Re: dinosaur copulation?

[Derek Tearne <derek@nezsdc.fujitsu.co.nz>]

> 
> 
> >swf@elsegundoca.ncr.com wrote:
> 
> >What would the selective advantage be of growing to such large size
> >after reproductive age?  Remember, natural selection deals in
> >*reproduction* only.  An extreme adaptation can only evolve if it
> >improves *reproduction*.  Thus, a non-reproductive gigantic post-
> >adult would nt be selected for under most circumstaances.
> 
> And yet, somehow, humans have _evolved_ so that their individual lifetimes
> _do_ exceed their reproductive lifetime, as least as far as the female half
> goes - and, considering the ramp-down in libido, etc, with advancing age,
> arguably in males as well.  

Humans have not _evolved_ into this situation.  It has been brought about 
by both an extended family where the old are cared for and by advances 
in nutrition and public health.  The natural life span of a human in 
either a jungle or other similar environment is around 40 to 50 years, 
which corresponds remarkably closely to the reproductive life span
of females.  

Life expectancies of modern peoples ion third world countries fit 
very closely to this age breakdown.

Country       Male             Demale
Algeria        56               58
Burkino Faso   41               44
Mali           41               43
Nigeria        41               44
Senegal        41               44

As opposed to

Australia      71               78
Britain        69               75
USA            70               78

This looks much more like social and economic change than any evolutionary 
change.  I'm sure that a graph of life expectancy against time would show a 
trend for Europe from the low forties to the seventies over a less than a
thousand year period.

I would expect that preagricultural societies would have life expectancies in
the late thirties.

> the creature is very social - in humans, it obviously was an advantage for
> a mother to stop having babies at an age when she was still capable of helping
> provide for her children and grandchildren, possibly because she was then
> removed from the dangers of childbirth and thereafter able to bridge survival
> information to a wider generation band.  

The historical evidence suggests that women essentially continued having 
babies until they died and that other members of the group then looked 
after them.


---
Derek Tearne.   --   derek@fujitsu.co.nz   --    Fujitsu New Zealand   --
Some of the more environmentally aware dinosaurs were worried about the
consequences of an accident with the new Iridium enriched fusion reactor.
"If it goes off only the cockroaches and mammals will survive..." they said.