G'day All who are following this thread that Laurie so kindly brought
to our attention.
Ok I said "almost always" because it is known in science (& hopefully
common sense) that it is very hard in practical terms to exclude
every possibility. ie. to prove something all you have to do is show
that it is true in one or more cases. To disprove something you have
to have investigated all cases - how do you know when you have
achieved that? In many situations you cant so you have to look at
probabilities.
So can you come up with an example of an "occasional advantageous
genetic mutation"? If you cant then this aspect of evolutionary
theory is baseless.
Going back to the original example of the Blackcap Sylvia atricapilla
we can use Darwinian or neo-Darwinian selective theory to explain
that those birds going to the UK instead of Spain would have an
advantage in that they are better fed in winter and have less
distance to return to their breeding grounds. This means they arrive
at the breeding grounds in better condition and earlier than the
birds wintering in Spain. David Lack's research shows this probably
gives them the choice of the best breeding sites and greater success
in producing more offspring than those going to Spain. In time they
will (have?) outnumbered the other portion of their population.
I see no problem with that - and they probably can revert to the
other form if conditions change back (but that varies between
characters) but they are still blackcaps no new genes have been
produced just an advantage to those whose genes allowed them to go to
the UK instead of Spain. This is similar to Biston betularia the
Peppered Moth that was touted in Uni & high school text books ad
nauseam as examples of evolution. Problem is they are still Peppered
Moths and they have started to revert to the lighter form and the
evidence is that they started to do so before the UK started their
clear air program. Problem with that example is that much of the
research has been shown to be faulty & fraudulent. [see Evolutionary
Biology 30: 299-322. The Scientist 13(11):] That has not stopped
some text books still using it.
The examples of Darwin's finches is not too different. Now that good
times have returned to the Galapagos Islands (at least for the
finches) the heavy-billed birds have lost their advantage and are
returning to the narrow-billed form. This is not evidence for the
development of new genes. is is evidence that Darwin's selection
pressures can select for certain genes under certain circumstances.
Nothing new has been created.
So there is good evidence that the environment can selectively favour
certain genes but I am still waiting for just one example of a new
gene having evolved.
Cheers & happy thinking
Mike
===================
Michael Tarburton
===================
On 07/12/2009, at 11:52 PM, Andrew Bell wrote:
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 information - 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!
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