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The Origin of Species by Punctuated Equilibria

Creation Evolution Journal
Title: 
The Origin of Species by Punctuated Equilibria
Author(s): 
Frank J. Sonleitner
Volume: 
7
Number: 
1
Quarter: 
Spring
Page(s): 
25–30
Year: 
1987

If you have been reading the recent creationist literature, you might come to the conclusion that the biologists have completely overturned Darwin. Thus, we have Duane Gish saying:

Asimov seems unaware of the current uproar in evolutionary circles incited by those paleontologists who are suggesting radical new evolutionary mechanisms ("punctuated equilibria," Goldschmidt's "hopeful monster" mechanism). . . .[Gish, 1981:85]

Or this news item in the September 22, 1981, issue of Awake!: New Debate Among Evolutionists

For decades, evolutionists have been explaining their theory by the process of natural selection. Now a new breed of evolutionists says that this is all wrong. Natural selection can only account for changes within a single species, they concede, and to use this process to explain the formation of new species "is an imaginative leap that cannot be tested by experiment," reports the Sunday Times of London.

The new theorists favor evolutionary "jumps" as the explanation. However, they "have not explained how they [the jumps] occur—although there is no shortage of speculation," says the report. Regarding the debate, the report adds: "There is vast scope for argument and little hope of agreement in the foreseeable future." Sounds familiar, does it not?

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Even science reporters seem to lend credence to these views. A November 1981 "Nova" television program, entitled "Did Darwin Get It Wrong?" concludes that, yes, Darwin was wrong and modern biologists and paleontologists believe that evolution occurs in instantaneous steps. Francis Hitching does the same thing at greater length in an article, "Was Darwin Wrong?" in the April 1982 issue of Life magazine and in a book, The Neck of the Giraffe: Where Darwin Went Wrong. The Eldredge and Gould (1977) hypothesis of punctuated equilibria figures prominently in such reports. The very name itself, an unfortunate choice of words, implies instant changes or jumps followed by constancy. Does punctuated equilibria deny Darwin?

First of all, what does the punctuated equilibria hypothesis really state? Certainly the account by Eldredge and Gould must be considered authoritative:

The model . . . is based on the allopatric model of speciation. The essence of this model is simply that most morphological change is effected (via normal selection processes) through geographic variation within a species, and that most morphological differences between sister species arose either prior to, during, or right after (e.g., character displacement during initial sympatry) the onset of full genetic isolation. The model does not assert that "large" morphological changes occur in jumps—most morphological parameters are perceived as continuous variables and evolutionary modification of such variables will necessarily be gradual-but rather that evolutionary change takes place more rapidly at certain times during the history of a species than at others.

[Eldredge, 1974]

The fossil record at the species level of detail in a local stratigraphic section will show a species in morphological stasis during most of its existence, perhaps showing minor directional changes, and perhaps followed by ". . . a break with essentially sudden replacement of ancestors with descendents; this break may record the extinction or emigration of a parental species and the immigration of a successful descendent rapidly evolved elsewhere in a small, peripherally isolated population (Gould and Eldredge, 1977). Gould essentially says the same in his article, "Evolution's Erratic Pace" (1977).

How long does speciation take? In other words, how "instantaneous" are the "punctuations"? Gould says hundreds, even thousands of years (1977; 1979). Lewin quotes Gould as saying, "I'd be happy to see speciation taking place over, say, 50,000 years . . . " (1980). Fifty thousand years may be an "instant" in the geological record, but in human terms it is a very long time. In creationist terms, it is five times the age of the universe!

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What are the implications for macroevolution? According to Gould and Eldredge:

The model of punctuated equilibria does not maintain that nothing occurs gradually at any level of evolution. It is a theory about speciation and its deployment in the fossil record. It claims that an important pattern, continuous at higher levels—the "classic" macroevolutionary trend&mdashis a consequence of punctuation in the evolution of species. It does not deny that allopatric speciation occurs gradually in ecological time . . . but only asserts that this scale is a geological microsecond.

[1977; emphasis added]

Thus, for example, mammals evolved gradually from reptiles during the length of the Permian and Triassic periods as the small morphological changes from hundreds of successive speciations accumulated. There is abundant fossil evidence for this kind of slow, gradual change. It is a far cry from the reptile-egg-hatching-a-bird idea of Schindewolf (not Goldschmidt) that the creationists use to describe the punctuated equilibria hypothesis.

