Danny Yee >> Anthropology

Definition of Evolution

To: anthro-l
From: Danny Yee (danny@staff.cs.su.oz.au)
Date: 17 May 1994 15:11:06 +1000

Dwight Read asked:

What is the definition of an "evolutionary process?"
Dave Rindos replied:
That's pretty easy. An evolutionary process, or better said, a Darwinian evolutionary process (in contradistinction to the bad guys' evolutionary theories) is pretty much based upon three suppositions (or observations, if you will):

1) Hereditability of traits

Were traits not reliably passed between generations we could not have evolution.

2) Random (or better said "undirected") variation

If variation were in fact generated to "solve" problems, then Darwinian evolution would NOT occur. It would be truly Lamarkian.

3) Differential spread of traits over time (fitness)

This is more of a CONSEQUENCE of the first two than any special property of Darwinism. If traits are variable, and if new traits arise in an undirected manner (and presuming the obvious fact that traits have some sort of influence on or in the phenotype) then those traits leading to increased relative reproduction OR when certain traits are more successful in being propagated by whatever means, then the traits of the larger population will change over time.

As Dave Rindos already knows, I disagree with this definition. He equates evolution with Darwinian selection, while I think selectionism is just one possible mechanism for evolutionary change. So it is not *definitionally* true that evolution is non-Lamarckian - that it is was the most important discovery of evolutionary biology.

The term 'evolution' was used before Darwin, and is still used by physicists for such things as 'stellar evolution' and 'the evolution of quantum states'. I believe something can be said to 'evolve' if

A) it maintains causal continuity over time (ie preserves an 'identity')

B) is delineated from its enivronment by causal barriers (within the domain in question).

C) is 'connected' (again within the domain in question)

So I would argue that species (gene pools) evolve because they maintain an identity over time (mostly because genes replicate accurately, but repetition of the right developmental conditions may be important to), are separated from other species by barriers to gene flow (cf. Mayr's Biological Species Concept) and are connected by gene flow (cf. Recognition definition of species). [ The essay by Templeton in _Speciation and its Consequences_, edited Otte and Endler, is a good thing to read on species definitions. ]

Biological evolution has one attribute which (I believe) is not necessary for 'evolution', but which is often assumed to be: discreteness in both space (genes) and time (generations). I believe this discreteness is necessary for Darwinian selection to apply.

[ And yes, bricks can be said evolve with my definition; that their evolution isn't interesting is a fact about bricks, not something that can be deduced a priori. :-]

Danny Yee.

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