The Role of Retroviruses in Human Evolution

mhackarbie writes "The current edition of the New Yorker magazine has up a story about endogenous retroviruses in the genomes of humans and other species. Although researchers have known about such non-functional retroviral 'fossils' in the human genome for some time, the large amount of recent genomic data underscores just how pervasive they are, in a compelling tale that involves humans, their primate cousins, and a variety of viral invaders. Some researchers are even bringing back non-functional viral remnants from the dead by fixing their broken genes."

Re:Oh no!

[cpricejones]

Viruses are relatively speaking, very simple. They have very few genes, and they have few functions. By comparison, simple bacteria often have several hundred times as many genes. If we want to understand how organisms work period, it's necessary to start with the basics. I study retrovirus proteins, and our collaborators routinely use "live" HIV viruses to infect cells. The procedures are quite standard. In those experiments, often the HIV strain that is used can only infect cells one time and cannot replicate. The researchers in the article do the same thing.

Re:Hmm

[fm6]

You're not the first to have that thought. It was part of the premise of Greg Bear's SF novel, Darwin's Radio. He, in turn, got the idea from various scientists, cited in the back of the book. (Sorry, no copy at hand.)

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[account_deleted]

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Two SciFi novels I recommend

[ridgecritter]

that have emergence of HERVs at the core of their plotlines are Darwin's Radio and Darwin's Children, by Greg Bear. Good reads, both.

Can you bring a virus back from the dead...

[RichPowers]

If it was never alive in the first place?

Scientists still debate [wikipedia.org] if viruses meet the definition of life as we know it. I'm certainly not qualified to render an opinion on the matter; I just think it's fascinating how viruses occupy this gray area between our definitions of living and non-living.

Here's a PDF of a SciAm article about this very debate [uvm.edu], written by the Director of Virus Research at UC Irvine.

Re:Reactivated retroviruses

[GwaihirBW]

Unfortunately viruses don't compete directly in that potentially harmless way . . . HIV's niche is in your T cells (and others), reproducing itself until the cell explodes. Viruses [wikipedia.org] don't really prey on each other (they are simple RNA injection machines that parasitically use the replication mechanisms of cells they infect for reproduction. The only way for another virus to block it is to just kill all the potential target cells first (not so helpful) or to infect them with counter-RNA that neutralizes that of HIV. The problem with the second is that unless it's also doing dangerous things to you, that helper virus isn't going to be able to spread in order to combat the HIV. It's just not the same as gut bacteria - they take up residence on the limited available real estate, do some digesting of the food you helpfully provide, and defend their turf from unwanted invaders while managing their own reproduction and such, whereas viruses are hijackers by nature.

Re:Cambrian explosion?

[Colin Smith]

Such viruses may be responsible for the Cambrian Explosion.

Or maybe... The big change at the Cambrian was a mutation which allowed the creation of shells and bones.
 

Re:Oh no!

[TriggerFin]

Active viruses aren't typically transmitted as part of a person's DNA, as that would involve an usurped sperm or egg cell. As you imply, those cells don't reproduce themselves, so they don't make good homes for a virus, which would break them anyway. There is fluid exchange involved in reproductive (and most other) sex, and they do get around that way, since they tend to be floating around your body soon after they've gotten into one cell.

These are NOT active viruses, they're leftover bits that got swept up and tossed in the stew pot back when you were a monkey, shrew, fish, bacteria, or whatever. Most of the junk in your DNA has been put to some use, even if just to mark another section as not used. They can be used to trace evolution, by looking to see who's got what bits.

Re:excellent article

[bob19794]

There is a book out this year that seems related to this discussion, called Survival of the Sickest by Sharon Moalem, a medical student with PhD.'s in neurogenetics and evolutionary biology. He writes this book in a conversational style fairly understandable for general audiences. I recall his describing endogenous retroviruses in the human genome and reverse transcriptase as a mechanism. His main argument seems to be that a number of hereditary diseases like sickle cell anemia, diabetes, and hemachromatosis (a problem in regulating iron absorption) are hereditary because they conveyed some advantage to survival in the past, such as resistance to bubonic plague or malaria. He also touches on research in non-coding DNA and transposons ('jumping genes') and epigenetics (on variables affecting whether genes show up actively in the phenotype or remain dormant in the genotype.) I found the book in Orange County Public Library. A website: http://www.survivalofthesickestthebook.com/ [survivalof...hebook.com] has excerpts,reviews, and the author's blog. Johnathan Prince, a professional writer, is listed as co-author, presumably helping to make the book understandable to general readers. That includes me, and I found it fascinating and educational.

Re:Oh no!

[shawb]

Most of the junk in your DNA has been put to some use

Actually, that is pretty much false. About 2% of our DNA does anything to encode for protein. As a reference, the article states that about 8% of our DNA is relegated to fossil viruses (much of this bulk being redundant copies of the same of very similar viruses.)