Ten years ago, the great palaeontologist and evolutionary biologist Stephen Jay Gould died in New York of cancer. It was the second time that Gould had faced this terrible disease and this time he was defeated by it. The name of Gould will always be linked to his ‘punctuated equilibrium’ theory, published in 1977 with his colleague Niles Eldredge.
Stephen Jay Gould
“Many Breaks in the fossil record are real.” - Gould
The publication of this theory completely changed evolutionary biology: the general setting of the ‘Modern Synthesis’, the name given to the traditional paradigm of evolutionary biology since the 1930s, was totally shattered. The theory of ‘punctuated equilibria’ did not break with the basic core of Darwinian evolution – variation and natural selection – but it completely overturned the framework through which we understand natural history, from evolution's rhythm to the role played by natural selection.
Dialectical materialism sets out from the idea that that matter, the ultimate basis of our understanding, is always in motion, in a state of change. However, changes do not take place gradually but as a result of slow accumulation in quantity that, at a certain point, produces a qualitative leap.
We can see this process clearly at work in the physical and biological world but also in human societies. Revolutions are rare events that seem to come from nowhere, but in reality they are sudden leaps prepared by a long accumulation of apparently minor events. The way nature and society develop means that in order to effectively analyse natural and human history we cannot rely on a method of static study of separated facts. On the contrary, we must base ourselves on the dialectic method that understands any single event in a dynamic process of transformation.
Gould did not consider himself a Marxist, although he knew and used Marxism and his enemies always accused him of being one. This is because his theory broke with the traditional view of a slow, gradual evolution, something that fits very well with the mainstream ideology that defends capitalism as a system where standards of living are constantly improving.
Links between mainstream theories and the ruling class's ideology are inevitable, as scientists cannot isolate themselves from the class struggle going on in society. The struggle of ideas always reflects, even if not directly, a clash of opposite social interests and outlooks. Therefore it is not by chance that to reach a deeper understanding of how nature evolves, Gould and Eldredge were forced to break with the traditional paradigm that was also an implicit political statement about society. The theory of “punctuated equilibria” borrowed ideas from dialectical materialism but, above all, it enriched it enormously, revealing its importance to understand not only the life of Homo sapiens but of every life form on Earth.
At the origin of On the Origin
"There is a grandeur in this view of life." – Charles Darwin
When Charles Darwin in 1859 published his masterpiece, On the Origin of the Species by Means of Natural Selection, many attempts to introduce an evolutionist view of life had already been made by Denis Diderot, Pierre Louis Maupertuis, Comte de Buffon and others, but they were all based on speculation. None of these natural scientists had gathered sufficient observations and experimental evidence to back up the idea of evolution. Only the great zoologist Jean-Baptiste de Lamarck had developed a proper model of natural evolution, based on organic use and disuse and on a metaphysical “vitalist” force that pushed life forms forward.
The fact remains that the idea of a world in which species were created by God at the beginning of time was dominant. Scala naturae, the idea that God had placed all animals and plants on a fixed scale from the lower to the higher forms, was the accepted explanation of the diversity of life.
After his return in 1836 from the Beagle's 5-year voyage around the world, Darwin had become famous for the animal and plant collections sent to London, but more importantly he had collected the main data he would use to develop the theory of natural selection. Even a superficial reading of his famous notebooks proves that Darwin did not arrive at the idea of natural selection in a single step, but through successive approximations.
In 1838 Darwin read the famous An Essay of the Principle of Population, in which Malthus explained that, “Population, when unchecked, increases in a geometrical ratio. Subsistence only increases in an arithmetical ratio”, an iron law that forced animals and men to fight for their lives. This idea fitted well with the ideology that considered the aspiration of workers and peasants for a better life as unnatural. What was the point in raising the standard of living of these people if they were inevitably going to be decimated by famine? According to this school of thought it is nature that dooms most people to death or starvation, not society. Any attempt to change this simple fact was considered useless.
Although Malthus’ idea was very useful to the British ruling class it also helped Darwin to formulate the theory of natural selection. In fact, Darwin developed a close analogy between the large number of offspring produced in every generation and small number of adults who reached the reproductive age. The theory was completed with an analogy between the power of nature to select individuals and human selective power in the process of domestication.
