Natural Selection

Sometimes called micro-evolution natural selection operates on the existing gene pool to select the genes and combinations of genes that

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Natural selection chooses the genes which are best suited to the environment and eliminates the others.  In Darwin's Finches for example, by emphasising the change in beak shape with nice pictures or clip art, not only is the evident change portrayed visibly but consequent loss of genetic diversity is avoided.   Admittedly the loss is small but it is the very reduction which drives natural selection. 

 

When breeding tropical fish for example there is a desire to "fix" a particular strain.  This is done by inbreeding and selecting the individuals that have the desired combination and don't have the other non-desirable combinations.  When that strain becomes true-breeding then the genetic diversity has been reduced.  It is a trade-off that breeders understand.  There are of course disadvantages to inbreeding such as the dangers of inadvertently selecting an undesirable trait.  Labradors for example are liable to have hip problems.  Conscientious breeders of course will have their Lab hip scored before breeding.  Almost all pedigree dogs are liable to some abnormality.  This incidentally is one of the reasons that some advocate mongrels as all round healthier dogs.

 

 

Ironically a small population is more likely to undergo significant natural selection than a large population.  The evolutionary stasis of species either side of the Isthmus of Panama is explained as a result of similar environments (Pacific Ocean and Atlantic Ocean) and because new alleles and genetic combinations that arise in a large gene pool are swamped by the huge numbers of existing alleles - Campbell's "Biology" Third Edition p463