Re: Natural selection vs mutation - in the news

On Jan 26, 1:18 am, Tim Tyler <seemy...@xxxxxxxxxxxxxx> wrote:
Ron O wrote:
On Jan 22, 10:29 pm, Tim Tyler <seemy...@xxxxxxxxxxxxxx> wrote:
Ron O wrote:
On Jan 21, 10:52 pm, Tim Tyler <seemy...@xxxxxxxxxxxxxx> wrote:
Ron O wrote:
On Jan 19, 4:51 pm, Tim Tyler <seemy...@xxxxxxxxxxxxxx> wrote:
New Findings Confirm Darwin's Theory: Evolution Not Random
http://www.sciencedaily.com/releases/2008/01/080118134531.htm

[...]



These guys either rediscovered canalization, or they don't understand
that biological evolution has to build on what came before. Where
else are beneficial phenotypes going to come from? [...]
You mean if not from random mutation? I don't think they
are denying that random mutations exist, merely suggesting
that they do not determine the direction of evolution in
the cases they studied.
Rather like the way brownian motion does not determine
the direction of modern aircraft. [...]
You are just describing the fact that biological evolution has to
build on what it has at the moment. [...]
This thread is not about canalization.

There is a longstanding debate in biology about the significance
of the role of chance in forming observed biological structures.
E.g. see "Chance and Necessity" by Jacques Monod, as reviewed here:

http://dannyreviews.com/h/Chance_and_Necessity.html

To summarise: [...]
So: the issue arises of which /kind/ of explanation to invoke
when faced with the observed features of organisms:
Chance? Or necessity?

The point of this thread is that it reports on experiments
which bear on that issue.

Nope, still canalization, just think about it. You only have a
limited number of avenues to take from a given starting point.
Similar selective conditions will only be able to exploit those
limited ways to go. No mystery.

I /thought/ I had already replied clearly :-|

To use your terminology, from any given starting point
there will be a limited number of directions in which
an organism can develop - due to factors such as
developmental constraints.

However, there may /still/ be choices - about which
evolutionary path species will taken.

The "chance" perspective suggests choices are common -
and that selection plays a relatively minor role
in determining the direction taken - instead,
chance is responsible.

The "necessity" perspective suggests choices are
either rare or that they lead to the same
endpoint - and so don't make much difference
in the long term.

Obviously some combination of these perspectives
is correct, but their relative frequency,
weighting or significance is not obvious -
and the point of this thread is that it
reports on experiments which bear on this issue.

I am puzzeled about why I am having to explain
this repeatedly.

Aren't sci.bio.evolution posters /supposed/ to
understand what the "Chance and Necessity"
issue is about?


Perhaps not. But it might be a good idea if everyone read the article
in question (e-mail me if you want to see "my" copy):

Kiontke et al.
Trends, Stasis, and Drift in the Evolution of Nematode Vulva
Development.
Current Biology 17, 1925-1937, November 20, 2007

--
Joe



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