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Re: Dinosaurs to birds



In article <8f06ebb8.36aabace@aol.com>, Dinogeorge@aol.com writes
>In a message dated 1/24/99 0:35:42 AM EST, jbois@umd5.umd.edu writes:
>
><< Randomness and selection are close to antonymns.  Would you agree that
> artificial selection is not random?  Then on what basis is natural
> selection random?  Is it just because we are too thick to perceive the
> patterns? >>
>
>Artificial selection is by definition not random, but natural selection is
>indeed random. In fact, that's the difference between the two selection
>processes.

...Ahem.  Definitions first, please. Artificial selection by definition
has an intelligent agent doing the selecting. Natural selection doesn't.
Both produce an evolutionary trend, a statistical tendency for certain
alleles to be proportionately more represented in the next generation.
Other factors affect both of these processes, including those that we
can't meaningfully predict. And "randomness" is a word for those
phenomena that we can usefully describe only in the form of probability
distributions. I've just flipped a coin and looked at it; for you, the
chance of it being heads is still 1/2. I *know* the answer and
randomness, chance, isn't a very useful concept for me in describing
this particular phenomenon. Nor would it be if I could analyze every
physical force which affected which way the coin fell. You're not too
thick, you just don't have the information. 

Anyway, it may well be true that damn' great lumps of space crud at
orbital velocity are (for most life forms) not the sort of selective
pressure that their recent ancestors were selected by.  And that the
selective pressures in mass extinctions may be very different to those
operating most of the time, and may wipe out most of the organisms
concerned. But let's get our definitions right; all forms of evolution
include chance, randomness if you prefer, and only our Recent mass
extinction has any artificial component to it. Impacting mountains may
be deeply undesirable, not usefully predictable at present, and
unpredictably different to the ordinary mid-Maastrichtian hassles of
reproduction, but they're still natural. And I find the use of "chance"
in mass extinctions to contrast with "ordinary" selective pressures
confusing at best, irritating at worst.  "Different rules" describes the
situation better. 

Thank you for your attention. Now you can carry on arguing... to better
effect, I hope. 

-- 
Richard Keatinge  homepage http://www.keatinge.demon.co.uk

Chance says something sensible about the unknown.  
Statistics say something sensible about chance.