This doesn't sound like a radical revision of evolutionary theory. As Gould and Eldredge [1977] further state:

For all the hubbub it engendered, the model of punctuated equilibria is scarcely a revolutionary proposal. As Simpson (1976, p. 5), with his unfailing insight, recognized in three lines (where others have misunderstood in entire papers), our model tries to "clarify and emphasize ideas nascent in previous studies of the synthetic theory."

And it certainly does not discard or contradict Darwinism! Gould also says:

The modern theory of evolution—little more than a contemporary restatement of basic Darwinism—does not require gradual change. In fact, the operation of Darwinian processes should yield exactly what we see in the fossil record. . . . Our model is fully consistent with Darwin's central postulate that natural selection controls evolutionary change. Natural selection requires continuity and intermediacy, for selection must create the fit by steadily increasing the frequency of favorable variants. It does not require exceedingly slow and gradual transformation of entire populations.

[1977]

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The above considerations show that the creationists' depiction of punctuated equilibria is totally inaccurate. Gould complains, "It's so utterly infuriating to find oneself quoted, consciously incorrectly, by creationists. . . . None of this controversy within evolutionary theory should give any comfort, not the slightest iota, to any creationist" (Godfrey, 1981). But perhaps he and Eldredge are partly responsible for these misunderstandings because of the way in which they presented their hypothesis. They contrasted it with phyletic gradualism—a model of "a slow steady shift in the mean phenotypic expression" of entire populations over millions of years" (Eldredge, 1974). They assert that this model was the accepted view among most paleontologists and proponents of the modern synthetic theory of evolution. They also claim that this view is implied in Darwin's writings, although they quickly point out that it is not a necessary consequence of Darwinian theory.

Perhaps many of their paleontological predecessors and colleagues did subscribe to that model, but I don't think it would be correct to say it characterized the views of the leading proponents of the synthetic theory. Templeton and Giddings, in a letter to Science (February 20, 1981, p. 770), assembled the following three exerpts:

. . . and we should expect that the more extraordinary developments of sexual plumage were not due like most characters to a long and even course of evolutionary progress, but to sudden spurts of change. (Fisher, 1958).

Now Haldane (1924) showed that a dominant character causing an increase of 0.1 per cent. in the fitness of its carriers would increase from a frequency of .001 per cent. to one of 99 per cent. in a random mating population in 23,490 generations, and somewhat more rapidly in an inbred population; in fact on a geological time scale, almost explosively. (Haldane, 1937).

A species ordinarily tends to persist for very long periods in a state of equilibrium or at best, very gradual advance under ecological pressures that leave only one restricted niche in which there can be successful competition with other species. Yet such species may all the time, especially if population structure is favorable, carry a head of steam in the form of a store of potential variability that permits very rapid change (the tachytely of Simpson (1944) whenever any major ecologic opportunity offers. . . . (Wright, 1949).

In addition, Simpson wrote: "Some groups have been changed rapidly while others were remaining practically unchanged. The same group is commonly seen to have changed rapidly at some time in its history and slowly or not at all in others" (1950).

In another work, Simpson presents the terms horotely, bradytely, tachytely, and quantum evolution to describe and categorize the wide variation in evolutionary rates (1953). In this same work, he presents a diagram illustrating the patterns of evolutionary change of some characters of the horse lineage (p. 265). Some of the cheek tooth characters show a "phyletic gradualism" pattern, but the foot mechanism shows a decidely "punctuated equilibria" pattern, while size shows a mixture of the two types. Finally, the punctuated equilibria hypothesis itself was first proposed (sans name) by Ernst Mayr (1954; 1963; 1970). Mayr considered it a part of modern neo-Darwinism (Mayr, 1967). Eldredge and Gould contributed the provocative name and thrust it upon the paleontological world. (For Mayr's comments on this, see Goldberg, 1985).

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All the scientists cited above are considered strong proponents of the "classic" synthetic theory of evolution, yet none of them was "hung up" on "phyletic gradualism." But what about the author of the following?

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 periods unaltered, and then again undergoes modification.

Many species when once formed never undergo any further change but become extinct without leaving modified descendents and the periods, during which species have undergone modification, though long as measured by years, have probably been short in comparison with the periods during which they retain the same form. It is the dominant and widely ranging species which vary most frequently and vary most, and varieties are often at first local—both causes rendering the discovery of intermediate links in any one formation less likely. Local varieties will not spread into other and distant regions until they are considerably modified and improved; and when they have spread, and are discovered in a geological formation, they appear as if suddenly created there, and will be simply classed as new species.

