Freethought & Rationalism Archive

luvluv · 10-23-2002, 05:34 PM

I was going back through some of my old magazines and came across an interesting read on Gould in the New Yorker. (It's not in front of me right now, I think it was the issue before last, maybe late September early October).

It suggested that biologist have not taken punctuated equilibrium seriously since the early 80's (If they ever did at all). Apparently gradualism and strict Darwinianism is still the height of orthodoxy.

Is this what you understand to be the case? I could have sworn I've seen scientists support and defend P.E. in other places (even here, though I couldn't swear by it). Is punctuated equilibrium a dead duck?

RufusAtticus · 10-23-2002, 11:27 PM

Quote:

I was going back through some of my old magazines and came across an interesting read on Gould in the New Yorker. (It's not in front of me right now, I think it was the issue before last, maybe late September early October).

Odd coincidence, Wyatt Anderson gave me a copy of that article today for a siminar class around Dobzhansky's book.

Quote:

It suggested that biologist have not taken punctuated equilibrium seriously since the early 80's (If they ever did at all). Apparently gradualism and strict Darwinianism is still the height of orthodoxy.

Well then the author (Orr) is wrong. It seems to me that he has a misconception about PE. As such it is true that that popular misconception isn't taken seriously, but actual PE is.

Quote:

Is punctuated equilibrium a dead duck?

No, it has a lot of evidence for it, as in the results of PE are observed in most fossil species. Futhermore, the PE explaination of these obersevartions doesn't contradict any of the well established mechanisms of evolutionary biology and in fact embraces them.

[ October 24, 2002: Message edited by: RufusAtticus ]

Jack the Bodiless · 10-24-2002, 02:19 AM

Quote:

Apparently gradualism and strict Darwinianism is still the height of orthodoxy.

Darwin himself was not a gradualist. From what he wrote in Origin of Species about sudden far-reaching changes in ecosystems caused by a single event such as the arrival of a new predator, I think he would be an advocate of PE if he was still around.

Gradualism came from Charles Lyell, not Charles Darwin.

luvluv · 10-24-2002, 01:47 PM

Well, now I'm just darn confused. The author a few times spoke as if he himself were a scientist (one time he said something about how he personally believed it, and I then just took it for granted that he must be a scientist himself- bad move on my part).

So punctuated equilibrium is not dead, and evolution does occassionally "jump"? Any examples?

RufusAtticus · 10-24-2002, 02:10 PM

Orr is a scientist.

Vorkosigan · 10-24-2002, 02:13 PM

Quote:

Originally posted by luvluv:
Well, now I'm just darn confused. The author a few times spoke as if he himself were a scientist (one time he said something about how he personally believed it, and I then just took it for granted that he must be a scientist himself- bad move on my part).

So punctuated equilibrium is not dead, and evolution does occassionally "jump"? Any examples?

That depends. How rapid and how geat does evolutionary change have to be in order to be a "jump?" Speciation can happen extremely quickly. For example, since the London Subway was constructed a century ago, a species of mosquito has emerged that lives in it, and no longer mates with its brethren outside the subway. It has speciated. Other examples of speciation in our time are numerous.

PE does not so much refer to "rapid evolution" as it does to evolutionary change that is jerky, composed of periods of stasis punctuated by short periods of rapid change, instead of smooth gradualism.

ps418 · 10-24-2002, 04:01 PM

Here's an example of both gradual and punctuated morphologic changes in a single lineage of foraminifera.

Quote:

Wei, K-Y., and Kennett, J.P., 1988. Phyletic gradualism and punctuated equilibrium in the late Neogene planktonic foraminiferal clade Globoconella. Paleobiology 14, pp. 345-363.

"Substantial geographic coverage in paleontological study is essential in testing evolutionary models of phyletic gradualism and punctuated equilibrium. We present a multivariate morphometric study of the late Neogene planktonic foraminiferal clade Globoconella using specimens from four Deep Sea Drilling Project sites (DSDP 284, 207A, 208, and 588) along a latitudinal traverse in the southwest Pacific" (p. 345).

"The gradual transformation of G. (G.) conomiozea terminalis (a form retaining a keel) into G. (G.) sphericomiozea (a form lacking a keel) occurred during an interval of about 0.2m.y., with all measured morphological variables showing continuous and steady changes. The evolution of the central populations follows the model of phyletic gradualism. In peripheral populations, the origin of the descendent species G. (G.) pliozea from the ancestor G. (G.) conomiozea terminalis occurred very rapidly within an interval of less than 0.01m.y. . . The evolution os the Globoconella clade shows both phyletic gradualism and puncuated equilibrium. These two 'alternative' evolutionary models complement each other rather than being mutually exclusive. Both models are indespensible towards providing a complete picture of the evolution of Globoconella" (p. 345).

