On 12/5/05, Chuck Grimes <cgrimes at rawbw.com> wrote:
>
> [From somewhere along the `Instinct' thread]:
>
> AFAIK the most parsimonious (unit of reproduction and trait -- germ
> line? -- replication) and hence preferred view is still individual
> selection. ravi
>
> Yes, I agree there is honest debate about this; however, I consider the
> data that supports the idea of group selection compelling. miles
>
> ----------
>
> (I decided I would post this for general information rather than
> address any particular post on the instinct thread. I think I'll
> post another item on the relationship between genotype and phenotype,
> because like the individual v. species selection argument, it comes up a
> lot.)
>
> There are some critical points missing in the discussions on natural
> selection as the basis of evolutionary change. First, this is not an
> either/or debate. Second, natural selection is not a single
> horizontal class of phenomenon. And third, natural selection is not
> the only mode of evolutionary change.
>
> Natural selection can be argued to show effects at several different
> hierarchal levels from individual organisms on up. The reason is that
> natural selection is not a single horizontal class, say that only
> effects individuals, but a hierarchical family of selection classes
> related together by their effects on different levels.
>
> Gould's term Hierarchical Selection, or those selection phenomenon
> which effect groupings, in this case species. above the individual
> organism level are associated with Macroevolution. The natural
> selection class that shows effects at the individual level and below
> are termed Microevolution.
>
> >From Gould's The Structure of Evolutionary Theory:
>
> ``I have long regarded species selection as the most challenging and
> interesting of macroevolutionary phenomena, and the most promising
> centerpiece for macroevolutionary theory. While I continue to espouse
> this view, my rethinking for this chapter has led me to appreciate the
> significant power of two other species-level processes: drives of
> directional speciation as just discussed ... and species drift, the
> higher-level analog of genetic drift. I would now argue that the
> interaction of these three processes sets the distinctive character of
> macroevolution.
>
> As for natural selection at the organismic level, the two major modes
> of species selection operate by different rates of generating daughter
> species (the analog of birth biases in natural selection) and
> differential geological longevity before extinction (the analog of
> death biases in natural selection). At the species level, however, the
> difference between these two modes does not rest upon the same basis
> that distinguishes their analogs at the organismic level.
>
> At the organismal level, natural selection by birth bias works mainly
> upon such `internal' traits as reproductive rate and brood size, and
> often doesn't increase adaption in the conventional sense of
> phenotypic molding to better biomechanical design for local
> environments. For example, an organism gains large selective advantage
> merely by breeding a bit earlier, though nothing else about the
> phenotype need alter...(..referred to..as `selection without
> adaptation'). But natural selection by death bias among organisms
> usually yields phenotypic adaptation for better fit to the ambient
> environment.
>
> At the species level, however, our main concern moves to an
> interesting difference in causal locus. Most cases of selection by
> differential speciation operate by the interaction of an irreducible
> species-level character---some feature of population structure--with
> environment, and therefore represents genuine species selection. After
> all...organisms don't speciate; only populations do. But for selection
> by differential extinction, a higher frequency of cases can probably
> be explained as the simple summation of organismal deaths...for both
> organisms and species die. ...
>
> However, the most interesting of all differences between organismal
> and species selection may lie not in the phenomena themselves, but
> rather in the character of their interaction with the other primary
> modes of evolutionary change: drives, and drift...''
>
> (731p, Chp 8 Species as Individuals in the Hierarchical Theory of
> Selection, The Structure of Evolutionary Theory)
>
> The term natural selection was originally used by Darwin to
> distinguish a natural or non-human cause from human controlled
> selective breeding and culling. In that context, natural selection was
> limited to naturally occurring environmental causes that effected
> birth rates and death death rates among individuals in a species.
>
> CG
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