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Re: Question on morphological saltation



2009/4/20  <dinoboygraphics@aol.com>:
>>> I was referring to a morphological gradualism in terms of the
> old-fashioned orthogenetic series of horses, carried to an infinitum of
> intermediate forms (which I suppose nobody defended), without referring
> explicitly to them (and only for simplicity neglecting ramifications).<<<
>
> Of course people defended it; it was an actual hypothesis of decent.

Admitting infinite intermediate morphological stages? I know they
defended gradual change, but not to that extreme, which was what I was
pointing to.

> That said, it seems to me you are very much
> talking about Punctuated Equilibrium, as many workers do not think that
> macroevolution is significantly different than microevolution except for the
> number of generations involved.

Well, in reality what I ask is more simple than punctuated equilibria
and macroevolution. As far as I understand it, for punctuated
equilibria, you have to speak of fast fixation in small, marginal
populations, and then replacement of the parental species by the
descendant, so as to explain the rapid replacement Gould and Eldredge
claimed to see in their studies.

I am not messing with the rate of the population replacement of the
different varieties, or the replacement of a parental species by the
daughter, or with the presence or absence of stasis, which are
important parts of the punctuated equilibrium model. I am neither
daring to mess with macroevolution regarding novelties, or "hopeful
monsters".

I see in reality two different kinds of "gradualisms" here, which I
think are sometimes confused, which can be related but not necessarily
so:

-one "gradualism" relates to replacement of a variety by other. If I
do not remember wrong, this is what Gould calls "phyletic gradualism".
So, a new variety at first is a small proportion of the population,
then becomes a greater proportion of the population, in a gradual
replacement process, and then reaches fixation.

-the other "gradualism" is morphological, and can be treated
independently from that related to population genetics (and to this,
morphological only problem I refer). This gradualism implies there are
many progressively morphologies each time more similar to the end
result, regardless of populations. For example, in the video of the
transformation of Michael Jackson's face, all the photograms would
represent the intermediate morphological stages. The photograms are
not infinite, but I think it serves to explain the idea. On the other
hand, there seems to be an infinite number of instantaneous
morphologies along the ontogeny of all of us (this is only intended
for explanation).

> You seem to be asking what the smallest
> amount of change between species is, and as evolutionary biologists are
> still disagreeing as to what the dominant pattern of selection, stasis, and
> speciation is, your question cannot even begin to be answered at this time.

Sorry about my explanation difficulties, but my question is not that.
It is: did somebody on a paper (preferrably recent) explicitly wrote
that there do not need to be infinite intermediate morphological
stages between an ancestral and a descendant morphology? And: did
somebody on a paper (preferrably recent) explicitly wrote that
morphological changes have necessarily to be gradual?

It was not my intention to say which was the case for white bears, if
saltation from brown to white or with a number of intermediate hues,
which I do not know. I used they as an example that I was not talking
about gradualism in the sense of gradual replacement of a variety by
another in population terms.

I am not favoring punctuated equilibrium over phyletic gradualism. I
just think that what I called "morphological gradualism" cannot be
entirely gradual, in the sense of infinite intermediate morphological
stages (unlike the ontogeny of an individual). And would like to know
if somebody stated this in a paper.

Thank you Scott for the advise.