[Taxacom] Inbreeding, health, and evolution
weakley at bio.unc.edu
Tue Feb 11 21:54:01 CST 2014
Until the last few centuries, most humans lived in small villages isolated considerably from others. Nearly everyone in the village was more-or-less closely related (1st, 2nd or 3rd cousins) and if you reproduced it was by mating with either a very close or moderately close relative. I know this from my own genealogy... :-)
I imagine that is even more true of giraffes -- giraffes mate with giraffes they encounter in their immediate vicinity, and those mates are very likely to be closish kin. Isn't that how we get to having 9 recognized (genetically differentiated) subspecies of Giraffa extant, each with its narrow and distinctive distribution? Inbreeding or linebreeding is part of how we get to allopatric differentiation of species and subspecies via local fixation of alleles -- albeit with the occasional nonviable or deformed result, which evolution "doesn't care much about".
But perhaps zoo populations are an even more extreme case, more like the Hapsburg royals of Europe -- I don't know...
From: taxacom-bounces at mailman.nhm.ku.edu [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Ken Kinman
Sent: Tuesday, February 11, 2014 9:42 PM
To: taxacom at mailman.nhm.ku.edu
Subject: [Taxacom] Inbreeding, health, and evolution
The whole debate over Marius the giraffe, got me thinking again about something I hadn't looked at in many years. Although the risks of inbreeding are real, especially when it is repeated sequentially over several generations, have those risks been overstated (especially in the first or second generation)? If the risk increases from 2% to 4% for first cousins mating, that is an increase of 100%. Yikes!!!??? But is 4% versus 2% something to getting overly excited about, especially in a non-human species like giraffes?
If Marius the giraffe posed an increased risk of health problems in his progeny that was 4% versus 2%, does that even justify eliminating him from breeding (much less killing him outright?). Geneticists might say that this is a 100% increase in risk, but are they statistically exaggerating the risks (not only to other researchers and the public at large, but perhaps in their own minds as well)?
And as those of us who study evolution of species, do we too often overlook how often species arose from the "founder effect"? Many have no doubt resulted from just a few individuals (or even just a single pregnant female) being isolated on an island or isolated area. And in spite of the obvious inbreeding, a new species is created and can even thrive. Why??? Because inbreeding can not only increase the frequency of bad genes, but sometimes can increase the frequency of extremely beneficial genes as well.
If we are to be open-minded scientists, shouldn't we be looking much harder at such potential benefits, and that the religious prohibitions against matings between third, second or even first cousins, may apply in certain cases, but not the extreme risk it is so often made out to be. In many cases, the risk may overall be neither particularly negative or positive. In which case, the preoccupation of geneticists relating to Marius and giraffe populations, may be overly exaggerated. We will never know in the case of Marius since they prejudged this healthy individual as a genetic risk (perhaps ultimately based on statistics which were exaggerated by some scientists, even though it may have not been exaggerated intentionally). Below is a weblink to just one single discussion of such unresolved scientific questions.
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