Revolutions in the History of Science and the History of Life: The Influence of Kuhn on Gould and Eldredge’s theory of punctuated equilibria

I wrote this essay at the start of last summer at the end of my Lower Sixth year as part of an extension project for A-Level Philosophy inspired by finding Turner’s Paleontology: A Philosophical Introduction and being given The Structure of Scientific Revolutions at an impressionable age. I have now decided to dig it out and publish it unedited since then, retaining my youthful zeal, naivety and poor essay titling skills.

Thomas Kuhn was one of the most influential 20th century philosopher of science known primarily for his idea that science advances by a series of revolutions. During a paradigm shift, the fundamental theoretical foundation of a science is overturned and a new generally accepted theoretical foundation, or paradigm, is established. Kuhn’s analysis of the way that scientists work, detailed in his essay The Structure of Scientific Revolutions, has influenced the way that scientists in general have thought about the way in which they do science. But the intellectual framework of Kuhn’s theory has influenced scientist further, even in the extent of influencing heavily the formulation of a scientific theory.

Stephen Jay Gould and Niles Eldredge’s theory of punctuated equilibria states that it is best to take a literal reading of the fossil record, as it actually shows long periods of stasis where species stay the same, punctuated by the rapid appearance of new species. The theory is commonly described as “Marxist”, often as an insult, despite that Marx, and other Hegelians, believed that everything in history is leading to a single goal or end-point; a telos. Gould and Eldredge stressed the contingency of evolutionary history, and hence evolution does not occur towards a telos. Hence, the lack of an end goal that Gould and Eldredge posited for evolutionary history distinguishes his broad theory of evolutionary history from Marx’s theory of human history. However, we will see that the structure of the theory of punctuated equilibria is much more similar to the structure of Kuhn’s theory of scientific revolutions, and indeed, that punctuated equilibria could not have been formed as a theory without the intellectual framework Gould and Eldredge borrowed from Kuhn and other philosophers of science. Though many scientists do not consider detailed philosophical study to be important, I will argue that punctuated equilibria is a good example of where a scientific theory could not have been formulated without a study of philosophy and the adoption of the sort of thinking common amongst philosophers of science.

Kuhn suggested that the history of an established, mature science is characterised by long periods of normal science, under which almost all scientists work with the same paradigm. Paradigms are suitably opened ended so that scientists work to “patch up” the science by asking unanswered questions, but seldom question the theoretical foundation of the science. Occasionally, the paradigm strains under the increasing weight of anomalies that scientists find in the data, so the data cannot be seen to be compatible with the current paradigm. Then a scientific revolution may occur; where an often younger, outsider scientists proposes a new theory for the interpretation of the data that explains enough of the anomalies to challenge the current paradigm. If enough scientist pledge allegiance to this new theory, it will become a paradigm. This shift from one paradigm to another is not wholly rational; it is due to a wide range of personal, sociological, psychological and professional considerations as well as the strength of the evidence. The new paradigm becomes incorporated into normal science, and a period of stability occurs as scientists labour under the same, new paradigm. Scientists must use background theories to decide where and how to collect data and the ways in which they analyse data. But this data obtained are interpreted (or possibly actually seen) in line with the particular paradigm that the scientist is working under, so data is theory-laden. Furthermore, Kuhn argued that science is not advancing to a goal of an immutably truth, clearly set by nature. Rather science evolves through revolutions, but to no particular goal, in a similar way that living organisms evolve, without a goal or telos.

Therefore, the broad frame work of Kuhn’s theory is characterised by: long periods of stasis, where the paradigm remains the same, punctuated by rapid periods of revolution, where a new paradigm emerges, but does not move the scientific field towards the goal of absolute truth. Hence, we can trace the intellectual trail from Kuhn’s theory to Gould and Eldredge’s punctuated equilibria; which is similarly characterised by long periods of stasis, where species remain the same, punctuated by rapid periods of revolution, when new species appear, but does not move the evolution of life towards an absolute goal of evolutionary fitness.

In order to understand Gould and Eldredge’s theory, it is important to understand what it was formulated to counter. Darwin wrote that evolution occurred gradually, primarily by natural selection, involving the gradual evolution of one form or species into another, a process known as phyletic gradualism. Darwin himself said that this view of evolution did not reflect what is shown in the fossil record, as there is no evidence of enormous numbers of intermediate varieties, so the fossil record cannot be interpreted as revealing “any such finely graduated organic chain”1 of species splitting and evolving into different species. But Darwin conceded that “the geological record is extremely imperfect and this fact will to a large extent explain why we do not find interminable varieties, connecting together all the extinct and existing forms of life by the finest graduated steps.” So the phyletic gradualist would see the fossil record as showing gradual evolution littered with gaps, and in many of these gaps fall transitional forms.

