Is Stephen Jay Gould’s theory of ‘Punctuated Equilibrium’ widely accepted by biologists as a scientifically sound challenge to Darwin’s theory for the evolutionary process, or is it a pseudo-scientific theory put forward with little or no evidence behind it by some windbag who wanted to make a name for himself by overturning Darwin? What is the consensus among biologists??
Thanks.
Calls for a consensus don’t make good GQ’s.
Suggesting the theory of punctuated equilibrium challenges Darwin’s evolution rather than refines and qualifies it is incorrect.
Making statements that Gould is pseudo-scientific are a windbag is disingenuous, even in question form.
Biologists hold that PE amends the theory of evolution. It does not entirely replace gradualism, rather, PE supplements gradualism. These two are not mutually exclusive.
The consensus among this wanna-be biologist is that you apparently do not understand what PuncEq is if you think it challenges Darwinian evolution.
It’s a statement about the mode of speciation, not an alternate mechanism. Darwin was a strict gradualist, who believed that speciation occurred primarily through the transformation of lineages, and that the splitting of lineages merely served to increase overall diversity. As a result, the fossil record appears to be woefully incomplete, since the vast majority of these transformations are not found within.
Gould & Eldredge suggested that perhaps the inadequacy of the fossil record was not the result of gradualistic gaps: speciation occurs by splitting of lineages, rather than by transforming them. This sort of “cladogenesis” (as opposed to Darwin’s “anagenesis”) occurs relatively rapidly, with respect to geological time. Thus, odds are very low of the geological record actually capturing many of these speciation events. As such, the fossil record actually demonstrates the correct pacing of evolution as periods of stasis, punctuated by periods of rapid change. This does not rule out gradualistic changes completely; only that the primary mode of speciation is cladogenesis, rather than anagenesis.
Note that at no point is there a mechanism proposed which runs counter to plain old natural selection. NS still operates as Darwin suggested in PuncEq.
On second thought, it seems that the misperception that punctuated equilibrium differs from evolution is all too common, so I should have explained further.
The debate revolves around whether evolution occurs at a relatively stable rate, or whether organisms remain static for periods of time and occasionally experience more rapid change. In both cases, classically defined evolution is occuring.
Gradual change proponents accept the there are some variations in rate, but that the driving force is the rate at which mutations generally occur.
Punctuated equilibrium proponents believe that without stressors, there is little driving force behind incorporating mutations even though they are occurring. Normally an environmental change will precipitate a much more rapid period of evolution.
Darwin’s Finch- “Note that at no point is there a mechanism proposed which runs counter to plain old natural selection. NS still operates as Darwin suggested in PuncEq.”
You’re right, I guess I misunderstood ‘PuncEq’.
If PuncEq doesn’t run counter to Darwinian natural selection, then why is it so controversial? From what you guys are describing, it sounds like a fairly minor variation on natural selection.
Again, it’s not a variation on natural selection at all. It’s all about pacing, not mechanism.
It’s controversial because there are still Darwinian gradualists out there. Obviously, these folks would disagree that the fossil record records stasis, but rather is simply imperfect on a grand scale.
So long as there are opponents to PuncEq (or gradualism, if you prefer), there will be debate.
Here’s the FAQ on Punctuated Equilibria from talkorigins. It’s a bit technical, but discusses some common misconceptions about the idea.
The controversy is not so much whether punctuated equilibria or phyletic gradualism occur, but their relative importance.
It should be noted that Eldredge and Gould’s theory draws heavily on Ernst Mayr’s concept of allopatric speciation. Based on modern species distributions, Mayr stressed that most speciation events occur mostly in small, isolated populations at the periphery of a species’ range. E&G extended this idea to paleontology, as the reason one does generally find clear speciation events in a single stratigraphic column.
But once the OP is stripped of its misconceptions, a valid question remains: Is the theory of punctuated equilibrium widely accepted? What’s the word?
I have a feeling the answer is going to be more complicated than a simple “yes” or “no”.
As a professional biologist, I would say the answer is definitely yes. Punctuated equilibrium is probably the most widely accepted explanation for the large patterns of macroevolution over long periods of time. Phyletic gradualism may be important, however, in some lineages or in certain circumstances.
Thanks, Colibri.
I haven’t read anything with regard to PE, so I wanted to run it by you people first to see if pursuing it further would be worthwhile.
Thanks!
First, I have to say IANABiologist, I’m an engineer, but this is a topic I’m greatly interested in.
I had never heard of PuncEq before this post, but it seems to make perfect sense. If I understand the opposite (gradualist) point of view, they seem to think that evolution takes place at a somewhat steady rate.
My question is: How do the gradualists account for organisms like dragonflies, ferns, and other species that show up in the fossil record as basically unchanged from ancient times to their present forms?
Problems also arise from people having different definitions in mind when the speak about “Punctuated Equilibrium.” And it seemed like a larger controversy than it was because a) two of the Big Daddies of Evolution (Gould and Richard Dawkins) quarreled about it a bit, and b) Creationists latched onto a seeming rift in the evolutionary community to further their “argument.” I would recommend reading anything by Dawkins. He specifically addresses this topic in, I think, “The Extended Phenotype,” but all of his books are really excellent.
Try this site. I haven’t actually read it, but I found it while searching for stuff and it looks acceptable.