"During the interval of geographic isolation, central populations gradually evolved into a new chronospecies, G. sphericomiozea. It took about 0.17m.y. (from 5.14 to 4.97Ma) to transform the whole ancestral population of the highly conical, keeled morphocline (G. conomiozea terminalis) into the descendent subglobular, non-keeled species, G. sphericomiozea. The evolution in the central populations follows the model of phyletic gradualism. In contrast, the peripheral populations rapidly gave rise to a new species, G. pliozea, a form resembling flattened members of the ancestral populations. The origination of G. pliozea is inferred to be an allopatric speciation occurring within an interval of less than 0.01m.y. Following speciation, the new species remained in morphological stasis for about 0.6m.y. . . The evolution of G.pliozea follows the model of punctuated equilibrium" (p. 361).

And here is an example of an evolutionary transition amongst radiolaria, showing both gradual and punctuated aspects:

Quote:

Lazarus, D.B., 1986. Tempo and mode of morphologic evolution near the origin of the radiolarian lineage Pterocanium prismatium. Paleobiology 12, pp. 175-189.

Pterocanium prismatium is a fossil radiolarian lineage commonly found in equatorial sediment cores throughout the world ocean. It first appeared in the fossil record ~4ma, and became extinct 1.8ma. Previous examination of phylogenetic pattern in late Neogene Pterocanium (Lazarus et al. 1985) observed the origin of P. prismatium from P. charybdeum in severak sediment cores from the equatorial Pacific and Indian Oceans. The P. charybdeum lineage is extant today in tropical and subtropical waters, and extends back in time well into the Miocene. The origin of P. prismantium from P. charybdeum thus represents biological speciation, as it involved the splitting of one ancestral lineages into two descendent ones (p. 175).

Morphometric examination of cladogenesis and phyletic evolution in two late Neogene sister lineages of marine microfossils (Pterocanium prismatium and Pterocanium charybdeum, Radiolaria) from two equatorial Pacific sediment cores was undertaken to better understand the rate of cladogenesis and its relation to subsequent phyletic change. The origin of P. prismatium from P. charybdeum ~4ma ago has been estimated to take place over an interval of ~500,000 yr. Results show that the speciation event consists of two distinct phases. The firsst phase, cladogenesis, occurred relatively rapidly (on the order of 50,000 yr). A second phase of relatively rapid divergent phyletic evolution away from the common ancestral state followed in both descendent branches and continued for at least 500,000 yr after completion of the cladogenetic event. Net evolutionary rates over the next 2ma appear to be much slower. Individual characters change by as much as 2 population standard deviations during cladogenesis, and by a total of approximately 3 standard deviations over 2.5ma of phyletic evolution. Up to 5 population standard deviations of change during -50,000 yr of cladogenesis, and 7 additional standard deviations of phyletic change over 500,000 are observed in multivariate (discriminant function) indices of morphologic difference. The measured pattern does not appear to be either strictly 'punctuated' or strictly 'gradual,' but instead shows features of both hypothesis (p. 175).

Xeluan · 10-25-2002, 05:19 AM

Quote:

Originally posted by luvluv:

Is this what you understand to be the case? I could have sworn I've seen scientists support and defend P.E. in other places (even here, though I couldn't swear by it). Is punctuated equilibrium a dead duck?

I suggest two books.

"The Darwin Wars" by Andrew Brown. This book really gets into the various battles and personalities that punctuated evolutionary theory by basically drawingthe battle lines on how much one agreed with Dawkins and Gould.

Though the "The Darwin Wars" is fun and interesting, "Dawkins Vs Gould" by Kim Sterelny is a better, in depth look into the differences between Gould and Dawkins. Very readable as well.

The trouble is that many who should know better equate PE with extreme saltational events (ala the infamous hopeful monster) when Gould and Eldredge never equated PE with such events.

Xeluan

[ October 25, 2002: Message edited by: Xeluan ]

10-23-2002, 05:34 PM	#1
luvluv Veteran Member Join Date: Mar 2002 Location: Planet Lovetron Posts: 3,919	Steven Jay Gould article in the New Yorker I was going back through some of my old magazines and came across an interesting read on Gould in the New Yorker. (It's not in front of me right now, I think it was the issue before last, maybe late September early October). It suggested that biologist have not taken punctuated equilibrium seriously since the early 80's (If they ever did at all). Apparently gradualism and strict Darwinianism is still the height of orthodoxy. Is this what you understand to be the case? I could have sworn I've seen scientists support and defend P.E. in other places (even here, though I couldn't swear by it). Is punctuated equilibrium a dead duck?

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10-24-2002, 01:47 PM	#4
luvluv Veteran Member Join Date: Mar 2002 Location: Planet Lovetron Posts: 3,919	Well, now I'm just darn confused. The author a few times spoke as if he himself were a scientist (one time he said something about how he personally believed it, and I then just took it for granted that he must be a scientist himself- bad move on my part). So punctuated equilibrium is not dead, and evolution does occassionally "jump"? Any examples?

10-24-2002, 02:10 PM	#5
RufusAtticus Veteran Member Join Date: Nov 2001 Location: NCSU Posts: 5,853	Orr is a scientist.

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