On the Origin of the Species by Means of Natural Selection is the most important work in the history of biology. As Theodosius Dobzhansky wrote: “Nothing in biology makes sense except in the light of evolution”. The core of the Darwinian theory was very simple: there is a natural variation in terms of morphological, physiological or behavioural traits among the individuals of a population; these traits are heritable; individuals with traits that promote reproduction are preserved over the generations. The result is the progressive evolution of the entire population. In Darwin's words:
“Owing to this struggle for life, any variation, however slight and from whatever cause proceeding, if it be in any degree profitable to an individual of any species, in its infinitely complex relationship to other organic beings and to external nature, will tend to the preservation of that individual, and will generally be inherited by its offspring.” 
These conclusions did not arise from speculation but from careful observations and evidence from fossils, botany, zoology and other fields. The basic ideas of Darwin have been confirmed by thousands and thousands of different observations. That life forms evolve is by far the most established and important feature of nature.
The core of Darwinian theory was very simple but the consequences of the theory were revolutionary. If Nicolaus Copernicus and Galileo Galilei had removed humankind from the centre of the physical world, Darwin's theory shattered the ideas of humankind as the summit of the biological world. Moreover, his theory disposed of any ‘finalist’ and teleological view of nature. There is no ‘intelligent design’, nor a divine project behind evolution. It simply happens. It is the environment that silently shapes individuals on the basis of their random variations. Adaptations appear as consequences of life, that is in the struggle of plants and animals to survive. As Darwin wrote:
“I'm fully convinced that species are not immutable; but that those belonging to what are called the same genera are lineal descendants of some others and generally extinct species, in the same manner as the acknowledged varieties of any one species are the descendant of that species.” (Ibid., Introduction )
Thus the same theory explains two seemingly contradictory processes: on the one hand, the preservation of the most advantageous traits generation after generation; on the other hand an explosion of diversity from one common ancestor as a consequence of natural selection and the “survival of the fittest” (i.e. individuals with the most useful traits for reproduction). From the imbalance between the large number of offspring and the limited resources emerges the struggle for existence. That is the source of natural selection. In this view speciation and extinction have a dialectical relationship: species with less advantageous traits are progressively destined to disappear, opening up space in the environment in a constant process of change. This space will be filled by the new species emerging from the extinction of the former. In Darwin's view extinction is the condition of existence of new emerging species. According to Darwin, this is a slow and gradual process: an entire species gradually becomes a new species. Gould was eventually to define this gradual and slow view of evolution as “phyletic gradualism”.
For all its greatness, there were two main weaknesses in On the Origin. First of all, Darwin maintained an ambiguous explanation of how species arise. In fact, Darwin explained that a population of individuals selected by natural selection become a new species by slow, constant, imperceptible changes. Darwin admitted that geographic separation of small groups from the population could play a role in creating new species, but only marginally.
This gradualist view of evolution was influenced by the general ideology of gradualism in all spheres of life: natura non facit saltus [Nature does not make leaps] is at the core of any political, social, cultural and scientific thinking in all epochs that attempts to deny the possibility of changing society. In the theory of natural evolution, gradualism required the existence of uninterrupted intermediate stages in the fossil records, something that was never to materialise. Darwin himself attributed the lack of intermediate fossils to the difficulties in the process of fossilization, but the actual real fossil records that we do have show species that are unchanged for millions of years. Furthermore, what are the differences between variations and how did new species arise from these? New species seemed to vanish in a sea of variation: a well-marked variation is an incipient species.
In summary, we can see that the Darwinian paradigm of evolution had revolutionary features, but was also hampered by the ideological imposition of a gradualist view of natural history.
Darwin modified his book in the following edition to answer these critics. For example, we can read these words to explain the development of the eye shaped by a gradual, slow evolution by natural selection:
“Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real.” (Ibid., Chapter VI, Difficulties on theory )
“I may remark that, as some of the lowest organisms in which nerves cannot be detected, are capable of perceiving light, it does not seem impossible that certain sensitive elements in their sarcode should become aggregated and developed into nerves, endowed with this special sensibility.” (Ibid., Chapter VI)
The second problem was that Darwin, in setting up his theory, did not know exactly how the characteristics were transmitted to the next generation. This was pivotal for a theory based on natural selection, because one of the main elements of the theory was the presence of variations among the individuals and the possibility of transmitting the variations to the next generation. Without these two points it is not possible to have evolution.
