Gradualism vs. Puntuated Equilibrium

I think that not necessarely, or maybe, not most of the time. I've read sometimes about hybrid viability between species decreasing gradually. (most famous example, of lions and tigers being able yet to sometimes produce hybrid offspring, and sometimes even fertile, despite that lions are more closely related with jaguars and leopards) It may be not as gradual as the evolution of the sum of all other traits, but I think that not much more punctuated than any other trait, in many cases. But will depend on the specific case, I guess.

 

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Tigers and lions do not breed in nature.

 

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About the topic itself. The things, as far as I've read up to now, which may have not been enough, are more or less like this.

First, punctuated equilibrium does not conflicts or "changes" gradualism in any sense. They're not about the same sort of phenomena. There are at least 4 concepts, with two "opposing" pairs, but the pairs are often switched incorrectly.

The "real" conflicts would be gradualism versus saltationism and/or mutationism, and phyletic gradualism versus punctuated equilibria. The "phyletic" is part is often omited, which either lead to or is a result of confusion.

Gradualism, solely would refer to the level of change in one generation to another, and it's very well accepted that most of the time, if not all the time, evolution is gradual. Saltationism, would refer to Robert Goldschmidt's "macromutations", which the precise definition I've never known, and I'm skeptic about all second hand definitions, because they might be a bit of strawmen.

Anyway, in supposing a non-strawman version of the idea (that might not correspond with how Goldschmidt really deffended, I may be "creating" a much more acceptable, weak, version of the concept, supposing the strawmen are "true"), that would be of a more radical change. While gradual variation would be more or less something in the level of the common variation between organisms within a population, variation that we would not point as exceptional in any way, these "leaps" would be just something more odd, that normally, would be expected to be selected against, by being a deviation of the adaptation of the current environment. But nothing like reptiles creating wings all of a sudden, in one generation, if Goldschmidt were not fantasysing so much. I picture just something more odd, more deviant from the holotype than most of the population. As more recently known, I guess that some more drastic changes in hox genes would fit the requirements for that. The mutant wouldn't not be a subtly different variation, within the population, but a "hopeful monster".

If the "monster" is lucky enough to found not be totally unadapted, or better adapted than the "normals", or most preferably/likely, to found a new niche to explore with his difference, that would cause to cladogenesis occur more quickly than what would be normally expected from just gradual variation. And then I think it gets confused with PE.

PE, in the other hand, proposes quicker cladogenesis than phyletic gradualism, but doesn't proposes more drastic levels of change. All the variation needed is the non-exceptional variation present within a population. But as a bigger population is split into minor ones, just by geographical isolation, it solely can make the population evolve quicker, as a matter of population genetics. The populational spliting itself may just randomly generate some difference to begin with, as founder or bottleneck effect. PE then purposes that these random populational events and the subsequent change that would be the main causes of cladogenesis. Short after these populational events, most of the change between the populations would occur, as if "seeking" adaptation, by natural selection, I guess. Once adaptation is reached, it's mantained by selection since the environment doesn't change so much and the species aren't generally highly speciallized. That they call the subsequent evolutive "stasis", a state in which the species is supposed to be in most of its existence.

In phyletic gradualism, the split of populations and subsequent cladogenesis would not be random (in relation with the adaptation), but driven by natural selection. It is usually depicted as being something slower than random split of the populations, but I think that is not necessarely so. That would be more a opposition to PE's stasis than the cladogenesis, I guess, since is often said that is supposed that the species is slowly evolving through all its existence, and barely noticeably spliting in different species.

The lesser known, punctuated gradualism, would be a mixture of both, but I'm not sure if any mixture woud configure that, or if it refers to some specific combination.


Anyway, if these definitions I gave are correct, I guess that all those exist, but with varying frequencies. It may depend on the sort of species we're dealing and their peculiarities. "Saltationism" for instance, I think that would be more likely to occur with arthropods and other groups which, at least intuitively, seem to suport a higher degree of change without compromising the viability or even the adaptation of the organism. In a conciliatory view, that would not be given as done just with the "evolutionary leap", but subsequent natural selection of average variation would likely calibrate the new adaptation.

Nothing impedes, as far as I can see, that both PG and PE/levels of stasis occuring more or less simultaneously, with different traits, since genes segregate independently. While morphological stasis is observed, even more in the fossil record, one can not know in most cases if the stasis is true for other aspects of the organism, besides morphology. The behavior, some aspects of physyology, immunology, could not be in stasis together, but evolving more gradually during the "phyletic segment" in which morphological stasis is observed. Or even evolving more abruptly, as in "evolutionary leaps". The opposite may also be true, some non-morphological aspects may be in stasis (not so much with immunology, I guess), while the morphology is changing gradually over the geological time.

In any case, would not be the question of "which one is true", but of which one is happening or has happened with a species, since both "mecanisms", or "pattern of events" seems very plausible and I can't see no reason why only one of them could occur. I think that the nature of paleontological samples are a bit "biased", tending to lead to the conclusion of morphological stasis, due to the scarcity of samples. In genetics, as far as I heard, things seems to be phyletically gradual in a considerable sort of the time, rather than a boring, never witnessed deviation of Hardy-Weinberg equilibrium.




Well, that all is what I think I know in the subject, but may be something wrong, and I may have made some confusion. One thing that I noted is that saltationism and quantum evolution were put together rather than quantum evolution and PE, which is what I would think that would be more appropriate. Anyway, I've read that QE "evolved gradually" during its existence (or during G. G. Simpsons existence), so both may be true... but as far as I knew, PE and QE were barely indistinguishable, except that PE make more specific claims, I guess.

 

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Are you referring then to "ecological speciation", instead of "mayerian/physiological" speciation?

Anyway, the apparent fact is that hybridization decreases in viability gradually (in a good part of the time). If the simple split of populations with total ability of generating "hybrid" offspring is what is being considered as speciation, than that would be in a considerable part of the time punctuated, I guess. Except in cases which a larger population is gradually separated by some environmental change more or less in the middle of it. If speciation is said to be the inability to produce fertile hybrids, it's apparently more gradual than the geographical/adaptative obstacles on the occurrence of hybrids.

 

IIRC, the "PE is saltationist" and "PE is anti-Darwinian" memes were an invention of the media looking for a good evolution contraversy when the Religious Right was starting to try to push thier crap into the biology curriculum of schools in the 80's.

PE is a natural outgrowth of Mayr's concept of peripatric speciation and also a result of paleontologists getting fed up with the "all apparent sudden (on a geologic scale, a few tens of thousands of years) changes in the fossile record was the result of inperfections in the record" circular reasoning. basically, PE is the result of the genetic drift and rapid spread of "good" mutations that is allowed in small, isolated populations.

 

Danniel, it's not often I see this term brought up in this debate, I usually bring it up though.
I was going to reply to the OP that where Gould sees Punctuated Equilibrum, Dawkins would see Punctuated Gradualism.

Punk Eek = periods of stasis punctuated by periods of change.

Punk Grad = periods of change punctuated by periods of stasis.

Now let's play spot the difference.

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