The ID Report

By Robert Deyes
ARN Correspondent

Together with Stephen Jay Gould, paleontologist Niles Eldredge is known for having exposed the predominance of an evolutionary phenomenon called 'stasis' or 'non-change'. For Eldredge, his moment of realization came while studying the fossilized fauna of a period in the earth's history that paleontologists today call the 'Devonian' (Ref 1, Chapter 2). Today we know of the Devonian mainly because of a smattering of rock formations throughout the eastern United States. One particular Devonian animal, a trilobite by the name of Phacops rana, captured Eldredge's interest because of the apparent lack of morphological variability between species (Ref 1, Chapter 3). Eldredge noticed for example that, regardless of where he got his specimens from, they always had a similar arrangement of eyes. Not only were the individual lenses of their compound eyes arranged into columns but, regardless of the geographical locale from which he had obtained his trilobite specimens, the number of lens columns never appeared to deviate from 16-18. Eldredge's observations were telling. As he wrote,

"We climb up those rocks and check those samples, over what must be, in some total, a 3-or-4-million-year period, we see some oscillation, some variation, back and forth-but no real change at all, and no change especially in the anatomical feature, those columns of lenses in the eyes....This is the first element: simple lack of change. Stability, or stasis, as Gould and I began to call it" (Ref 1, p.70)

Many more cases of stasis have since been documented in the fossil record although in many of these, the reality of stasis has not been accepted with enthusiasm. In Eldredge's own assessment, evidence for stasis in the fossil record has become, "something of a professional embarrassment to be politely ignored, so alien did it seem to what evolution ought to look like in the fossil record" (Ref 1, p.120), Unwilling to simply sweep the evidence under the carpet, Eldredge and Gould decided to accept the fossil record for what it showed- long periods of morphological stasis interrupted only every few million years by sudden moments of morphological change (Ref 1, p.120). Science writer David Quammen has since also drawn attention to this rather striking phenomenon:

"Anyone who considers the biogeographical data...must be struck by the mysterious clustering pattern among what [Darwin] called "closely allied species"...Paleontology reveals a similar clustering pattern in the dimension of time...closely allied species tend to be found adjacent to one another in successive strata. One species endures for millions of years and then makes its last appearance in, say, the middle Eocene epoch; just above, a similar but not identical species replaces it" (Ref 2, p.12)

Writing in his opus The Structure of Evolutionary Theory, Gould presented a detailed treatise of his theory on punctuated equilibrium that, as he outlined in one of the key chapters of this work, describes the fossil record not as a continuum of graduated forms connecting related species but rather as a series of intermittent punctuated changes that occur between long periods of morphological 'stasis' (Ref 3, pp. 875-885). One of Darwin's contemporaries, the paleontologist Hugh Falconer, wrote a monograph to Darwin about the great mammoth and drew attention to, "the persistence in time of the distinctive characters of the European fossil elephants" (Ref 3, p.747). Falconer's realization was critical for not only did it reveal how specific observable characters were morphologically constant within given species of mammoths but also how such constancy existed in spite of great climatic variations. The mammoth's existence through the ice age was Falconer's primary example:

"If we cast a glance back on the long vista of physical changes which our planet has undergone since the Neozoic Epoch, we can nowhere detect signs of a revolution more sudden and pronounced...than the intercalation and subsequent disappearance of the Glacial period. Yet the dicyclotherian Mammoth lived before it, and passed through the ordeal of all her extremities with it involved, bearing his organs of locomotion and digestion all but unchanged" (Ref 3, p. 747).

Even in the face of major environmental change- the very fodder that was supposed to drive natural selection- morphological constancy appears to have prevailed. The predominance of stasis of form in the fossil record without any intermediate links that connect disparate forms to common ancestors is a reality that paleontologists are today having to come to grips with. Contravening a dogma founded on expectations rather than on what the fossil record revealed, it was both Gould and Eldredge who took on the scientific establishment by bringing to public attention not a continuum of graduated forms connecting related species but instead the presence of intermittent punctuated changes between long periods of morphological 'stasis' during which species remained unchanged for millions of years. At the very least, the predominance of stasis should be prompting us to execute a radical 'face lift' to the way we consider evolution.

References

1.Niles Eldredge (1985), Time Frames: The Rethinking of Darwinian, Evolution and the Theory of Puctuated Equilibria, Published by Simon and Schuster, New York

2.David Quammen (2004), Was Darwin Wrong?, National Geographic Magazine, November 2004, pp.4-31

3.Stephen Jay Gould (2002), Punctuated Equilibrium and the Validation of Macroevolutionary Theory, pp.745-1022 in, The Structure of Evolutionary Theory, Belknap Press of Harvard University Press, Cambridge, Massachusetts