However, in 1972, Stephen J Gould and Niles Eldredge presented their theory of punctuated equilibria2, though it is a different way of seeing the fossil record rather than a true theory. They posited that the fossil record in actuality shows an ancestral species in an older layer of rock and many descendent species in the next youngest layer of rock with no intermediary form between the ancestor and the descendants. Phyletic gradualists would see this as a “gap” in the deposition of sediment, due for example to a lake drying up, and therefore a thin layer of rock represents a long period of time in which speciation was occurring gradually. Hence, the phyletic gradualist reassures themselves again that speciation is gradual and the fossil record is incomplete. Gould and Eldredge bemoaned the confines of the phyletic gradualist picture: “We have all heard the traditional response so often that it has become extremely imprinted as a catechism that brooks no analysis: the fossil record is extremely imperfect. […] renders the picture of phyletic gradualism virtually unfalsifiable.”

Therefore, they said, what grounds do we have for not taking a literal reading of the fossil record? Maybe the apparent “jump” between ancestor and descendants is not an artifice due to geological particularities, but represents something actually occurring in evolution. The literal reading invites the proposition that, often, species do not differentiate gradually. Species could differentiate by a subpopulation breaking off from the main population, the small numbers of the isolated subpopulation on the periphery of the ancestor’s range experience a different environment, so the lineage splits into two new descendent species rapidly. The descendants then reinvaded the ancestor’s geographical range, a process known as allopatric speciation. When species become established, they do not change for long periods, until the lineage becomes punctuated by another speciation event. This happens in too short a time period and in a different geographical range to most of the rest of the population, therefore the fossils of the ancestor and the transitional forms are extremely unlikely to be found directly about each other in the same stratum until the new descendent species reinvades. So, most of the time, no “insensibly graded fossil series.”2 is captured in the fossil record. The ancestor, transitional forms, descendants series occurs at a faster tempo than Darwin suggests, and these events are interspersed with periods of stasis.

Though Darwin did not posit that evolution had a telos, he did formulate his theory using the standard frame-work of Victorian, ideas of gradual historical progress and Hegelian teleology. Indeed, it is very likely that Darwin could not have come up with punctuated equilibria however hard he tried, given the intellectual environment he worked in. Gould and Eldredge are indebted to Kuhn for their frame-work for punctuated equilibria. But furthermore, their presentation of their theory was done so in a way that acknowledges Kuhnian ideas of the theory-ladenness of science, remarkably modest behaviour.

Their formulation of punctuated equilibria is based on idea of the theory-ladennes of evidence used by Kuhn; that your background theories, or the paradigm you are working under, might lead you to interpret (or even actually see) the data in a way different from another scientist working under a different paradigm. Hence a phyletic gradualist and a punctuated equilibria adherent may each interpret the same fossil sequence differently from the other; the former would interpret there to be gaps in the formation of rock, giving the appearance of an interrupted gradual evolutionary process but the latter would interpret there to be no actual gaps in the rock formation, but rather the “gaps” show suggests a period of rapid evolution in a different geographical area. Gould and Eldredge write, in a remarkably Kuhnian style, in their original paper, that “the idea of punctuated equilibria is just as much a preconceived picture as that of phyletic gradualism. We readily admit our bias towards it and urge readers, in the ensuing discussion, to remember that our interpretations are as coloured by our preconceptions as are the claims of the champions of phyletic gradualism by theirs.”2 Hence, Gould and Eldredge stress punctuated equilibria as just another way of seeing, and they are as biased towards it as Kuhnians as Darwin was to gradualism as a Victorian.

In their original paper, Gould and Eldredge went so far as to say that “the data of palaeontology cannot decide which picture [phyletic gradualism or punctuated equilibria] is more adequate”. Though later claiming that punctuated equilibria could be verified, here the theory-ladennes of evidence is suggested to an extreme degree, as they suggest that our interpretations are not merely “coloured by our preconceptions” but wholly fogged, implying disturbingly that we cannot know anything inductively, as everything is hidden implicitly in our theories, or paradigms.

This extreme approach did, however, not bring many adherents to punctuated equilibria, hence their later concession that punctuated equilibria could survive tests against the data. With this verificationist approach, Gould and Eldredge have won over the vast majority of younger scientists to varying extents, and hence launched the palaeobiological revolution.

In conclusion, the work of Kuhn and other philosophers in the philosophy of science heavily influenced the formulation and presentation of the scientific theory of punctuated equilibria, itself a considerable contribution to modern evolutionary thought. Therefore, I stress the importance of scientists learning about philosophical ideas, if only for the sake of scientific innovation. Broadening the intellectual horizons can only bring the possibility of scientists applying theoretical frame-works in novel ways to allow radical reinterpretations of current theories. If scientists learn to think like philosophers, at least some of the time, it can bring about innovative interpretations of nature, which is vital for the continued relevance, usefulness and intellectual robustness of science.

Bibliography:

  1. Darwin, C. On the Origin of the Species (1859)
  2. Gould, S. J. , Eldredge, N. Punctuated Equilibria: An Alternative to Phyletic Gradualism (1972)
  3. Turner, D., Paleontology: A Philosophical Introduction (2011)
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