In the birds the viral fragments were located in "the exact same genomic position," a finding that would be "extremely unlikely" to occur at different times across different species more recently, the researchers noted in their paper. Thus, the hepadnaviruses instead worked their way into common ancestors tens of millions of years ago and has been passed down in the genetic code to new species that evolved in the intervening millennia.
Widening window
As the field of paleovirology has taken off in recent years—thanks in large part to quicker genetic sequencing technology—more and more surprises are emerging from the dark, heretofore little-explored reaches of vertebrate genomes. And Feschotte predicts an increasing number of viral findings in the near future.
"Any kind of viruses can potentially do this as long as they can infect the germ cells," Feschotte says. "This is not going to stop. We're picking the low-hanging fruit right now," he says of viral fossil study. And new research profiling more endogenous viruses is slated to be published soon.
Genetic scans can also provide a new, more even-keeled perspective on viral history, Feschotte says. He notes that the study of virus evolution has likely been subjected to a general selection bias in what strains undergo examination. Most viral subjects have been the cause of modern illness—whether in humans or other organisms. But looking into the genetic past "opens an interesting window, a much less biased window, I would argue, to study viruses," he says.
Feschotte proposes that most viruses that have come under study show such a fast mutation rate because they have recently—in the past thousands of years—crossed over into a new species and "are in their adaptation phase, so it kind of makes sense that we see them evolving much faster." He points to the presence of the Ebola virus, which is relatively new to—and so deadly in—humans, that seems to have existed for far longer in bats and hardly makes them sick. But taking a broader viral history survey can offer a more representative picture of how viruses evolved in and with their hosts.
Malik is not entirely convinced by this interpretation, noting that the unexpectedly slow average mutation rate might have more to do with host genetics than those of the viruses. But many of these uncertainties might be answered with further study in the lab, assessing and even reassembling these extinct viruses.
"These are DNA fossils, and we can always put back together and resurrect extinct species," Feschotte says. "I know it sounds very scary, like science fiction," he adds, "but that can really answer questions in terms of the biology of the virus."
Feschotte explains that other researchers might have to puzzle over fossilized bones and argue indefinitely about whether a hominid walked upright. But with the genetic material of an extinct virus in front of them, researchers can recreate it in the lab. The process (which Malik hastens to note is done "in a highly protected setting") could eventually "reveal to us why these hosts were able to survive and thrive with these insertions," Malik says.
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9 Comments
Add CommentCuriosity killed the cat.
Reply | Report Abuse | Link to thisWouldn't the genetic survival of an endogenous retrovirus depend not only on its ability to replicate (with host assistance), but the ability of the host to replicate, or at least not die too fast? As a result, might not many retrovirus mutations result in death of the host before the retrovirus could be replicated? This might reduce the mutation rate in the host population.
Reply | Report Abuse | Link to thisIf the host exhibits a latent infection it would probably survive unless a change in environment or health caused a shift to a productive infection. With latent, provirus would emerge in offspring.
Reply | Report Abuse | Link to thisThat's the standard process, but the behavior of mutations could be unpredictable.
Reply | Report Abuse | Link to thisAs is in life. All mutations are unpredictible. One thing this does prove is genetic code can be transfered from generation to generation. This might help other research goals in determining alcoholism, addiction behavior that is passed on. These all are in the genome. Great article.
Reply | Report Abuse | Link to thisI think Cédric Feschotte, can close his eyes, toss a dart, and any information he comes up with about viruses will probably be correct. The more exotic you are, the more correct you become. What I have always found interesting in speculating about viruses is; Is the virus rapidly mutating its self so it can live in the host or is the virus rapidly mutating the host and slowly turning the host into a virus so their can be cohabitation? Any time you do anything to living DNA, there is a rapid response and effect. If you could determine if viruses have a gender, wouldn't it be interesting to see what gender virus you have in you?
Reply | Report Abuse | Link to thisInteresting article...parts of it confuse me...if a virus inserts its DNA into the hosts DNA(sperm or egg)...does that mean that its offspring create viruses...not stating this very well...if I have this segment of DNA in my cells passed down to me from my parents...do I create the virus in my cells....
Reply | Report Abuse | Link to thisInteresting article on many levels:
Reply | Report Abuse | Link to this1. The degree to which "infectious agents" (in this case viruses) shape evolutionary change.
2. THe amount of the human or mammalian genome represented by viral DNA.
The fact of the matter is we are dependent upon and evolved to be carriers of a veritible Universe of Microbes: Intelligent Design... um, I think not.
Viral infection usually tends to be a limited acute, non-lethal phase followed by either chronic low-grade infection of viral reproduction or a chronic carrier state. Hepatitis B is a classic example and only a minority eventually succumb to liver failure or hepatic cancer... while many more are carriers.
But on a far more basic level, the human placenta is utterly dependent on viral DNA for normal function! The only difference between us and our primate pals is the degree of invasion of the trophoblastic cells of this hemo-choriol unit (into the uterine decidua)... which allows it to supply the very metabolically demanding, devoloping homo sapien brain. (regulated by our high levels of glycosylated HCG.... but that's not really germane here.)
Anyway, we are all, from plants to animals, apart of this whacky, wonderful evolving Cosmos... so, enjoy the ride and don't be a germaphobe!