[ExI] Evolutionary rules was Narrow ecological niches

[Rafal Smigrodzki]

On Sat, Apr 25, 2015 at 12:15 PM, Keith Henson <hkeithhenson at gmail.com>
wrote:

> It is worth keeping in mind general evolutionary principles.
>
> For example, why are people not 2 feet tall or 8 feet?  A few are so
> it lies within the possible.
>
> The short answer is that being either very tall or very short makes
> reproductive success less likely.  If there was an advantage away from
> the current mean, relative reproductive success would rapidly shift
> the mean to where those above and those below the mean suffered
> reduced success to the same degree.
>
> The same applies to every measurable feature of every animal I can
> think of.  That includes intelligence in humans.  It is obvious that
> those below some level of intelligence can't care for children and
> have poor reproductive success.  But it is also clear that the top end
> of the scale must (on average) suffer reduced reproductive success as
> well.


### This assumes that evolution is driven solely by selective pressures on
the frequency of alleles - however, allele frequencies are also impacted by
mutations, and in the case of highly polygenic phenotypes (like
intelligence), the mutational pressures are of paramount importance.

A 4 sigma jump in height in a human can be achieved with a single mutation,
and the phenotype determined by this mutation will then be selected for or
against, with selective pressures determining its spread or disappearance.
On the other hand, a 4 sigma increase intelligence may require the absence
of deleterious mutations in a thousand genes. In this situation, even if
the phenotype is very fit, the offspring may not be as intelligent, simply
because most of them would have a mutation in at least some of the genes.

The increase in Ashkenazi intelligence probably took hundreds of years of
severe selective pressure to achieve a 1 sigma change in verbal IQ. Today a
1 sigma advantage in IQ over average doesn't seem to translate into
significant reproductive success but it was a large boost back when being
poor meant dying childless rather than breeding on welfare. I have no
reason to believe that very high intelligence entails any significant
physiological negative tradeoffs. In fact, the smartest humans tend to be
also the healthiest in general and most socially adept. But it does seem
that being highly intelligent requires a lot of moving parts to work
flawlessly, and thus the entropic forces arrayed against intelligence are
powerful.

Once we transition to mutation-resistant substrates, new vistas for high
intelligence will open.

Rafał
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