In On the Origin, Darwin left open the question and, a few years later, he published an essay entitled ‘The variation of animals and plants under domestication’, in which he talked about a “provisional theory of the pangenesis”. According to this theory, characteristics come from every single point of the body and are accumulated in the gonads: the offspring are merely the product of mixing both parents' characteristics and not, as we know today, the product of random genetic reworking before the fusion of germ cells. It is clear that according to the “provisional theory of pangenesis”, the random emergence of advantageous variations cannot be inherited in full by the offspring but are diluted by mixing. Natural selection would have nothing to preserve.
Our understanding of the inheritance mechanism depends largely on Gregor Mendel's work. Today we know that there are precise mechanisms through which characteristics are inherited. Mendel's work, published in 1865, went basically unnoticed. Darwin received Mendel's work but he never opened it. However, from the publications of Mendel's work, especially with the discovery of the structure of DNA in 1959, the problems raised by On the Origin have now been basically solved. Today there are still many questions in the programme of evolutionary research that remain open, but they all start from the Darwinian core of evolution led by natural selection. There has been much research into the most appropriate scientific methods with which to define a species, a phylogenetic relationship, to understand the fossil records, to interpret the tempo and mode of the Earth's natural history and, above all, of humankind's natural history. It is a great leap forward for us and today this allows us to say that evolution is a fact.
Without the giant leap forward represented by the theory of evolution, it would not be possible to understand the relationships between all of the planet's phyla and our own history. Unless, of course, one believes that a superior being created all the animals exactly as they are today, and that the same supreme being buried a lot of dinosaur fossils simply to play games with humanity!
Ever since the publication of On the Origin, biology and science in general has never been the same. The theory of evolution by natural selection contains a profound dialectical meaning: conservation through diversity is a wonderful demonstration of the dialectical character by which nature proceeds. Karl Marx and Friedrich Engels immediately acknowledged the revolutionary implications of the theory pointing out, at the same time, the limits represented by the implicit ideology that lay behind it.
Every ruling class has an ideology to back up its domination. Before capitalism, the productive forces were growing so slowly that the very idea of change seemed irrelevant. The ideological justification of class power then was based on the idea of a motionless life, a universe always identical to itself that God had created that way and had given to humankind (that is to the ruling class) to rule over. Everything was identical since the Creation. Evolution was meaningless, in nature as in society. On the contrary, tradition, ipse dixit, and old habits held sway.
Evolution as an ideology
"Darwin is absolutely splendid" – Friedrich Engels
The emerging capitalist class in its struggle against the old ruling classes used the ideological weapons of individualism, personal ambition and merit: they deserved to rule because they were better, smarter than the others. According to the bourgeois outlook, by pursuing his own interests an individual becomes better and improves society as a whole: competition is good for everyone.
During the Middle Ages, competition among nobles, although often based on economic reasons, was always ideologically supported on moral grounds (the code of chivalry and so on). Now, with the new emerging bourgeois society, competition was simply the means by which human beings could do better, that is to get rich and powerful. The old pessimistic philosophy of homo homini lupus [man is a wolf to his fellow man] took on a new meaning: i.e. every businessman has the moral right to crush his competitors. In doing this, he helps humankind to improve. The idea of the “struggle for life”, as we noted, was not borrowed by bourgeois ideologists from the naturalists but it was the other way round.. It was the ideological outlook of the bourgeois that was imposed on the naturalists. In this context, evolution was acceptable, indeed it was a mirror of society as Steven Jay Gould notes:
“The theory of natural selection is a creative implementation of the principles of economics from Adam Smith to that of biology: the natural balance and order are not determined either by a superior control and external (divine) or by laws operating directly on the entire system: it springs from the struggle between individuals for their own benefit.” 
Thus, competition produced a progressive gradual improvement of society. What a marvellous propaganda tool for the rising capitalist class! The law of survival of the fittest was as valid in the jungle as it was in society.
A critique of the ideologies and theories of the ruling classes has been a fundamental task of Marxism since its very early days, which has been absolutely essential to help give clarity to the nascent labour movement. The founders of scientific socialism dedicated all their lives to studying the main discoveries of the natural and social sciences, assessing the scientific and political meaning of new ideas. The new ideas of Darwin featured among these.
