Dear Philip,
I think it is fairly easy to come up with the assumption that in most cases, a
mutation IS disadvantageous. Every living organism on the planet right now has
had millions of years of selection pressure causing it to evolve into its
current form, which on the average of the last few tens or hundreds of
generations is the best adapted for the environment it lives in. A case where
a mutation (a change in an individuals genetic expression) might be
advantageous would be when the environment has changed in a specific way and
the mutation gives the individual an advantage towards that particular change.
So the two need to align in order for the mutation to be advantageous, and
considering the number of environmental changes and, in particular, the number
of possible mutations, the probability of an advantageous mutation is quite
small.
We can illustrate this with the example of Darwin's finches, where a changing
environment (lets say the amount of rainfall) decreases the availability of
small seeds. With each generation of finches, a number of mutations will
occur, but most of these will provide no advantage (such as slightly lighter or
darker pigment, different personality traits, longer or shorter legs). In
fact, the deviation from the standard average is, in most cases,
disadvantageous (i.e. different pigment levels make it stand out in a flock, a
more bold personality may be more dangerous, a more shy one may lead to reduced
food discovery thus lower fitness, etc..). Only the occasional mutation in a
bird causing a heavy bill might be advantageous, but these are probably rare,
and the actual evolutionary change comes rather from selecting individuals with
slightly heavier bills from within the standard range of bills (and over time,
shifting that standard range slightly).
The fact is, if mutation causes a significant change in the expression of a
particular gene and causes a change in say a particular physical attribute, it
is unlikely that any other gene expressions will have been changed to
compensate for this unexpected change. Thus, the individual will not be
capable of effectively using the mutation (and hence why large mutations are
unlikely to have leap-frogged evolution).
It is Dawkins who famously said in his book The Blind Watchmaker: "however many
ways there may be of being alive, it is certain that there are vastly more ways
of being dead".
> From:
> To:
> Date: Tue, 8 Dec 2009 17:44:16 +1100
> CC:
> Subject: [Birding-Aus] Backyard bird feeders driving avian evolution
>
> 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: Re: [Birding-Aus] 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
>
> ===================
>
> ===============================
> www.birding-aus.org
> birding-aus.blogspot.com
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