Re: Natural Selection - Question

Dave Rindos (arkeo4@uniwa.uwa.edu.au)
Wed, 25 Jan 1995 07:24:10 +0800 (WST)

On 22 Jan 1995, Brian Doyle wrote:

> If a species forces another species into extinction,
> i.e. Humans hunting animals, either by pollution
> or other conventional means, into extinction,
> Is this considered Natural Selection??

If by natural selection you mean Darwinian evolution, then a competetive
extinction of all members of a species does not really fit within the
parameters of the theory. The reason for this is that the central
concept, fitness, is UNDEFINED for inter-specific interactions. This is
true whether the cause of extinction is hunting, disease, or any other
environmental factor (all of these things are part of the ENVIRONMENT of
the species under consideration here). This, however, is not to say that
such factors, when total extinction is not the result, are not potential
factors for natural selection and extinction. And this can go either way
-- human behavious and their (intended *or* unintended) results can HELP
as well as harm the potential success of members of another species
(domestication, of course, is the obvious example here).

Put into other terms: if there is variation in the population which leads
to certain individuals having a greater possibility of surviving in the
face of human intervention (pesticide resistance in insects, for example),
then natural selection IS occurring within that popuation. If, however,
there is NO such variability (such has hopefully been the case with the
cause of small-pox) then we would conclude that the environmental stress
(in this example, vaccination) was too great for the species to handle.
No evolution by means of natural selection occurred, and hence the species
went extinct.

The important thing to remember is that fitness is defined ONLY *WITHIN*
a lineage: it is a common error to say that "species X is more fit than
species Y." You can use the words, but they don't *mean* anything in
terms of evolutionary theory.

Dave

--

	Dave Rindos		  arkeo4@uniwa.uwa.edu.au

    20 Herdsmans Parade    Wembley   WA    6014    AUSTRALIA

    Ph:+61 9 387 6281 (GMT+8)  FAX:+61 9 387 1415 (USEST+13)

      [you may also reach me on rindos@perth.dialix.oz.au]



  Rabbits exist, hence we may speak meaningfully to the evolution of 

     the rabbit.  Some people attempt to study the evolution of 

      human intelligence. We may well have a real problem here.