How Widely Accepted Is The Theory Of 'Punctuated Equilibrium'?

[Chronos]

Perhaps another example of an equilibrium species: Cockroaches are pretty close to perfect, at what they do. They eat anything, they breed quickly, and they can survive a good deal of trauma. Well, every so often, a roach is hatched which is a little different. This happens all the time, in all species, and sometimes the change is an improvement. But with cockroaches, they’re already so close to perfect that such a change is almost guaranteed to not be an improvement. So evolution favors those bugs which stay exactly as they are.

Now, if the environment of cockroaches were to change suddenly in some dramatic way, then they might no longer be perfect for their environment. Now, it’s possible that a random mutation actually will result in a better-adapted insect, so evolution can act to change them again.

[Cuckoorex]

I’m no biologist, so forgive (and correct) me if I’m wrong here…in Finding Darwin’s God by Kenneth Miller, Miller says that Darwin was in fact describing something very much like the basic premise of PuncEq (I loaned the book to someone, so I don’t have the exact quote); he quoted Darwin as saying that he doesn’t expect that speciation occurs and a steady rate, but that there would be relatively long periods without major changes and then relatively shorter bursts of major changes (in reference to descent with modification)…Miller in the chapter I’m referring to was making the argument that PuncEq does not displace much of anything that Darwin wrote, and that in a way PuncEq looks at larger chunks of geological time than gradualism does…if that makes little or no sense, it’s because I can’t recall the details of the argument entirely…

[Darwin_s_Finch]

Darwin, on divergence of characters:

But I must here remark that I do not suppose that the process ever goes on so regularly as is represented in the diagram, though in itself made somewhat irregular, nor that it goes on continuously; it is far more probable that each form remains for long period unaltered, and then again undergoes modification.

• The Origin of Species, Chap IV, “Natural Selection”

Note that the diagram to which he refers (a facsimile of which can be seen here) represents divergence, but not necessarily speciation through divergence. He later comments:

This gradual increase in number of the species of a group is strictly conformable with the theory; for the species of the same genus, and the genera of the same family, can increase only slowly and progressively; the process of modification and the production of a number of allied forms necessarily being a slow and gradual process, one species first giving rise to two or three varieties, these being slowly converted into species, which in their turn produce by equally slow steps other varieties and species, and so on, like the branching of a great tree from a single stem, till the group becomes large.

• The Origin of Species, Chap XI, “On the slow and successive appearance of new species”

In essence, in Darwin’s view, species diverge in form, and these new forms gradually transform into new species (“these being slowly converted into species”). So, on the one hand, he speaks of divergence of characters occurring much as we now understand speciation itself to occur, but on the other speaks of speciation itself being a slow transformation from these new forms into new species. Many of those who claim that PuncEq is nothing new tend to miss the rather subtle distinction between divergence (which, in Darwin’s view, primarily serves to increase the variation upon which natural selection can act) and true speciation.

Darwin also felt that large populations were more conducive to producing new species (similar to what jsleek alludes):

Finally, I conclude that, although small isolated areas have been in some respects highly favourable for the production of new species, yet that the course of modification will generally have been more rapid on large areas; and what is more important, that the new forms produced on large areas, which already have been victorious over many competitors, will be those that will spread most widely, and will give rise to the greatest number of new varieties and species. They will thus play a more important part in the changing history of the organic world.

This is again at odds with the modern view of Mayr’s (and subsequently, G&E’s) allopatric mode of speciation.

[bryanmcc]

*Originally posted by Colibri *

*Originally posted by bryanmcc *
a) two of the Big Daddies of Evolution (Gould and Richard Dawkins)

**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. **

Just to clarify, I meant that Gould and Dawkins are probably the two evolutionary biologists that most people would have heard of. However, I must take issue with your statement that Dawkins has “much less standing as a serious scientist.” If I’m not mistaken, didn’t he do important work in such areas as the concept of the selfish gene (not so much a theory as a useful way of looking at things), the theory of memes, and the computer modeling of evolutionary concepts? I may be misinformed on his importance, but I will confidently state that nearly all of his books are fascinating and ingrossing, and definitely worth a read.

*Originally posted by bonzer *

*Originally posted by bryanmcc *
a) two of the Big Daddies of Evolution (Gould and Richard Dawkins) quarreled about it a bit

**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. **

Which is what I was referring to when I said that part of the problem comes from “people having different definitions in mind when the speak about ‘Punctuated Equilibrium.’” If I recall my Dawkins correctly, he pretty much said that his issue with PE is that he felt it was set up as a flase dichotomy – it was put up against “gradualism,” which Dawkins felt wasn’t even a position held by anyone. No one prior to Eldredge and Gould believed that evolution plodded along at exact rates; most felt it was perfectly reasonable and to be expected that evolution could speed up or slow down in different circumstances. In a stable environment with a large population and little immigration/emigration, selection pressure will be low and evolution will be slow. In a changing environment, selection pressure will be severe and evolution will procede at a faster pace. This is obvious. Dawkins felt that Gould – or, more specifically, the popular press who reported on Gould – set up a straw man of ignorant biologists which didn’t really exist.

So there were quarrels on semantics and phrasing, and how the mechanisms worked, and which mechanisms were more important, and other small details, but PE is pretty much a standard and obvious part of evolutionary theory. The popular and creationist press, however, sank their teeth into it as if it were a major debate causing a huge rift in evolutionary biology. Anything that even appears to contradict Darwin (and, similarly, Einstein’s relativity) instantly and automatically becomes an almost irresistable draw for the press, even if they have to tweak the facts a little to make the story work.

Sorry my last post was so sloppy and unclear, but I was tired and lazy.

[Colibri]

*Originally posted by bryanmcc *
Just to clarify, I meant that Gould and Dawkins are probably the two evolutionary biologists that most people would have heard of. However, I must take issue with your statement that Dawkins has “much less standing as a serious scientist.” If I’m not mistaken, didn’t he do important work in such areas as the concept of the selfish gene (not so much a theory as a useful way of looking at things), the theory of memes, and the computer modeling of evolutionary concepts? I may be misinformed on his importance, but I will confidently state that nearly all of his books are fascinating and ingrossing, and definitely worth a read.

By “serious scientist” I am referring to the way he is seen in the academic world. Nearly all of Dawkins’ publications, especially over the past 20 years, are non-peer-reviewed (books in particular are not peer-reviewed) and as such not seen to be very rigorous. (Here is Dawkins’ bibliography, although this is certainly incomplete.) I believe Gould published much more in peer-reviewed journals, and his more technical books I think are much more heavily documented than those of Dawkins. I can’t recall ever having seen Dawkins’ work cited in a journal article, whereas I have frequently seen Gould’s.

I’m not saying that Dawkins doesn’t have interesting ideas, but they haven’t been developed with the kind of scientific rigor that Gould’s have.