Re: Question on morphological saltation

[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.  
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.

> > > For example, suppose a mutation created a white bear from brown 
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.<<<

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).

> > > This, I suppose, can also apply to the trait, say, development of 
"process x", without having to hypothesize infinite stages of the 
developmental histories for the process.<<<

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.

Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3466 ext. 230
Cell: (307) 921-8333

www.skeletaldrawing.com

-----Original Message-----
From: Augusto Haro <augustoharo@gmail.com>
To: dinoboygraphics@aol.com
Cc: VRTPALEO@usc.edu; dinosaur@usc.edu
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.