September 12, 2006 | David F. Coppedge

Do Mammals Depend on Virus Help?

Researchers found that sheep depend on a retrovirus to become pregnant.  Retroviruses (those that can insert themselves into a genome of a host cell) include the dreaded HIV and generally have a bad reputation.  Remnant retroviruses are prevalent in many animal species and have been considered a class of “junk DNA,” having mutated away their ability to cause infection.
    Science Daily, however, reported on research that shows that “naturally occurring endogenous retroviruses are required for pregnancy in sheep.”  A certain class of retrovirus, enJSRV, is critical for formation of the placenta – without it, embryos cannot implant and are miscarried.  Other retroviruses, rather than causing disease, may be essential for protection from infection, the article said.
    How could such cooperation between virus and host evolve?  An evolutionary explanation was included in the article:

Further, Palmarini said, “The enJSRVs arose from ancient infections of small ruminants during their evolution,” said Dr. Massimo Palmarini, a virologist at The University of Glasgow Veterinary School.  “This infection was beneficial to the host and was then positively selected for during evolution.  In other words, animals with enJSRVs were better equipped than those without.  Therefore, enJSRVs became a permanent part of the sheep genome and, in these days, sheep can’t do without them.”

Yet this seems merely a post-hoc speculation rather than a testable hypothesis.  Perhaps there is more cooperation going on between mammals and their tag-alongs than previously realized.

Palmarini ought to read what Jerry Coyne wrote about evolutionary theory (08/30/2006).  Evolution neither predicted nor expected this surprising discovery.  The explanation resembles the habit of Kruschev-era communists to spin every political and economic observation, no matter how contradictory, into terms of class conflict and dialectical materialism.
    If you think back to the commercials of the Leave-it-to-Beaver era, all germs were considered evil.  Wondrous kitchen products like Lysol helped the modern homemaker destroy the wretched bugs and keep the kitchen shining spic-and-span and germ-free.  It is becoming apparent now, by contrast, that most bacteria are beneficial to humans (see 08/02/2006 entry), and that the world is teeming with more viruses than previously conceived, most of which are harmless.  This does not mean we should give up cleanliness and hygiene, but it means that we need to rethink our view of natural evil.  A new view seems to be emerging that life not only tolerates, but may ultimately depend on, bacteria and viruses.
    The relatively small number that cause disease and harm, like brats in the playground, steal most of our attention.  What if the bratty germs are really beneficial players gone awry?  That would fit a Biblical creation model.  A design-based research program could investigate the beneficial interactions of animals with their micropartners and retroviruses, instead of giving up and spraying the “junk” with evolutionary LiesAll.

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Categories: Genetics, Mammals

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