In fact, it is remarkable to see how quickly Marx and Engels grasped both the importance of Darwin and his limits. This is because, in reality, they realised evolution was a reality even before Darwin. For instance, Marx wrote in 1844:
“Generatio aequivoca [spontaneous generation ]is the only practical refutation of the theory of creation. Now it is certainly easy to say to the single individual what Aristotle had already said: You have been begotten by your father and your mother; therefore in you the mating of two human beings – a species-act of human beings – has produced the human being. You see, therefore, that even physically man owes his existence to man. Therefore you must not only keep sight of the one aspect – the infinite progression which leads you further to inquire: Who begot my father? Who his grandfather? Etc.” 
Needless to say, at the time Marx was no more than a radical philosopher, with a rough understanding of the debate on evolution. But what it reveals is that the founders of scientific socialism were always interested in this topic. When in 1859 some hundreds of copies of On the Origin of Species came out, one of them was bought by Engels. And within just a few days he understood that science has changed forever. What is even more remarkable, however, is that Engels was also able to immediately detect the weaknesses of Darwinism. He wrote:
“Darwin, by the way, whom I'm reading just now, is absolutely splendid. There was one aspect of teleology that had yet to be demolished, and that has now been done. Never before has so grandiose an attempt been made to demonstrate historical evolution in Nature, and certainly never to such good effect. One does, of course, have to put up with the crude English method.” 
Marx and Engels also recognized that in many aspects, Darwin used an approach that was similar to historical materialism in many ways. Marx stated in the preface to the second edition of Capital that from his standpoint: “...the evolution of the economic formation of society is viewed as a process of natural history”. Engels, in summing up at Marx's funeral the achievements of his lifelong friend and comrade stated: “Just as Darwin discovered the law of development of organic nature, so Marx discovered the law of development of human history” . Darwin on his part was frightened by the interest Marx took in his ideas as we can see from how he replied to Marx thanking him for sending him a copy of Capital .
In the following years, Marx and Engels always defended Darwin against his critics. But they were also aware of the fact that the weak points in Darwinism were used to support capitalism, becoming part of the dominant ideology. Marx, for instance, wrote to Engels:
“It is remarkable how Darwin rediscovers, among the beasts and plants, the society of England with its division of labour, competition, opening up of new markets, ‘inventions’ and Malthusian ‘struggle for existence’. It is Hobbes' bellum omnium contra omnes and is reminiscent of Hegel’s Phenomenology, in which civil society figures as an ‘intellectual animal kingdom’, whereas, in Darwin, the animal kingdom figures as civil society.” 
The fact that Darwin was not a radical, to say the least, was detrimental to his theories. Capitalist ideology was a fetter on the development of the theory of evolution. This was particularly clear with gradualism. For Marx and Engels it was obvious that gradualism has nothing to do with evolution. In a letter to Engels, Marx quotes a minor scientist of his time precisely because he rejected gradualism:
“A very important work which I shall send on to you (…) is: ‘P. Trémaux, Origine et Transformations de l’Homme et des autres Êtres, Paris 1865. In spite of all the shortcomings that I have noted, it represents a very significant advance over Darwin (…) Progress, which Darwin regards as purely accidental, is essential here on the basis of the stages of the earth’s development, dégénérescence, which Darwin cannot explain, is straightforward here; ditto the rapid extinction of merely transitional forms, compared with the slow development of the type of the espece, so that the gaps in palaeontology, which Darwin finds disturbing, are necessary here.” 
The ‘specialists’, that is professional biologists and evolutionists, were to take another century before they could grasp this idea, as we will see in discussing Gould. This was not by chance. The role of gradualism was not minor. Evolution could be accepted only inasmuch as it was forced into a gradualist theory. Darwin was instinctively aware of this.
Darwin’s theory produced a complete break with previous ideas about natural life. We will touch on two points that are particularly important for the shaping of bourgeois ideology. The first is the end of teleology in science. As Marx put it: “It is here that, for the first time, ‘teleology’ in natural science is not only dealt a mortal blow but its rational meaning is empirically explained.” 
The role of gradualismIncredibly complex structures and behaviours are not the results of conscious efforts. God is no longer needed to understand the miracle of life. On the one side, this implies that human beings are not a special breed created by God but animals among animals as Thomas Huxley, for instance, noted in Man's Place in Nature, the fact that the human embryo is very similar to that of apes, etc. This means that religion had for ever lost its power to “explain” the world as we know it. That is why priests of any creed hate Darwin.
