Definition of evolution

James P. H. Fuller jim at crom2.rn.com
Sun Nov 3 11:45:24 EST 1991


In <55093 at netnews.upenn.edu> Frank Yue writes:

> 1) Is it still necessary to refer to our 20/20 hindsight about genetics in the
> definition of a much older concept?

     Concepts such as biological evolution become refined in the light of
accumulating knowledge, and I would not wish to give up this refinement.  That
leaves room for definitions to be neither purely analytical (what do we *al-
ready mean* by X?) nor purely empirical (what *is the case* regarding X?) but
an evolving (heh, heh) combination of the two: what *is there* that we *might
reasonably mean* by X?

     Darwin did not have the benefit of either molecular or Mendelian genetics.
As a result, the very idea of a living species seemed somewhat arbitrary and
unreal to him.  He wrote in the _Origin_:

     I look at the term "species" as one arbitrarily given, for the sake of
     convenience, to a set of individuals closely resembling each other,
     and it does not essentially differ from the term "variety" which is
     given to less distinct and more fluctuating forms.

     By contrast, biologists today generally acknowledge that the term
"species" refers to something objectively real in nature.  It is our knowledge
of population genetics and molecular genetics that so strongly supports this
belief in the usefulness of considering species to be objectively real enti-
ties and not just Lockian "assemblages of ideas" in the minds of taxonomists.

     Since the notion of speciation is so closely bound up the with modern
concept of biological evolution by differential reproductive success, I am
strongly inclined to say that, yes, a good modern definition of evolution
needs to refer to post-Darwinian knowledge of genetics.  If you throw out
the main support for the objective reality of species, you've thrown out
something crucial. 


> 2) Do we want to consider evolution as a positive process that allows a
> population to thrive in its environment better?  If so, then a random 'process
> of change' is not suitable.  I say random, because the process is not oriented
> in the definition.

     The mechanism of differential reproductive success makes biological evolu-
tion "directed" in the sense that it is a nonrandon, more or less accurate
tracking of the changing demands of the environment.  But most biologists 
deny that there is anything directing these changes in environmental demands.
Causing them, certainly.  Directing them, in some occult sense, no.  Thus the
notion of non-directedness creeps right back in to your concept of biological
evolution -- adaptation/speciation/evolution follows the environment, the en-
vironment follows its nose.


> While this definition stuff is going on, let me add some fuel for discussion
> (flaming and arguing, too):
>
> *The human population has come to an evolutionary standstill.*

     Well, if you accept the Gould/Eldridge "punctuated equilibrium" model of
biological evolution, this is just what would be predicted:  lots of evolu-
tionary motion during the original Homo sapiens speciation event, not much
since then, not much expected until the next genus-Homo speciation event,
however that is to be caused.  My personal hope is that it will be caused by
geographical isolation of human populations on other planets, but that's
another story ....


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