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.


  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)

Phallocentric Fallacies: On Gender Bias in Science

In the media and in the science classroom, it is common to hear the lamenting of the lack of women in science at the highest level. This is made evident in the statistics, such as the 12.8% of the STEM workforce in the UK being women as of 2014. The world over and in the majority of scientific disciplines, women are conspicuously absence at the highest level. Most agree that this is not due to women’s inherent inability to do science or their lack of ambition to do anything but raise their children. Therefore the gender disparity at the leading edge of scientific research and innovation is often bemoaned as a shameless waste of talent. In such an example, Athene Donald explores the phenomenon of girls interested in physical sciences being subtly or unsubtly discouraged from taking A-Level Physics and being “lost” from the path to a career in physics or engineering. Donald argues that such a phenomenon is harmful to the economy, as to simply maintain the status quo in terms of science industries in the UK, we need 10,000 more STEM graduates than we had graduating as of 2012, according to the Royal Academy of Engineers.

I don’t deny that women aren’t needed to make up the numbers of competent STEM professionals if we hope to expand STEM industries. Furthermore, I agree with Donald that it reflect poorly on an intellectual culture if those who are academically able and motivated to pursue a field of interest are discouraged from doing so for reasons unrelated to their ability.

However, these arguments apply to encouraging anyone who has the merely inkling of interest in science to pursue it in the educational systems, so are not in principle incompatible with having the upper echelons of scientific institutions filled with men of a particularly narrow social slice if this is how the dice have fallen in terms of interest.

But I will argue that women, as well as everyone else who isn’t of the demographic which has been historically the definition of a scientist; the middle-class white European man, have more to offer science than just another pair of hands.Though science aims to be objective it is inescapably subjective as it is done by human beings with subjective experiences. We gain our subjective biases through how we experience our lives in our society, these background biases act as “blinkers” and inevitably limit our outlook on the ever elusive truth of reality. This narrowing is not out of stubbornness to see reason, as the perjorative use of “blinkers” entails, but means it is very difficult to see otherwise. As Elizabeth Anderson writes in Feminist Epistemology: An Interpretation and a Defence: There is no reason to think our presently cramped and stunted imaginations set the actual limits of the world, but they do set the limits of what we now take to be possible.”

Those who have very similar experiences due to their similar social backgrounds are likely to have similar “blinkers” and similarly narrow outlooks, which becomes the status quo. As Anderson writes: “A scientific community composed of inquirers who share the same background assumptions is unlikely to be aware of the roles these assumptions play in licensing inferences from observations to hypotheses, and even less likely to examine these assumptions critically.” In contrast, those who have different experience and interests through being socialised differently will have their own slightly different set of blinkers and fields of vision of reality slightly askew from the status quo.

Science done by those with very similar life experiences, such as coming from the same social class, same country, same educational background, same sex-class and so on can be very fruitful, I do not deny the achievements of the Enlightenment, but this can only go so far. The introduction of someone with different backgrounds, such as that of being a woman in a patriarchal society, into a field previously dominated by androcentricism, the centring of the male means that she brings with her a different set of subjective biases about the field, so her blinkers are slightly offset to those of her male colleagues and she may have an outlook subtly different, and may encompass a patch of reality the men have so far missed. By contrasting ideas developed by those with divergent outlooks, scientists in the field should then conduct experiments to work out which idea matches reality most closely, and therefore help edge science ever closer to the truth.With such similar subjective biases, a field can only go so far until old hypotheses become rehashed again and again until the empirical evidence relevant to them is exhausted. But using her subtly different outlook onto the world, the female scientist may be able to come up with an innovative hypothesis which after sufficient empirical corroboration may be a theory which comes closer to reality than male scientists with their own particular outlooks have until then been able to.

