[ExI] Evolutionary rules was Narrow ecological niches

[Keith Henson]

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.

Of course, as Robin points out, the above situation can be expected to change.

Keith