I believe you're talking about the theories of Reinhardt Stindl, who
recently published an article in the Journal of Experimental Zoology
Part B: Molecular and Developmental Evolution 302B, 111-120 (2004)
titled "Is telomere erosion a mechanism of species extinction? "
He got a lot of attention for this in non-scientific publications
(even Harper's Monthly ran reference it on the back page of their last
month's issue, I believe), as have a few others for their work on the
burgeoning field of extinction mechanics.
More info on Reinhardt's theories and publications can be found here:
http://www.meduniwien.ac.at/user/telomer/
A nice summary of the current angles on recent extinction debate is on
the Discovery.com website here:
http://dsc.discovery.com/convergence/megabeasts/experts/experts.html
Stindl isn't mentioned in it, but his theories can only lend credence
to the direction Ross MacPhee and others are taking -- that there may
be profound genetic mechanisms governing both speciation and
extinction. MacPhee is interested in the hyperdisease hypothesis and
he outlines it pretty well here:
http://www.amnh.org/exhibitions/expeditions/siberia/hyperbody.html
It's not quite what Stindl is saying, but I'd reckon there could be
connections between the two, I suppose my reckoning comes from a
poorly remembered article by Lynn Margulis about deep-sea viruses, and
the role of viruses in macro-evolution.
In any case it seems to make a lot of common sense that along with
what people think of as "external" factors in extinction (asteroids,
ice ages, one species decimating another) there may be some mechanism
or mechanisms that might "sweep up" a species itself -- the theory of
cellular apoptosis was dramatic and strange when it was first
forwarded, but of course it is accepted fact now; it doesn't seem like
such a great leap to imagine something like that functioning for
entire species, especially if you imagine species as cells or organs
of the body of Gaia.
Two good books on apoptosis are here:
http://biologybooks.net/Apoptosis.html
Most importantly, I believe the answer to your question is:
From the current Guardian UK Article:
"According to Reinhard Stindl, of the Institute of Medical Biology in
Vienna, the answer to this question could lie at the tips of our
chromosomes. In a controversial new theory he suggests that all
eukaryotic species (everything except bacteria and algae) have an
evolutionary "clock" that ticks down through generations to an
eventual extinction date. This clock might help to explain some of the
more puzzling aspects of evolution, but it also overturns current
thinking and even questions the orthodoxy of Darwin's natural
selection"
"Stindl argues that the protective caps on the end of chromosomes,
called telomeres, provide the answer. Like plastic tips on the end of
shoelaces, telomeres prevent instability. However, cells seem to
struggle to copy telomeres properly when they divide, and gradually
the telomeres become shorter. Stindl's suggests that there is a tiny
loss of telomere length between each generations, mirroring the
individual ageing process.
Once a telomere becomes critically short it causes diseases related
to chromosomal instability, or limited tissue regeneration, such as
cancer. "The shortening of telomeres between generations means that
eventually the telomeres become critically short for a particular
species, causing outbreaks of disease and finally a population crash,"
says Stindl. "It could explain the disappearance of a seemingly
successful species, like Neanderthal man, with no need for external
factors such as climate change."
After a population crash there are likely to be isolated groups
remaining. Stindl postulates that inbreeding within these groups could
"reset" the species clock, elongating telomeres and potentially
starting a new species. Studies on mice provide strong evidence to
support this.
David Jablonski, a palaeontologist from the University of Chicago,
says: "The telomere hypothesis is interest ing, but must be tested
against factors like geographic extent, or population size and
variability, that have already been proven effective in predicting
extinction risk." |