On the other side, however, Darwinism is used to prop up capitalism: an invisible hand works in nature as in society. And therefore any human intervention is useless. However, this transposition is baseless. All animals struggle to survive with the tools evolution has given to them. It just so happens that for humankind to survive our ancestors developed language, consciousness, cooperation, in a word, planning. The first humans started to differentiate from other bipedal apes exactly because they were able to plan: they planned hunting, they planned how to build their habitations, they planned ahead. They had to, in order to survive. To act with an end in sight is exactly what is specifically human. As Marx noted:
“We pre-suppose labour in a form that stamps it as exclusively human. A spider conducts operations that resemble those of a weaver, and a bee puts to shame many an architect in the construction of her cells. But what distinguishes the worst architect from the best of bees is this, that the architect raises his structure in imagination before he erects it in reality. At the end of every labour-process, we get a result that already existed in the imagination of the labourer at its commencement.” 
Therefore, the immense progress produced by Darwin when he refuted a visible hand as the cause of changes in the natural world does not mean that humankind is doomed to an anarchic society, that is to capitalism. We are aware of the laws of production. This is quite a difference from other animals.
The second point is that things change. Animals change, species are born and disappear. This aspect too was imported into social analysis, because it was useful to consolidate the idea of capitalism as a progressive system. The problem, however, is that if society evolves and nothing lasts forever, then capitalism too is doomed. Bourgeois ideology has therefore a contradictory relation with evolution. That is why they proposed an idea of history where evolution and even revolution was good until capitalism came into being, but no longer once it had been established. As Marx put it: “[the laws of capitalism] are eternal laws which must always govern society. Thus, there has been history, but there is no longer any” 
Capitalism is the end of history, of human evolution. The problem is that evolution never ends. Therefore, in allowing evolution into human life even under capitalism, they did so but as a gradual imperceptible modification of minor points of reality, because the fundamental pillars of society, that is the bourgeois ownership of the means of production with everything that flows from it, should be held as eternal. Gradualism is not a minor aspect of evolution that some scientists accept and others don't. It is the only way of reconciling evolution and capitalism. That is why the role of Steven Jay Gould's theory is paramount, as we will see.
Bourgeois ideologists are not the only ones to have misinterpreted Darwinism. On the idea of the “struggle for life”, the ultra-left philosopher Antonie Pannekoek wrote that, “Darwinism is the scientific proof of inequality” and hence for him it was intrinsically anti-socialist . In his lack of understanding, he stated the following: “Socialism wants to abolish competition and the struggle for existence. But Darwinism teaches us that this struggle is unavoidable and is a natural law for the entire organic world. Not only is this struggle natural, but it is also useful and beneficial”. What, in effect, he was combatting was Thomas Malthus, or Social Darwinism, not the Darwinian theory of evolution.
Ideological justifications for class inequality were nothing new; they can be traced back to the famous Apologue of Menenio Agrippa or even to Mesopotamian texts written sixty centuries ago. There is not a word by Pannekoek – on the contrary – about the little problem that struggle also means class struggle and that evolution could entail the overcoming of present-day natural as well as social structures. That is why – in spite of the attempts to use the theory of evolution to the advantage – Darwin, Huxley etc., were hated by the reactionary cliques of their time.
As for gradualism, the most famous theoretician of the Socialist International, Karl Kautsky, accepted gradualism because it fitted with his own reformist outlook of social evolution. This was not by chance. Just as capitalist ideology can accept evolution only within the straitjacket of gradualism, the same is true for reformism, that is the ideological reflection of bourgeois power inside the workers' movement. Thus, slowly, gradually, without a revolutionary break, capitalism becomes socialism, just as a species transforms into another. In reality this does not happen either with species or with societies. Once again, we see how a scientific refutation of gradualism is fundamental and Gould achieved this brilliantly.
The rise of the paradigm
The Darwinian research programme that dominated natural science in the twentieth century is defined as the “Modern Synthesis”, a name that suggested the fusion of the central core of the Darwinian theory – casual variation and natural selection – with the knowledge of genetic population that arose in the 1930s.
