[ExI] IQ and beauty

[rex]

rex <rex at nosyntax.net> [2015-10-09 01:17]:
> I suspect extinctions due to runaway exaggerated traits are also
> rare. So far, not a single example has been presented. A quick search
> didn't turn up any examples, but it did reveal an example where sexual
> dimorphism "improved the carrying capacity of the environment, and thus
> presumably population viability."
> 
> http://www.kokkonuts.org/wp-content/uploads/Sexy2die4.pdf
> 
> [Full text at above URL]

More from the above paper:

Trade-offs between viability and male traits: Did the Irish elk go
extinct because of its antlers?

Megaloceros giganteus, the ‘Irish elkʼ, has been extinct for about 10
000 years (Moen et al. 1999). Adult males grew the largest antlers —
up to 40 kg — of any extinct or extant cervid (Gould 1974). A popular
image is that the antlers simply grew too large for the animals to be
viable: OʼRouke (1970: p. 111) speculates that extinction may have
been ‘the result of the excessive size of the antlers which made it
difficult for the animals to feedʼ. To this date, such speculation
remains popular: a characteristic anonymous web page
(http://www.ucmp.berkeley.edu/mammal/artio/irishelk.html) states that
‘the Irish elk finally went extinct when the antlers became so large
that the animals could no longer hold up their heads, or got entangled
in the trees.ʼ Somewhat more scientifically, Moen et al. (1999)
estimated the energetic requirements for antler growth in this species
and suggest that an inability to evolve smaller antlers quickly enough
during a climate change event 10 600 years ago contributed to the
extinction of the species. Gould (1974) likewise suggests that the
antlers became a too heavy burden in this climatic and habitat change.

There is little doubt that adaptations that improve a maleʼs mating
success can be detrimental to his survival (Promislow 1992, Promislow
et al. 1992, Owens & Bennett 1994, Moore & Wilson 2002). This applies
both to ‘armamentsʼ used in male-male competition, and to ‘ornamentsʼ
favoured by choosy females. Note that larger traits can be more
detrimental despite the fact that in comparisons between individuals
ornamental traits often correlate with higher viability (de Jong & van
Nordwijk 1992, Jennions et al. 2001). But can these detrimental
effects drive a population extinct?

Consider a polygynous population, where males express a trait that
improves their mating success over other males, but at a cost of
reduced viability. It seems to us that evolutionary suicide —
i.e. deterministic evolution towards extinction in a constant
environment — is impossible in this scenario. Regardless of the
details of the speciesʼ life history, extinction would require that
too few males survive to maturity to fertilize a sufficient number of
females to maintain a viable population. Since we are assuming that
detrimental effects are evident in males only, a male which survives
better than average would in this situation encounter a large number
of surviving females, and virtually no competitors. The cost of being
an inferior competitor must, therefore, diminish and disappear when
surviving males become scarce. Selection must, therefore, favour the
less extreme male genotypes, and it appears impossible to generate a
scenario where males with larger antlers are still selected for when
the lifetime reproductive success of males with large antlers
approaches zero (as required for deterministic extinction to occur.)

[...]

-rex
--
The primary goal in life is to keep existential pain at a sufficient
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