Re: Article: Retrovirus struck ancestors of chimps and gorillas

From: Guy Hoelzer (hoelzer_at_unr.edu)
Date: 03/04/05 

Date: Fri, 4 Mar 2005 14:43:12 -0500 (EST)

This article strikes me as shockingly naïve, or at least unaware of the
existing literature and current thinking about hominoid evolution. I think
the authors also make implausible (IMHO) and cryptic assumptions, which
guided their speculations about why the remnants of this retrovirus are not
found in human genomes (as far as we know). For example, it seems bizarre
to suggest that the retrovirus infected the ancestors of chimps, gorillas,
and other old world monkeys, but not the ancestors of humans. I don't know
of any physical anthropologists who think it is plausible that the shared
ancestors of apes and old world monkeys were not also ancestors of humans.
It also seems to be a glaring omission not to consider the possibility that
the remnants of the retrovirus may have been lost from the human gene pool
as the result of a deletion.

Guy Hoelzer

in article d0911r$1hj3$1@darwin.ediacara.org, Robert Karl Stonjek at
rstonjek@bigpond.net.au wrote on 3/3/05 11:00 PM:

> Public release date: 28-Feb-2005
> [ Print Article | E-mail Article | Close Window ]
>
> Justin Reedy
>
> Retrovirus struck ancestors of chimps and gorillas millions of years ago,
> but not ancestral humans.
>
> The ancestors of chimpanzees and gorillas were infected with a deadly
> retrovirus about three to four million years ago, but there is no evidence
> it infected ancestors of modern-day humans, according to research by genome
> scientists. The virus struck after humans had split off the evolutionary
> tree from primates, researchers said. The infection may have played a role
> in the evolution of such great apes as chimps and gorillas. The research
> appears in the April issue of the journal Public Library of Science-Biology,
> which is available online on March 1.
>
> Researchers studying portions of the genome containing 'retroelements,' also
> known as junk DNA, found many copies of a gene sequence in the chimp and
> gorilla genome that didn't appear anywhere in the human genome. They
> translated that genome sequence into its corresponding protein, and
> discovered that it was the remnant of a retrovirus, a type of virus that
> copies its genetic information into the host's genome. Evidence suggests
> that the 'retroelement' originated from an external retrovirus that actively
> infected ape species in the past.
>
> "The reason retroviruses are so deadly, at the genetic level, is that they
> have a tremendous potential to mess up a gene and interfere with its
> expression," explained Dr. Evan Eichler, UW associate professor of genome
> sciences and co-author of the study. "That can have negative effects. It's a
> double-whammy: the virus infected and possibly killed off some of the
> population, but also caused genetic errors in survivors. Those errors would
> have later eliminated more of the population."
>
> The virus had invaded the genome in the germline - in sperm or egg cells -
> allowing the sequence to be passed on to future generations. In those
> animals in which the virus was taken up next to or inside a gene - in the
> part of the genome that codes for the most important biological functions -
> the virus had an even stronger effect.
> What researchers don't understand is why the virus affected the ancestors of
> chimps, gorillas, and Old World monkeys, but didn't affect the ancestors of
> humans or of Asian apes like orangutans and gibbons. The infections took
> place independently, and did not originate in a common ancestor of humans
> and apes. The event also took place between three and four million years
> ago, well after the separation of humans from apes. That split is estimated
> to have occurred five to seven million years ago. During that period,
> ancestral humans were likely to be living in the same area of Africa as
> great apes. African apes may have been susceptibile to the virus, or
> ancestral humans and Asian apes may have been resistant to it. Another
> possibility is that some early humans may have carried the virus, but
> eventually died off.
>
> Researchers also don't know the impact the virus had on the primate species
> it did affect. They found many copies of the virus in the genomes of both
> species, but only a tiny fraction of those copies landed in or near a gene,
> where it would have the greatest impact. Other studies have shown that most
> retroviruses typically land near or within genes. This difference may mean
> the animals that had the virus taken up in or near a gene didn't survive
> long. Because of that natural selection, researchers believe that the virus
> may have had major impacts on the formation of the species we now call
> chimps and gorillas. The virus struck when each of the primate groups was
> still an incipient species with widely varying populations.
>
> If the virus had killed off much of the population of both species, it may
> have created what evolutionary biologists call a population bottleneck. This
> much smaller group of surviving animals would then sort out most of its
> genetic variation in relatively fewer generations than would a larger group.
> This would lead to a higher probability of rare genetic variants becoming
> fixed in a short time. Before long, a genetically disparate population,
> possibly with wide variations in morphology, would have emerged, leading to
> today's chimps and gorillas.
>
> ###
> The study's lead authors are Zhaoshi Jiang, a Ph.D. student in Eichler's lab
> at the UW, and Chris Yohn, a technician at Case Western Reserve University
> in Cleveland.
> http://www.eurekalert.org/pub_releases/2005-02/uow-rsa022705.php
>
> Posted by
> Robert Karl Stonjek

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