new start

On Thursday, September 18, 2003, at 02:36 PM, Lucio de Souza Coelho

> On Wednesday 17 September 2003 16:53, Al Globus wrote:
> (...)
>> Apparently it takes about 20 generations for severe selection pressure
>> to change a population. Unfortunately, I can't give references, but
>> I've seen several discussions of different experiments that reached
>> approximately this result.
> (...)
>
> If by "change" you mean "producing new caracteristics by mutation"
> then then
> yes, it would take many generations.
>
> However, if by "change" you mean "changing the frequency of alleles",
> then
> with enough selection/pressure you can get substantial change in even
> ONE
> generation.
>
> For instance, suppose that you have a herd with black sheep and white
> sheep.
> Suppose that, for some reason, you want just black sheep. You know the
> Mendelian rules for determining the colors. Then you'll mate your
> sheep in
> such a way that in the next generation there will be a predominance of
> the
> black color.
>

Most characteristics aren't, excuse the pun, that black and white. One
of the studies I heard about was breeding out aggressiveness towards
humans in, I think, wolves. By only allowing the most docile wolves to
breed, in 20 generations or so they got wolves that were not aggressive
towards humans.

The dinosaurs were destroyed by an asteroid because they weren't
space-faring. It's almost as if Gaia then thought "Well, dinosaurs
worked pretty well, but space-faring is necessary. Maybe I'll should
try mammals this time." Humanity is now developing systems to detect
and deflect asteroids, and could build orbital space colonies to spread
beyond Earth to insure life would survive a planetary catastrophe.

Al Globus
CSC at NASA Ames Research Center
http://www.nas.nasa.gov/~globus/home.html

Views expressed in this email are only my opinions and are not the
position of any organization I'm familiar with.