[Taxacom] Fwd: Inbreeding, health, and evolution

[Michael Heads]

Hi Ken,

You support founder effect speciation, which was a key premise of modern
synthesis biogeography. But here is what some geneticists have said about
it (fom my 2012 book):

   While many biogeographers have accepted the argument [Mayr on founder
effect and 'genetic revolution'] from genetics, geneticists themselves have
been less convinced. Tokeshi (1999) argued that the genetic founder effect does
not seem to be an effective means of speciation and Nei (2002) cited 'one
of the most important findings in evolutionary biology in recent years:
that speciation by the founder principle may not be very common after all'.
Orr (2005) wrote that despite the early popularity of the idea, 'it is
difficult to point to unambiguous evidence for founder effect speciation,
and the idea has grown controversial'. The experiments of Moya et al.
(1995) failed to corroborate predictions of founder effect speciation and
subsequent studies have also found no evidence for it (Rundle et al., 1998,
Mooers et al., 1999, McKinnon and Rundle, 2002, Rundle, 2003). Crow (2008)
called the idea of genetic revolution 'vague and misguided' (see also Crow,
2009).  Even in birds, founder effects 'may be unnecessary' (Grant, 2001,
cf. Walsh et al., 2005). The passerine *Zosterops* is often cited as the
classic case of a taxon that has evolved by founder speciation (Mayr and
Diamond, 2001), yet a detailed study of clades in the south-west Pacific
concluded that the focus on founder effects in this group 'has been
overemphasized' (Clegg et al., 2002).
   Florin (2001) described how 'The vicariance model of allopatric
speciation has been repeatedly confirmed empirically, while peripatric
[founder effect] speciation has suffered severe criticism for being both
implausible and empirically unsupported'. In her own studies on flies she
found 'no support for speciation through founder effects'. In recent years
the debate has heated up and advocates of dispersal theory have found it
necessary to publish an article stressing 'The reality and importance of
founder speciation in evolution' (Templeton, 2008). This was a reply to
Coyne and Orr's (2004: 401) conclusion that 'there is little evidence for
founder effect speciation'. Coyne (1994) wrote that the idea  'has infected
evolutionary biology with a plague of problematic work'.

Michael



On Wed, Feb 12, 2014 at 3:41 PM, Ken Kinman <kinman at hotmail.com> wrote:

> Dear All,
>         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.
>                     ----------------------------Ken Kinman
>
> http://theconversation.com/birth-defect-risk-for-children-of-first-cousins-is-overstated-15809
>
>
>
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-- 
Dunedin, New Zealand.

My recent books:

*Molecular panbiogeography of the tropics.* 2012. University of California
Press, Berkeley. www.ucpress.edu/book.php?isbn=9780520271968

*Biogeography of Australasia:  A molecular analysis*. 2014. Cambridge
University Press, Cambridge. www.cambridge.org/9781107041028