Andrew wrote:

[..]

> It seems to me that for there to be a selective effect it does not
> have to be starvation to death but a level of starvation which
> prevents successful reproduction.  Any capacity to reproduce in the
> face of food shortages would be advantagous.

From studies of physical anthro and human variation, Syracuse Univ.
courses:

This is about 'evolution' which might better be understood as
'adaptation'.

Anthropologists identify 4 forces of evolution:
1. mutation
2. natural selection
3. gene flow
4. gene drift

1. Mutation is the rise of genetic changes in a population of a
   species.  These are changes in DNA occuring during meiosis: the
   formation of reproductive cells.

most relevant to this discussion:

2. Natural selection has been known as 'survival of the fittest' but
   might better be considered as differential reproductive success.
   The key here is 'differential'.  If a genetically transmitted
   characteristic allows even a slightly greater number of offspring
   who in turn produce a slightly greater number of offspring that
   characteristic will survive and dominate.  Some characteristic
   might be present in small quantity in a population for many
   generations but rather abruptly increase in frequency due to some
   shift in environment.  An example might be some ability to thrive
   on grain based diet that might respond favorably to a shift from
   h-g subsistence to grain farming.

3. Gene flow is the phenomenon of sharing of genes throughout a large
   area population.  It's the reason that man is exactly 1 species on
   this planet.

4. Gene drift is a sampling error that results from sufficiently long
   total isolation of a part of a species' population from the rest
   of the species.  Random mutation can cause an isolated population
   to change to a different species.  Gene drift would prevent
   sharing of genotype with the rest of the original population.


> immediate question: do these overweight captive animals also suffer
> from diabetes?

Can studies of these animals be made?

> Jennie also wrote:
>
>> It puzzles me that humans could become taller and taller throughout
>> the paleolithic while simultaneously being exposed to fluctuating
>> but significant periods of starvation.  I'd like to hear your
>> comments?

> Adult height is determined both genetically and by childhood
> nutrition so that with increasing nutrition in the western world
> today each generation is taller than the last.

I've seen informal publication drawn apparently from research papers
claiming that increases in height in Japan are due to massive
increases in meat and milk in infant and child diet.