For the first time evolution was enriched with a full comprehension of the mechanisms by which variation and inheritance emerge. In the time that separates the publication of On the Origin from the rise of the ‘Modern Synthesis’, biology eventually understood that traits of both parents are transmitted according to precise mathematics laws, elaborated by Gregor Mendel, the father of modern genetics. The consequences of this were huge: traits developed by the parents during their lives were not transmitted and the evolution of animals and plants was not the consequence of a simple adaptation to the needs posed by the environment, based on the use or disuse of organs. On the contrary, it confirmed that the mechanism worked the other way round: the environment selects randomly produced modifications.
On this basis Darwinian theory became a paradigm of a sort of omnipotence of natural selection: traits, adaptations, behaviours are directly shaped by natural selection. This paradigm was embodied by the ‘Modern Synthesis’: Ronald Fisher, Sewall Wright, Theodosius Dobzhansky, Ernst Mayr and George Gaylord Simpson were the main protagonists of this fruitful research programme that, over a period of 40 years, transformed the theory of evolution from being a viable hypothesis to an incontestable scientific fact. Each of these scientists gave a strong contribution in different fields of evolution.
In his famous work The Genetical Theory of Natural Selection, Fisher proved that the genetic basis of evolution could be extended to those traits, such as height, that do not appear to be transmitted in a Mendelian manner. In fact, until then scientists thought that traits like height could not depend on specific genes like the hair colour. Fisher showed that it was not the case: genes encoding for height work like the others, following the same laws. We can predict the transmission frequencies of the genes. This was the first success of the ‘Modern Synthesis’.
Wright developed Fisher's theory with the discovery of genetic drift. This mechanism is enriched by natural selection and shows the potential for random emergence (or disappearing) of a given characteristic with the passing of generations. In Wright's view, a population can be divided into sub-populations that gradually, through genetic drift, can colonize new areas and spread due to their ‘positive’ traits. In other words, Wright's theory was a predictive mathematical model of the slow and gradual change embodied in the ‘Modern Synthesis’.
The great geneticist Theodosius Dobzhansky made an important step forward in our understanding of what a species is. In his most famous work Genetics of the Origin of Species, written in 1937, for the first time evolutionary biology gained a unifying definition of a species. This view was called the “biological definition of species” and it was based on the mechanisms of reproduction: a species is a group of individuals each fertile and reproductively isolated from others. In the words of Dobzhansky:
“Species are the smallest discrete groups of organisms whose free interbreeding with other groups is prevented by some physiological isolating mechanisms.” 
Individuals of different species are separated by specific isolating mechanisms like incompatibility of genitalia, gametes, periods of fertility, sterility of the offspring etc. Yet in the words of Dobzhansky:
“(...) the production of hybrid offspring between two discrete groups may be prevented by a lack of sexual attraction between different individuals, by a physical non compatibility of the reproductive organs (genitalia or flower structure), by differences in the structure or physiology of the sex-cells, differences in the breeding seasons, and the ecologies of the parents. If produced at all, the hybrid may be too weak to attain sexual maturity, or be sterile because of the non-production of functional gametes.” (Ibid.)
This theory greatly strengthened the core of the Modern Synthesis: i.e. that evolution is a slow and gradual process just as Darwin showed many years ago. Genes and genetics provide the mathematical basis of this theory and species are formed in the same way:
“It is only through the development of isolating mechanisms that different organisms may coexist in the same area, may produce new forms on which progressive evolution can be based, or differentiate and specialize to exploit the different 'niches' in the economy of nature” (Ibid.).
From these lines we can understand that the core of the “Modern Synthesis” was the extrapolation of the mechanism of microevolution to that of macroevolution: in other words, the gradual changing of the gene frequencies over the generations, that is the basis of the formation of a new species, is also the basis of the formation of the superior taxa, like fishes, amphibia, reptiles, birds and mammals. There is only one mechanism at work for the Modern Synthesis and the process evolves in a gradual manner. Everything we do not find in the fossils records is merely due to the difficulties in the process of fossilization.
George Gaylord Simpson's Tempo and Mode in Evolution, published in 1944, was the main work that explained this gradual interpretation of evolution. In this work, Simpson summarized the extrapolation of microevolution in the macroevolution and underlined that most evolution proceeds through steady and gradual phyletic transformation of the whole lineage. This interpretation is named “anagenesis” or “phyletic gradualism”.
