GREAT MYTHS OF EVOLUTION #4

by David Menton

IN THE FAMOUS EXAMPLE OF THE PEPPERED MOTH, WE CAN 

ACTUALLY SEE EVOLUTION IN ACTION

The Peppered moth (Biston betularia) is typically a whitish moth

covered with black spots. This coloration provides an effective

camouflage for the moths as they rest on certain Birch trees. Like

humans, however, these moths can be found in a range of pigmentation

from very black to very white and all shades in between.

In a much

touted study in England it was found that when the white trees, on

which the moths rested, became dark from industrial pollution, birds

ate more of the lighter moths (apparently missing the darker ones). It

came as no surprise that the population of darker moths increased while

the lighter ones decreased.

It was further observed (but rarely

mentioned) that when cities cleaned up their air, the trees got lighter

and the lighter moths again predominated. This is clearly natural

selection in action but is this evolution? Not really, unless we call

the natural variation within species that occurs in all plants and

animals "evolution".

The problem with equating this type of variation

with evolution is that it is STRICTLY LIMITED. There are, for example,

over 150 varieties (breeds) of dogs recognized by the AKC and more are

added each year, but they are ALL DOGS (Canis familiaris). You can

select for dogs with long ears or short ears, big dogs or small dogs,

but you can,t select successfully for dogs with wings.

The reason is

simple, there are no genes for wings (and their associated struc-

tures) in the gene pool of the species Canis familiaris. Thus dogs

remain dogs and Peppered moths remain Peppered moths and, as far as we

know, they always have and always will (excepting extinction). One of

the great triumphs of modern genetics has been to explain how it is

possible to have so much variation with in a species with out losing

the distinctiveness of the species itself. This is now known to be do

to multiple alleles in the gene pool of the species.

For many genes of

a species there exists several alternative versions (alleles) though

any individual can have no more than two "versions" of a particular

gene at one time. Thus a person may have eye color genes for blue eyes

or brown eyes, but they are still eyes and both remain Homo sapiens.

IF we were all genetically alike we would be clones! An entire species of

identical twins would not be very interesting but more importantly,

such a population might not survive long in a variable environment. In

conclusion, natural selection among existing alleles is known to

promote the stability and continued survival of a species, but it is

not known to be responsible for why we have come to have people, cows,

dogs, moths, giraffes etc. etc. etc.