Hi Damien,
There is certainly no need for a mutation to be to advantage ONLY or
even mainly if an environment change occurs. Changes to an organism's
genetic makeup can potentially be just as advantageous under a constant
environment, when there is some nuance of the genetic change that gives
some new advantage to the organism to do something new, even in its
current environment. There is no reason to think that everything is
perfect as it is. There are plenty of features in most organisms that
are at best poor compromises that only just survive and would be greatly
aided by some change within its existing environment. A mutation that
creates an ability to never have cancer would almost certainly be of
advantage to any animal, regardless of any change to its environment.
Clearly our species has not had that mutation yet. I don't know if other
species have had it. I would be much better off without an appendix or
nipples or hair growing on the edge of my ears and that has nothing to
do with environmental changes. Those features are there but they are not
there to be of any value. They are simple vestiges, mistakes of history
that our genetic system has not yet had the mutations or the time to
eliminate.
One of the really strange things and great example is to think about the
Cheetah and how it is suffering. Just think of how much better it would
be in coping in its existing environment if it mutated its genetic
makeup to become a social cat or even one that maintained a pair bond.
The mutation to do that clearly has never happened yet, as if it had, it
would give huge benefit to the individuals that had it. As survival
rates for cubs would be much higher.
I don't follow your comment about the finches but I hope you are not
suggesting that the rate of mutation is in some way related to the rate
of environmental change. There are so many value judgements in ideas
about which of those changes help or hinder. There are so many
possibilities that we can't know what proportion are good or bad or
indifferent, whether in a period of environmental change or constancy.
About "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" We know that there are
many genes whose function is to modify the impacts of other genes. So if
one becomes ineffective, the influence of others remains as the
character expressed. There are also many genes that appear to have no
function whatever, they are switched off during the embryology of
animals (most obvious example is in tortoiseshell cats).
I hope I won't feel the need to write any more about this. There are
plenty of books on the subject.
Philip
-----Original Message-----
From: Damien Farine
Sent: Wednesday, 9 December 2009 7:38 AM
To: ;
Cc:
Subject: Backyard bird feeders driving avian evolution
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".
===============================
www.birding-aus.org
birding-aus.blogspot.com
To unsubscribe from this mailing list,
send the message:
unsubscribe
(in the body of the message, with no Subject line)
to:
===============================
|