The Modern Synthesis was a great step forward for Darwinian theory. Its biological definition of species is still valid today even if scientists are suggesting and analyzing new ways of formation of species. The first cracks in the Synthesis, however, would not directly come from the genetic and biological mechanisms of formation of species but from the paleontological data and from the mechanism of geographical distribution of species.
Every scientific theory goes through a period of consolidation, where new discoveries strengthen and extend it. At a certain point these new discoveries lead to a new and more accurate interpretation of the same data. Starting with the development of the same theory in a new form, at a certain point, it becomes a new theory. This is how scientific development evolves, through dialectics: a quantitative approximation of reality that, at a certain point produces a qualitative leap forward that incorporates the main discoveries of the previous theories, but also denies important aspects of those same theories.
First cracks in the paradigm
After being generally accepted as correct, a theory passes through a period of questioning. This was also the case with the Modern Synthesis and the theories of punctuated equilibrium. From the 1930s to the 1950s, the dominant paradigm was strengthened by the discoveries of genetics: the paradigm of evolution based on gradually changing gene frequencies was reinforced by the works and the analysis of Ronald Fisher and Theodosius Dobzhansky.
However, with the triumphs also came problems and a new interpretation began to emerge. In the aforementioned work of George Gaylord Simpson, Tempo and Mode in Evolution, although it was an orthodox brilliant work of palaeontology of the Synthesis, it also proposes the idea that the tempo and mode in which evolution proceeds are not the same thing. Above all, Simpson admitted that fossil records show us different rhythms of evolution. This idea, however, was ignored for many years by mainstream scientists.
Eventually, the first real crack in the paradigm was represented by Animal Species of Evolution, published by the ornithologist Ernst Mayr in 1963. Mayr was one of the most important evolutionary biologists of all time. He was a zoologist, a tropical ornithologist and, above all, the discoverer of the “allopatric theory of speciation” based on the data he had collected for many years as an ornithologist. This was a revolution in the way we consider how a species is formed. And Mayr was aware of the limitations of the Modern Synthesis:
“As a consequence, geneticists described evolution simply as a change in gene frequencies in populations, totally ignoring the fact that evolution consists of the two simultaneous but quite separate phenomena of adaptation and diversification.” 
In Mayr's view, a new species is formed by a geographic separation of a small part of population from the mother population: this small founder population colonizes a new environment and it can evolve more rapidly. After enough time, the founder population and mother population are no longer interfertile if they meet again. In the words of Mayr:
“The major novelty of my theory was its claim that the most rapid evolutionary change does not occur in widespread, populous species, as claimed by most geneticists, but in small founder populations.” (Ibid.)
“(...) my conclusion was that a drastic reorganization of the gene pool is far more easily accomplished in a small founder population than in other kinds of population.” (Ibid.)
This was an implicit negation of ‘phyletic gradualism’ elaborated by Simpson. Allopatric speciation did not deny the biological concept of species of Dobzhansky based on isolating mechanisms and populations united by mutual fertility, but incorporated it into a new view, thus opening a debate: do new species arise from a population that changes or from small founder populations?
Punctuated equilibria: a revolution in biology
When Stephen Jay Gould and Niles Eldredge published Punctuated Equilibria: an Alternative to Phyletic Gradualism in 1972, they introduced a new question: if Mayr's geographic speciation is true, what are the consequences for the speed of evolution? It was like a bomb exploding in the scientific debate. Gould and Eldredge reversed the Synthesis' view applying the geographic speciation of Ernst Mayr to the interpretation of the fossil records. As they explained:
“The theory of allopatric (or geographic) speciation suggests a different interpretation of paleontological data. If new species arise very rapidly in small, peripherally, isolated local populations, then the great expectation of insensibly graded fossil sequences is a chimera. A new species does not evolve in the area of its ancestors.” 
This view on evolution leaves no room for missing links. Breaks in the fossil records reflect the actual geographic speciation over the generations. The fossil records also show the stasis in which founder populations found themselves after they adapted to a new environment. As Gould and Eldredge underline:
“The central concept of allopatric speciation is that new species can arise only when a small local population becomes isolated at the margin of the geographic range of its parent species. Such local populations are termed 'peripheral isolates'. A peripheral isolate develops into new species if isolating mechanisms evolve that will prevent the re-initiation of gene flow if the new form re-encounters its ancestors at some future time. As a consequence of the allopatric theory, new fossils species do not originate in the place where their ancestors lived.” (Ibid.)
