Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1 6/24/83; site cadovax.UUCP
Path: utzoo!linus!decvax!tektronix!hplabs!sdcrdcf!trwrb!trwrba!cadovax!keithd
From: keithd@cadovax.UUCP (Keith Doyle)
Newsgroups: net.origins
Subject: Re: Innocent Question
Message-ID: <613@cadovax.UUCP>
Date: Fri, 10-May-85 22:57:13 EDT
Article-I.D.: cadovax.613
Posted: Fri May 10 22:57:13 1985
Date-Received: Mon, 10-Jun-85 20:01:25 EDT
References: <1534@aecom.UUCP>
Organization: Contel Cado, Torrance, CA
Lines: 49

[......................]
>I was just wonderin'... If evolution happened in abrupt
>changes, wouldn't two animals have to undergo the same
>(or a similar) change? I mean, if in each step the new
>species can't breed with the old, we would need two of
>the new species in order to get something started. 
>What's the chance that there are two animals, 1 male and
>female, within the general vicinity (close enough so that
>they could find eachother), undergo the same drastic change
>in the same generation?
>-- 
>Micha Berger

Note that 'abrupt' is used as a relative term.  I'll try to use
an example.  Let's say there is a large population of some animal,
and they live in two valleys.  One day, some environmental change
occurs that has two effects, a) it seperates the two valleys from
each other, thereby dividing the population into two groups, and
b) effects the characteristics of only ONE valley such that the
environment is drastically changed.  At this point, the animals
in the unchanged valley probably tend to continue on as before.
However, the animals in the changed valley may not be used to their
new environment.  Some animals will have characteristics that improve
their chances for survival in this new environment, while others will
die out.  Over time, these new characteristics will be passed to
offspring, eventually producing a entire population that is better
adapted to the new environment than the population in the other valley.
In addition, it is possible that the animals that had these more
useful characteristics also had other characteristics in common.  These
traits too, may tend to become distributed throughout the population.
If by some chance one of these traits affects sexual attraction, then
even if the two populations are combined again for some reason, they
still may tend not to inter-breed.  Over long periods of time, enough
such changes can occur as to make the two populations so different, that
they may no longer be able to interbreed, and/or are effectively differing
species.  Changes in environment, therefore could be a major mechanism,
and, drastic environmental changes may force a portion of a population
to adapt quickly or die out.  When the environment is relatively stable
for long periods of time, populations may tend to stabilize, or only
adapt to their stable environment with minor improvements. 

I hope this helps.  It is a misinterpretation to think that Punctuated
Equilibrium is saying that changes happen overnight.  P.E. postulates
quick adaptations (relatively) followed by longer periods of statis.
'Quick' in terms of evolution is still thousands of years.

Keith Doyle
#  {ucbvax,ihnp4,decvax}!trwrb!cadovax!keithd