Gradualism vs. Puntuated Equilibrium

P

Poincare's Stepchild

Inside a Klein bottle.
Registered Senior Member
I have only been here a few days, so if this has already been covered, forgive me.

I would like to start a debate over Gradualism (the traditional view of evolution, marked by slow, steady change) versus Punctuated Equilibrium (marked by long periods of very little change, interspersed with periods of rapid change).
 
You are forgiven. :D

To get the ball rolling, perhaps you would like to tell us which theory you support and why.....<P>
 
I thought it has been resolved that punctuated equilibrium fits fossil evidence better than gradualism.
 
Well, I don't think anyone is in a position to resolve this issue definitively. Certainly it is my underdstanding that punctuated equilibrium is the favoured theory since the 70's as a result of Eldredge, Gould, Stanley and others.

It is not only the fossil record that can be used to argue the case for punctuated equilibrium. Molecular studies show that ~99% of the DNA of humans and chimpanzees is identical, demonstrating that a small change in DNA could cause large and important morphological changes. Findings in paleontology and molecular biology have prompted scientists to consider seriously the view that mutations in regulatory genes can create large changes in morphology in a relatively short time.

Taken from:
Developmental Biology, 6th Edition
Scott F. Gilbert

SINAUER ASSOCIATES, INC., Publishers,
ISBN 0-87893-243-7<P>
 
Punctuated equilibrium definitely makes sense. During a long period where the environment is pretty much static, once a species has adapted to it, there is likely to be little change, since there is no environmental pressure to drive it.

Now that catastrophism seems to be accepted in geology circles, you have times when the environment changes rapidly, causing rapid change in a species.
 
Im gonna go with punctuated equilibrium.
In my mind, I can picture substantial genetic mutation occuring only after environmental factors dictate the change being necessary.
 
Eflex tha Vybe Scientist said:
Im gonna go with punctuated equilibrium.
In my mind, I can picture substantial genetic mutation occuring only after environmental factors dictate the change being necessary.
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Actually, I believe the mutations are occurring at a fairly constant rate, even during times of environmental stability. However, if they are neutral, or even slightly disadvantageous, in the stable environment, they are not going to be selected by nature and will have little effect on the species.

But if a rapid environmental change occurs that now makes that gene an advantage, it will rapidly move throughout the population. This is why punctuated equilibrium occurs.
 
PE.
and like spurious said, note that PE happens gradually.
The change may be gradual on a human scale, but not a geologic scale. Evidence indicates it happens fairly quickly.
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Gradual doesn't mean slow. Gradual means it happens in small steps. wiki explains it better:
Punctuated equilibrium is often confused with quantum evolution, saltationism, catastrophism, and with the phenomenon of mass extinction, and is therefore mistakenly thought to oppose the concept of gradualism. Though it is actually more appropriately understood as a form of gradualism (in the strict and literal sense of biological continuity). This is because even though the changes are considered to be occurring relatively quickly (relative to the species geological existence), changes are still occurring incrementally, with no great changes from one generation to the next. This can be understood by considering an example: Suppose the average length of a limb on a particular species grows 50 centimeters (20 inches, a large amount) over 70,000 years (a geologically short period of time). If the average generation is seven years, then the given time span corresponds to 10,000 generations. Thus, on average, the limb grows at the minute, gradual rate of only 0.005 cm per generation (= 50 cm/10,000 generations).

from wiki, punctuated equilibrium.


PS.
Note that plants sometimes do NOT speciate gradually. Polyploidy (allopolyploidy and autopolyploidy) can result in new species as fast as from one generation to the next. And the new species can also look very different from the parent one.
 
let's give it a go.

What is gradual anyway? Or punctuated?

Imagine there is a duplication of the HOX cluster. The next generation looks exactly the same. But now there is so much room to play with gene regulation and bodypart determination that we have something like a 'cambrian explosion' in the next few thousands of generations.
 
All I'll say is that there are exceptions to every "rule" (although I don't think anyone is saying it's a rule). It would be incredibly foolish to say that every single species hass evolved through only one way or the other.
That's why I think PE is right. Most of the time I think things are slow and gradual, but sometimes they're fast... yet still gradual... and other times it's neither all that fast nor all that gradual.... and that's ecompassed by PE.
 
Definitions are a bit blurry here. PE and gradualism are not in direct conflict (although Gould sometimes put it like that). In fact, I sometimes think that gradualism was basically a strawman put forth by Gould (and Edredge, I think), to underline their point.

If we talk about speciation we are necessarily talking about populations. So we are not talking about individual changes but rather about the change of allele frequency in the population.

As such the gradual element is for instance the change in allele frequency (e.g. mutation rates), the probability of fixation of new alleles and so on. Given a sufficient large population large scale changes (like split off into new species) are very unlikely. So Gould argues that factors necessary for speciation are for instance geographic isolation coupled with genetic drift. Something which was not a precisely new concept (peripatric speciation, a special case of allopatric speciation).
The evolutionary rate does not change as AlphaWolf pointed out, as such it is not a saltatory evolution. So "punctuated" does not refer to the evolutionary rate, but rather to the point on which speciation can occur, usually coupled with a constraint in gene flow by, as already mentioned, for example geographic isolation.

Or in other words, one has to be careful not to mix up evolution with speciation...
 
spuriousmonkey said:
and the punctuation of speciation is just punctuated because of the human urge to classify and put labels on things?
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You need to keep to the definition of "punctuated equilibrium" in reference to the theory of evolution. As I stated at the start of this thread, PE is marked by long periods of stable environment and very little change in species, interspersed with rapid change in environment and rapid species change.
 
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