeans but not in Africans. As to finding Denisovan genes in modern Europeans, Slatkin said: “I am less convinced of this, although their conclusion is not completely implausible.”
He was more certain about the finding that the Denisovan immune system genes exist in modern Melanesians.
“This evidence is the most convincing”