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Re: Question on morphological saltation
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
I was referring to a morphological gradualism in terms of the
Of course people defended it; it was an actual hypothesis of decent.
The major problem with it was the very limited knowledge geographically
as well as poor temporal resolution. 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. 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.
parents. The white variety then progressively displaced the old variety
from the population until reaching fixation. That is a gradual
replacement. Yet, there was a change from brown fur to white fur, and
not between all infinite hues of brown each time lighter. This I called
"morphological saltation", because of not knowing another term.<<<
For example, suppose a mutation created a white bear from brown
You are using the term correctly, but it's not obvious that this is
actually the case. As I mentioned, in some organisms you get very
discontinuous variation like this, but in more circumstances you do
actually get more continuous variation (like from light to dark). You
also can get chances in the pattern of coat colors that are both
continuous (say variation in stripe patterns on zebras) or discrete
(like the presence or absence of stripes in various white tigers). It
_could_ be that polar bears produced a lighter coat thanks to a chance
mutation that caused it to be white, but it's not necessary and there's
not intrinsic reason why the color could not have gotten significantly
lighter over time. Which actually occurred would have to be
established by experiment (in this case a better understanding of the
gene network that determines color value in ursine fur would probably
constrain the options...perhaps this has been done, but if so I am
unaware of the study).
"process x", without having to hypothesize infinite stages of the
developmental histories for the process.<<<
This, I suppose, can also apply to the trait, say, development of
Right, but again, this is a matter of ongoing debate; almost certainly
both types of variation occur, and the question whether one type is
predominant, and what roll selection plays on those characters. Gould
discusses much this same subject in the latter third of his
Magnum-Opus-sized Structure of Evolutionary Theory, although he and I
would not see eye to eye on the subject of which pattern dominates in
the history of life.
So unless I am greatly misunderstanding your request (and if so I
apologize) then you are asking for something that cannot be answered,
because there is debate over which types of variation are more common
in nature, and to what degree selection acts on them.
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From: Augusto Haro <email@example.com>
Cc: VRTPALEO@usc.edu; firstname.lastname@example.org
Sent: Mon, 20 Apr 2009 11:48 am
Subject: Re: Question on morphological saltation
Thanks for the responses. I am not speaking in population terms when
speaking of morphological saltation, this term is used by me (perhaps
incorrectly) in a sense different from that of punctuated equilibrium.
I am not sure if the gradualism in morphological change I referred to
is necessarily related to the observed variation in one moment of the
population history either.