The above excerpts describe almost all the elements of the punctuated equilibria hypothesis and even speculate about species selection, a related hypothesis. The only element missing is the explicit identification of the short periods of modification with the periods of speciation or phyletic branching! These excerpts, taken from Charles Darwin's Origin of Species (Modern Library Edition, pp. 89 and 357, respectively), are amazingly parallel to the passages from Gould and Eldredge quoted previously.

Punctuated equilibria is not new or revolutionary; it simply shifts the emphasis among a number of classic evolutionary mechanisms. And it strengthens Darwinism insofar as it better reconciles the synthetic theory with the fossil record. Because variation within species is geographically rather than temporally distributed, one will not be likely to see it in stratigraphic sections which represent only one or a few points in the spatial range of a species (Gould and Eldredge, 1977). The work of Williamson (1981; and summarized in Science, November 6, 1981, p. 645, and Newsweek, December 7, 1981, p. 114), who studied an instance of a fossil record continuous over several million years, appears to be a case of punctuated equilibria in which the short-lived transition forms in the speciation process have been preserved as fossils.

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Afterword

Since this article was written, Eldredge has published a book-length account of the theory of punctuated equilibria entitled Time Frames (Simon and Schuster, 1985).

References

Eldredge, N. 1974. "Testing Evolutionary Hypotheses in Paleontology: A Comment on Makurath and Anderson (1973)." Evolution. 28:3:479-481.

Fisher, R. A. 1958. The Genetical Theory of Natural Selection. 2nd ed. Dover, p. 153.

Gish, D. 1981. "The Genesis War." Science Digest. 89:9:85.

Godfrey, L. R. 1981. "The Flood of Antievolutionism." Natural History. 90:6:4-10. See p. 97.

Goldberg, J. R. 1985. "The Eureka Moment: Ernst Mayr." Science Digest. 93:11:67, 94, 97. See p. 10.

Gould, S. J. 1977. "Evolution's Erratic Pace." Natural History 86:5:12-16.
——. 1979. "A Quahog Is a Quahog." Natural History. 88:7:18-28. See p. 28.

Gould, S. J., and Eldredge, N. 1977. "Punctuated Equilibria: The Tempo and Mode of Evolution Reconsidered." Paleobiology. 3:115-151.

Haldane, J. B. S. 1924. Transcripts of the Cambridge Philosophical Society. 23:19-41.
——. 1937. "The Effect of Variation on Fitness." American Naturalist. 71:735:337-349.

Lewin, R. 1981. "Evolutionary Theory Under Fire." Science. 210:4472:883-887.

Mayr, E. 1954. "Change of Genetic Environment and Evolution." In J. Huxley, A. C. Hardy, and E. B. Ford (eds.), Evolution as a Process. London: Allen and Unwin, pp. 157-180.
——. 1963. Animal Species and Evolution. Belknap Press. See chapter 17, especially pp. 527-535.
——. 1967. "Evolutionary Challenges to the Mathematical Interpretation of Evolution." In P. Moorehead and M. M. Kaplan (eds.), Mathematical Challenges to the Neo-Darwinian Interpretation of Evolution. Philadelphia: Wistar Institute Press, pp. 47-58.
——. 1970. Populations, Species, and Evolution. Belknap Press. See chapter 17, especially pp. 302-310.

Simpson, G. G. 1944. Tempo and Mode in Evolution. New York: Columbia University Press.
——. 1950. The Meaning of Evolution. Oxford University Press. See p. 97.
——. 1953. The Major Features of Evolution. New York: Columbia University Press.
——. 1976. "The Compleat Palaeontologist?" Annual Review of Earth Planetary Science. 4:1-13.

Williamson, P. G. 1981. "Paleontological Documentation of Speciation in Cenozoic Molluscs from Turkana Basin." Nature (London). 293:437-443.

Wright S. 1949. "Population Structure in Evolution." Proceedings of the American Philosophical Society. 93:471-478.

About the Author(s): 
Frank J. Sonleitner is an associate professor of zoology at the University of Oklahoma in Norman.
© 1987 by Frank J. Sonleitner
This version might differ slightly from the print publication.