Some possibilities put forth by gradualists include developmental constraints after speciation (thereby limiting the potential for continued change); “adaptive gridlock”, whereby a population is forced into stasis by external constraints, imposed by competing species; and morphological stasis resulting from large population size, whereby the size of the population itself acts to prevent any novel forms from taking a significant foothold and replacing existing ones. Another theory (which relies explicitly on the incompleteness of the fossil record) states that the new forms would only likely be present if they re-invade the ancestral territory. Otherwise, the new form may be missing completely from the fossil record, even if it exists in theory.
I would qualify this a bit. While both Gould and Dawkins were big names in the popularization of particular evolutionary ideas, only Gould had serious chops as a real evolutionary theoretician. Gould wrote both popular books and highly technical and academically well respected tomes, and developed (or helped developed in the case of PE) some novel theories of his own. Dawkins has much less standing as a serious scientist in his own right.
Not quite. Dawkins’ position, as argued in chapter 9 of The Blind Watchmaker, is that PuncEq is a fairly trivial restatement of ideas from Mayr and hence an utterly respectable part of current orthodoxy. To my knowledge (I haven’t got round to The Structure… yet), Gould never specifically addressed this argument explicitly.
Personally, I’m fairly convinced by the view that Gould’s position changes with time. Once upon a time, he probably did believe that he had some sort of replacement for Darwin, but that faded and was replaced by the belief that Darwinism was a very prescient creed; that Darwin had managed to anticipate most of the elaborations. To the former Gould, PunkEq is heresy, to the latter, the purest of orthodoxies. And Dawkins would, oddly, actually agree.
Let me give a quite theoretical argument why at least some of the time PE would seem reasonable. Of course, it is entirely consistent with basic idea of evolution and it is not much of an exaggeration to say that Gould worshipped Darwin.
First let me raise a question. Why don’t gazelles and cheetahs evlove to get faster and faster till they approach the speed of light? (Ok, I am exaggerating a bit.) The answer is that they have are probably quite close to the limit of how fast an animal with their body plan can actually run. Besides they have reached, if not an equilibrium state, anyway a steady state and only a major increase in speed will change that. Now suppose there is a major change in the environment such that either the cheetahs suddenly get much faster or a new animal appears that is much faster. What will happen to the gazelles? Well basically one of two things. They will go extinct or they will quickly evolve to run much faster. Chances are that doing so will be disadvantageous in some other way. Their bones will become lighter and more fragile. Or their metabolism will speed up and they require more food. Or the increased speed results in more free radicals and the cancer rate soars. Or… whatever. You should get the idea. You can’t do just one thing. But whatever happens it happens fast in evolutionary terms. Or they get extinct fast. Like when man entered the new world an awful lot of animals got extinct within a few thousand years and the buffalo population exploded. Of course, it might not have been caused by man, but if you believe it was all a coincidence, boy do I have a bridge I would like to sell you. The contrary position is mainly political correctness.
Anyway, the point is that an ecology evolves and reaches a steady state in which it is to no species’ advantage to change or change much. Then there is a sudden environmental change and everything is different and species evolve to match it fast or go extinct.
Mathematically, evolution goes by what is called hill climbing. Imagine a blind man try to find the highest point in a landscape. He feel around and finds a direction in which he can go up and does so. Repeat until there is no up; every direction is down. You are not, of course, at the highest point in the landscape (well, probably not, anyway), but you have reached the top of a hill. And there is no way to go so, after a relatively fast climb up the hill, you stop. You have reached stasis. Now there is an earthquake and the landscape shifts. Your hilltop has become a valley. You start climbing again and fairly quickly reach a new peak. Then stop again. If you could see, you could see a higher hill over there and climb down and up it, but you are blind. Evolution is blind (or so I believe and nearly all biologists would concur and the evidence suggests). And evolution is acting in a very high dimensional landscape, crudely speaking one dimension for each gene. But the basic principle seems sound.
BTW, I don’t think Gould ever expressed it in those terms. That is my take on it.
This has been answered far and beyond my powers to add to them, but I’ve always heard that these species have found their niches. Once a species occupies a niche and is unchallenged by either the environment or other species, it remains status quo. There is no reason to evolve.
I went to Antioch college, where Gould went as an undergrad (he entered when he was 16!). I was there about 10 years later, but some of the same professors were still around. What was interesting is that they had a really open mind about the whole gradualism vs. catastrophism schism. I remember one in particular saying that it was wrong to assume that everything happened gradually. For example, the Decca floods had global consequences. What was important is that the same mechanisms that were around millions of years ago are still around today; i.e., volcanism, erosion, asteroid strikes, continental drift, etc. I always wondered to what degree they influenced Gould.
Antioch is also fairly left wing, so they were comfortable with dialectics. You can think of catastrophism as the thesis, gradualism as the antithesis, and PE as the synthesis.
posted by colibri
>http://www.talkorigins.org/faqs/punc-eq.html
containing the sentence
> Daughter species usually develop in a geographically limited region.
Years ago I read an essay by Gould which stated (rephrased) that a stable environment supports a stable population. A niche has an edge, and within that edge evolution is occurring. If the larger environment is altered, the critters in the edge may find new opportunities in the larger environment.
I may have it confused, but it makes sense to me.