My focus here will be on the use of what Anderson describes as gender symbolism, “which occurs when we represent nonhuman or inanimate phenomena as masculine” or feminine” and model them after gender ideals or stereotypes.” I will use a historical example of this where gender ideals are mapped onto a biological phenomenon where in fact no sound evidence of it’s existence is found, a true phallocentric fallacy where the masculine is seen where it does not exist. The episode which sparked this articles comes from a particularly obscure branch (or hypha) of biology: fungal reproduction.

As Nicolas P. Money writes in Mushroom, 19th century mycologists were very interested in the topic of fungal sexual reproduction, though the difficulties of studying the phenomena meant that, whist most specialists seemed to favour “the gentle fusion of colonies”, no experimental data nor a mechanism for this was proposed. However, during the First World War, Worthington G. Smith (1835-1917) proposed that he had observed through his microscope mushrooms producing sperm cells, which were ‘ejaculated’ onto the spores in the soil. Smith’s observations are flawed on two fronts. Firstly, he seems to have struggled to see these sperm cells, writing that “At first it requires long and patient  observation to make out the form of these bodies satisfactorily, but when the peculiar shape is once comprehended, there is little difficulty in correctly seeing their characteristic form.” It sounds rather like to see these cells, you must know what to look for, so you see what you know. But his most egregious mistake was to hydrate his samples with the shocking non-sterile “expressed juice of horse dung”, no doubt containing sperm-like amoeba. However, it is highly likely that due to his experience as a man in the patriarchal Victorian society Smith could only imagine sexual reproduction to occur by the forceful ejaculation of the active male sex cells onto the passive female sex cells, a clear projection of the gender symbolism of Victorian society onto the natural world. His blickers contributed to the poor quality of his science, as he did not or refused to acknowledge the contaminating effect of the horse dung on his samples so certain his results were correct.

In contrast, the young graduate Elsie Maud Wakefield (1886- 1972) appears to me to be the model of the “New Woman”, a graduate of the then all-women’s Somerville College, Oxford. Though information on her biography is sparse, as a woman in the late 19th century and early 20th century she would likely have been aware of ideas about human sexual relations being more mutualistic and equal than the Victorian ideals of male dominant courtship, such as those later expressed in the work of Marie Stopes. Whether she adhered to these political values or not, she would have been better able to imagine a non-phallocentric natural world which Smith could not. Therefore, her subjective ‘blinkers’ were different enough from those of Smith’s that she was able to conduct her experiments on fungal reproduction without the phallocentric assumptions of the active male sperm and passive female spores.

Wakefield conducted a series of experiments which demonstrated the necessity of the fusion of the mycelium, the fungal ‘roots’, to produce mushrooms in the Basidiomycete fungi, with no role for mobile sperm cells. But as Wakefield discovered, the nuclei of the two colonies don’t immediately fuse when the colonies fuse, instead the fused colony grows and forms mushrooms with the two, unfused nuclei inhabiting every cell. Nuclear fusion, the event which occurs in animals when sperm meets the egg, only occurs in the mushroom just before spores are produced. Neither colony engaged in sex takes on an ‘active masculine’ or ‘passive feminine’ role which the Victorian Smith expected to find in society and in nature, and so the phallocentric system of gender symbolism breaks down.

I do not claim that women are able to tap a magical reserve of female knowledge gained purely by virtue of having a female body. This sort of crude gender essentialism only aids in cementing differences. Instead, I argue that simply because no two people can ever occupy the same position in time and space, each person’s subjective experience of reality will be slightly different from that of others, and so will have different background assumptions and interests when entering science, including biases based on being socialised as a woman or a man. Instead a shuffling of subjective, gender biased perspectives is where real scientific innovation and the hope of objectivity can be found. As Anderson writes, “Each individual might be subject to perhaps ineradicable cognitive biases or partiality due to gender or other influences. But if the social relations of inquirers are well arranged, then each person’s biases can check and correct the others’.In this way, theoretical rationality and objectivity can be expressed by the whole community of inquirers even when no individual’s thought processes are perfectly impartial, objective, or sound.”