They key is in the statement "almost always" - ie not always. Although
artificial selection often retains maladaptive characteristics through human
interference, natural selection can be expected to eliminate most
maladaptive mutations quite efficiently while selecting for the occasional
advantageous one. This is the evolutionary process as generally understood.
My understanding is that genetic material is not necessarily lost at all,
expression of genes can be turned off and altered, only to be turned on
again later in descended species - maybe by changes in bits of DNA we don't
conventionally see as genes - it seems we are just beginning to understand a
lot of this and the roll of the so called "junk DNA" - watch this space
over the next ten years!. Genetic evolution is quite conservative, ie it
used and re-uses the same genes, often in new and different ways. I
I don't know where the quote below comes from, but I'm not sure why
enhancing one characteristic "is likely to be at the expense of others" ,
one could just as easily write "is likely to benefit other characteristics".
Evolution through the natural selection of novel mutations and
rearrangements does indeed enhance the richness of the infomation - hence
the diversity of life birds to marvel at. Just wish they 'ld diverged a bit
more at times when struggling to ID those LBJs and waders!
cheers
Andrew
_____
From: Michael Tarburton
Sent: Monday, 7 December 2009 8:21 PM
To: Andrew Bell
Cc: 'Peter Shute'; ; ;
Subject: Backyard birdfeeders driving avian evolution
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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