G'day All
Andrew suggested:
"There are many examples of such minor changes in bird populations being
cited as evidence for observable evolution, including melanotic urban
rock
doves. Darwin hypothesised that the development of all species was
due to
the gradual accumulation of just such minor variations over very long
periods of time."
But there is a problem here:
Selective breeding to enhance certain characteristics has long
been common farming practice. Darwin pointed to artificial breeding
such as this in his book On the Origin of Species. He saw it (as many
still do today) as showing that selection can give uphill
improvement, which could eventually lead to totally new creatures.
However, he was unaware that enhancing one characteristic through
selection is likely to be at the expense of others. This is logical,
since selection creates no new information, it only 'chooses' from
what is there. As a variety becomes more specialised through such
selection, it loses some of the genetic richness of its ancestors.
This means that each new variety of dog & pigeon or whatever, has
lost some of the original genome and can never get back to the
original ancestor by selective breeding amongst the same breed.
Though I guess Peter is correct if you let them breed between the
different breeds you would get at least some of the way back to the
original Rock Dove or Wolf. But that is not evolution and actually
demonstrates what I said above about selective breeding actually
selecting some genes and losing others - not making new ones.
To get new genes you need mutations (or at least that is what most
uni texts say), but the problem here is that mutations are almost
always deleterious so that does not support evolutionary processes
either.
So here is to more happy thinking.
Cheers
Mike
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Michael Tarburton
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www.birding-aus.org
birding-aus.blogspot.com
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