evoution, nature, and sexual reproduction (was Crinum incompatibility)

ConroeJoe@aol.com ConroeJoe@aol.com
Fri, 11 Jun 2004 15:48:00 PDT
In a message dated 6/11/2004 11:12:28 AM Central Daylight Time, Jamie

> I suppose it's a bit of hen vs
> egg, as to which developed first and lead to the other.  Is it necessary to
> develope apomixis to assure a goodly crop of fruit?  Or was the species at a
> point of evolution that is so advantageous, further evolution would be a
> disadvantage?  Why would nature find an advantage to what is essentially
> cloning?


The questions are legion and, while explored at length, have not been fully 
explained.  One way I interpret the various hypotheses is that natural 
selection (and hence evolution) favors whatever works at the moment.  Thus, a 
particularly successful clone that can reproduce asexually might have a great 
advantage over the short term (10,000 years or 100,000 years).

However, evolution does not know what will happen next, all it can do is work 
with what nature has provided.  So, there can be no breakpoint at which 
"further evolution would be a disadvantage."  Natural selection marches on, and 
therefore so does evolution.  Clonal reproduction, coupled with the ability to 
reproduce through sexual mechanisms, seems useful for many organisms and helps 
guarantee that there will be a next generation.

However, some animals that practice clonal reproduction (it is called 
parenthogenesis in animals) are presumed to be dead ends.  An interesting example is 
the New Mexico Whiptail Lizard (Cnemidophorus neomexicanus), it is a hybrid 
species from 2 other Whiptail species.  The New Mexico Whiptail is a species 
composed only of females, all the females reproduce by parthenogenesis.   
Additionally, all the females are (essentially) clones of each other.  Actually, 
there are multiple different species of parthenogenic Whiptail Lizards--all are 
considered dead ends--they will have no surviving descendants given long enough 
time periods.  

It is clear that natural selection has allowed the all-female species to 
proliferate for the time being.  But, one thing is also clear; evolutionary theory 
predicts that reproduction without genetic recombination (i.e., sex) will 
lead to eventual extinction.  This is because the environment always changes with 
enough time, and organisms that cannot change will die out; adapt or die is 
the maxim of evolution.  That is why life forms today are very different from 
most forms on the planet 500 million years ago--the time span is long but 
mutation and recombining of genes (some from mom and some from dad) are thought to 
be necessary over such long time scales.  

LINK:  Parthenogenesis (from Wikipedia)

LINK:  About Whiptail Lizards

LINK:  EvoWiki (Evolution Wikipedia)



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