Tuesday, July 19, 2005
Unnatural Selection
(via Rajan) The Guardian reports on how poaching is changing the gene pool of the Asian Elephant:
(Nitpick Alert) It seems to me that one doesn't have to invoke natural selection to explain Prof Li's observation; a horrendously high poaching rate could also do the trick. For example, if a herd starts out with 5% genetically tuskless males, and 50% of the tusked males are subsequently killed by poachers, then 10% of the remaining population would appear to be genetically tuskless. Of course, if the 10% tuskless ratio referred, not to observed herd populations, but to newborn males instead, then that would indeed be proof of evolution in action. (Unfortunately, the Guardian article doesn't go into detail about this, and I was unable to find the primary research). But I'm skeptical; large-scale poaching has simply not been in action long enough for natural selection to kick in. (End Nitpick Alert).
Either way, it's a terrible thing.
Male elephants usually grow tusks, but typically around 2%-5% have a genetic quirk that means they remain tuskless. By killing elephants for their ivory, poachers make it more likely that tuskless elephants will mate and pass on the quirk to the next generation. Zhang Li, a zoologist at Beijing Normal University and a member of the World Conservation Union's Asian elephant specialist group, studied herds in China and found that up to 10% were tuskless.
The illegal trade in ivory has also skewed the sex ratio of the elephants in China, with females now outnumbering the males by four to one.
(Nitpick Alert) It seems to me that one doesn't have to invoke natural selection to explain Prof Li's observation; a horrendously high poaching rate could also do the trick. For example, if a herd starts out with 5% genetically tuskless males, and 50% of the tusked males are subsequently killed by poachers, then 10% of the remaining population would appear to be genetically tuskless. Of course, if the 10% tuskless ratio referred, not to observed herd populations, but to newborn males instead, then that would indeed be proof of evolution in action. (Unfortunately, the Guardian article doesn't go into detail about this, and I was unable to find the primary research). But I'm skeptical; large-scale poaching has simply not been in action long enough for natural selection to kick in. (End Nitpick Alert).
Either way, it's a terrible thing.
