MadSci Network: Evolution

Re: Logical Problem in evolution?

Date: Fri Sep 17 16:27:42 1999
Posted By: Charles Puckett, Faculty, University Parallel; Division of Natural Sciences, Southern WV Community & Tech. College
Area of science: Evolution
ID: 936174837.Ev

     You are correct that mutations are indead random.  What this means to 
a biologist is that there is no way to predict when, or where in a genome 
they will have an effect.  Just because this is a random process does not 
mean that it operates without bounderies;  a gene that codes for 
hemoglobin will not mutate into one that codes for insulin.  Think of a 
single six-sided die, it is imposible to predict what number will come up 
when you throw that die, but you  know it will be a number between 1 and 
6.  You also mentioned that some traits have no appearent effects.  Again, 
you are correct, there are such things as neutral traits.  What defines a 
trait as useful or not really is a measure of how it affects the ability 
of an organism to reproduce.  This is a term evolutionary biologists 
call 'fitness'.  A trait that causes early death would be considered quite 
detremental; one cannot reproduce once one is dead.  So a lethal gene has 
a very low fitness rating.  I cannot see how having six toes would affect 
weither or not a person can reproduce, so I would have to call six toes a 
neutral trait.  However, when you think about evolution, you have to 
realize that conditions can change.  If for some reason (albeit somewhat 
ridiculous) that human females somehow found men with six toes very 
attractive; so attractive that they would only mate with men with six 
toes, this would cause this particular mutation to become an advantage.  
It also passes that six toe gene into future generations, thus making it 
more common.  Any good book of evolution will include examples of 
the 'founder effect' and of a 'population bottleneck'; these are two other 
ways that an uncommon trait may become common.   
     As for other questions you asked.  I assume by human ancestors, you 
mean apes.  A better way to phase that is:"There is little difference 
between humans, apes, and the animals from which they evolved."  When you 
consider the time scale upon which evolution works, it really hasn't been 
that long sence humans and apes diverged.  Certainly not as long as apes 
diverged from other mammals, mammals from reptile-like creatures, and so 
     The reason there are no "useless" organs is that all organs and 
tissues require energy to maintain.  An organism that spends too much of 
its energy maintaining tissues that don't give much of a return 
probably isn't spending that energy reproducing.  If you don't reproduce, 
you don't send your genes into the next generation, and therefore, 
those "useless" energy consuming organs, and the genes that regulate them, 
don't get passed down, causing them to be less and less common.
    Hope I was able to help.

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