orthogenesis

[John Grehan]

Without further clarification I could not comment on how Ken could
envisage orthogenesis as some kind of natural selection, but the other
question of their relative importance is something that has been given
some consideration - although it may depend on how one looks at the
situation. Croizat regarded orthogenesis as primary in the sense that
orthogenetic processes determined the 'type of organization' whereas
natural selection only acts with respect to specific environments as a
modifier of local adaptation. On the other hand some theorists such as
Russell Gray have proposed a reciprocal co-construction process whereby
'internal' and 'external' constraints work in concert. Gabriel Dover has
suggested that there are at least two mechanisms to create an
'improbable' shift in genetic makeup - molecular drive and natural
selection, and again he considers a co-evolution. 

I am inclined to see the situation in both the context of Croizat as
well as Gray and Dover even if that may seem contradictory. If I may use
an analogy (which can be horribly misleading in their own right) I see
the Darwinian selection model as a moving train where it is the
environment that is on the move - it is active, while the organism is
basically a passive, static blob of jelly until run over by the train.
In an orthogenetic universe there are two moving trains - the organic
train, and environment train, both moving and intersecting at the same
time and it is at this intersection where we get concerted evolution.
Perhaps I will regret that analogy. Perhaps it obscures rather than
clarifies. And perhaps it is wrong.

John Grehan

> -----Original Message-----
> From: Taxacom Discussion List [mailto:TAXACOM at LISTSERV.NHM.KU.EDU] On
> Behalf Of Ken Kinman
> Sent: Thursday, May 19, 2005 9:47 PM
> To: TAXACOM at LISTSERV.NHM.KU.EDU
> Subject: Re: [TAXACOM] orthogenesis
> 
> I'm reluctant to get into a semantic debate, but couldn't orthogenesis
be
> regarded as a form of natural selection?  And even if you do separate
> them, it seems ill-advised to regard one as being of primary
importance
> and the other of secondary importance for ALL evolutionary trends.
>    ---Ken Kinman
> 
> ***************************************************
> John wrote:
>    7. Orthogenetic development (phylogenetic constraint by molecular
> drive) is of primary importance in evolution.
> 
>    8. Natural selection is of secondary importance, pruning but not
> creating evolutionary trends.