Mike,
Some points:
Charles Darwin knew nothing about the mechanism of genetics, beyond that
characters are inherited from parents and that there is a source of
variation that is inherited. We know a lot more now, so it doesn't help
to quote Darwin too closely in this exercise best to look at the more
recent evidence. Darwin developed the ideas and documented the support
by collecting a lot of evidence but he did not know how the mutation
system works.
I hope I'm right to advise that we don't have any evidence whatever that
mutations are "almost always" disadvantageous. That is just a common
assumption based on what evidence I don't know and I suspect impossible
to test. There is no reason to suspect that mutations are "almost
always" disadvantageous. We have no idea how beneficial or not whatever
proportion of mutations are. It may well be possible that mutations are
"almost always" advantageous. Although that is an equally vague and
probably more unlikely description. In many cases a change to a gene
(i.e. a mutation, which is a change to the sequence of nucleotides along
the DVA strand) may have no impact. We know that by virtue of the way
that the three nucleotides code to one amino acid system works, some
changes to DNA do not alter the protein at all (as the different set of
3 bases may code for the same amino acid). Some DNA changes make small
changes to the protein. Some result in total collapse of that protein's
function. If that happens the impact on the organism may be great or
minor it depends entirely on what the function of that protein is and
the result is totally random. Sometimes it can simply mean that the
particular gene does not function, which allows another gene to function
in a different way. And then there are all the variations created by
sexual reproduction and you get increased rate of mixing of
combinations.
You ask: So can you come up with an example of an "occasional
advantageous genetic mutation"? Well yes, the entire existence of life
and all the variation in the animals, plants, fungi, bacteria, etc is
the example that I think answers that question. Except that would appear
to be something more than occasional! There is after all, no other
detailed and developed suggestion that is consistent with and sensibly
explains the existence and variety of life.
Philip
-----Original Message-----
From:
On Behalf Of Michael
Tarburton
Sent: Tuesday, 8 December 2009 8:42 AM
To: Andrew Bell
Cc: ;
Subject: Backyard birdfeeders driving avian evolution
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
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www.birding-aus.org
birding-aus.blogspot.com
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