We’ve have been uncovering new and often surprising information about our evolutionary predecessors lately—namely, that we’re all more alike than we thought. About a month ago scientists suggested that early hominids are all the same species. And while Neanderthals aren’t early hominids, they are genetically very similar to Homo sapiens, even to the extent that some have proposed bringing them back from extinction via cloning. Another link between us and our Neanderthal ancestors has been unearthed, a virus that affected their DNA and, it turns out, affects ours too.
Researchers from the U.K. published their findings in Current Biology, building on prior knowledge that viruses can affect our DNA if they become genomic, DNA that is then passed on to our offspring. Scientists have never found a virus-altered strand of DNA that spells troubles for modern humans, until now. The new research also builds upon a discovery from last year that indicates Neanderthal and Denisovan (a cousin of the Neanderthal, thought to have lived about 40,000 years ago) DNA was changed by an ancient retrovirus. They were able to chart the alterations because of viral evidence left in genomic junk sequences (sequences that don’t create proteins and don’t seem to do much at all). That research time found 14 instances of viral evidence and then decided to see if they could match of the 14 to our current DNA. Initially, they couldn’t.
This new research team, however, was successful. They took a closer look at those missing instances and indeed found matches to seven, all in cancer patients. They harvested DNA from 67 cancer patients, and each of those samples contained seven of the Neanderthal and Denisovan virus sequences. The scientists think that a link may exist between people who have this ancient virus in their junk sequences and a susceptibility to cancer. Scientists aren’t willing at this point to definitively state that one causes the other, but it does seem that there is some relationship between the two—or else it’s one hell of a coincidence.
It’s also possible that the other seven retroviruses still exist in modern human junk sequences somewhere, and that they scientists just haven’t found those samples or those people yet. The other seven viral sequences could be linked to other medical problems, so the scientists will continue working.
And while we’re talking about weird DNA, it turns out that a recent study of Denisovan DNA indicates that some of their genes came from an entirely different species of hominids—maybe even one that we haven’t identified yet. Given that the Homos sapiens branched off of Denisovans about 400,000 years ago, at which point Denisovans and Neanderthals had already split, scientists thought that both groups would look equally distinct from humans. It turns out that Neanderthals bear more similarities to modern humans than Denisovans, and that there are some anomalies in Denisovan DNA—namely, that fragments retrieved by archaeologists contain DNA seem much older than others. Scientists believe that Denisovans bred with some other species and inherited some of their DNA.
So there might be another discovery on the horizon, yet another species of early man that had escaped our detection. Certainly, as we continue to learn about our own evolution, we will learn that interspecies breeding was more common than initially thought. While some studies indicate that Neanderthals did not interbreed with humans, others aren’t quite as sure.