In the theory of Gould and Eldredge, evolution proceeds from quantitative accumulation to qualitative leaps as is clearly recorded by the fossil records. It was a new way of reading the natural history of our planet: in other words, it gave a new tempo and new mode to evolution. Moreover, punctuated equilibria encompassed the previous theory of biological species and geographical species, not by rejecting them completely but by applying to these concepts a dialectical view. Small founder populations and different rhythms marked by fossil records: these are the ingredients of this revolutionary theory.
In the words of the two scientists:
“In summary, we contrast the tenets and predictions of allopatric speciation with the corresponding statements of phyletic gradualism previously given: 1) New species arise by the splitting of lineages; 2) New species develop rapidly; 3) A small sub-population of the ancestral form gives rise to the new species; 4) The new species originates in a very small part of the ancestral species' geographic extent - in a isolated area at the periphery of the range. These four statements again entail two important consequences: 1) In any local section containing the ancestral species, the fossil record for the descendant's origin should consist of a sharp morphological break between the two forms. The break marks the migration of the ancestral range. (...) 2) Many breaks in the fossil record are real: they express the way in which evolution occurs, not the fragments of an imperfect record.” (Ibid.)
After the publication of their first work, Gould and Eldredge were often accused of rejecting the core of Darwinism. On the contrary, they gave it a solid foundation. The theory of punctuated equilibria is based on natural selection because geographical speciation and the biological theory of species are based on natural selection. The new conditions (such as the potential lack of predators in the new environment) in which a small founder population finds itself give a boost to the rhythm of change.
Gould and Eldredge explained that fossil records can actually reflect episodes of acceleration in natural selection as well as the stability of species for long periods of time. Many years later, on the basis of new discoveries in the mechanisms of evolution, Gould and Eldredge were to extend the Darwinian core of natural selection from populations to species. In fact, punctuated equilibria is incompatible with the extrapolation of microevolution to macroevolution made by the Modern Synthesis: taxa formation from plants to mammals requires different mechanisms that are not reducible to microevolution that operates on populations. These mechanisms include natural selection, but they are not reducible to it. It is a pluralistic view of evolution based on a principle of emergent properties.
Dialectic and science
"It may also not be irrelevant to our personal preferences that one of us learned his Marxism, literally at his daddy's knee." – Gould
Within a few years, the theory of punctuated equilibria opened up a number of debates in palaeontology and evolutionary biology and proved to be a valid interpretation of the fossil record. For example, the traditional interpretation of the “Modern Synthesis” assigned too much time to the development of different phyla. Gould underlined this with irony:
“Thus, Durham tried to estimate the age of common ancestry for deuterostomes by stacking species end to end in lineages of phyletic gradualism. He specifies 6 m.y. as an average 'species duration' and estimates 100-600 durations strung on a line to reach the common ancestors of Early and Middle Cambrian echinoderms. Running further down the string, he places the common ancestors of deuterostomes 'slightly over a billion years before the beginning of the Cambrian' – an age considerably earlier than most generous estimates now being offered for the origin of the eukaryotic cell.” 
As we have noted, all scientists have an ideology that drives their work. The problem is they are not aware of it. Gould and Eldredge were conscious that they could never work out their theory without a specific conception of society. It is true that, over the years, Gould had reduced the political consequences of his theory in a situation where there was a general retrenchment by left-wing intellectuals. However, with this theory, these two scientists overturned the traditional view of evolution with a dialectical point of view. Gould and Eldredge always discussed the direct and indirect links between the dominant ideology and science. In 1981, Gould wrote one of his masterpieces entirely dedicated to this issue (The Mismeasure of Man). It is a wonderful example of how the dominant ideology can twist scientists' minds. But already in 1977 Gould and Eldredge emphasized that:
“The famous statement attributed to Linnaeus – natura non facit saltum – may reflect some biological knowledge, but it also represents the translation into biology of the order, harmony and continuity that European rulers hoped to maintain in a society already assaulted by calls for fundamental social change.” (Ibid.)
In 1977 they paid a direct tribute to Marx and Engels that is worth quoting in full:
“Karl Marx, who admired Darwin greatly and once stated that the Origin contained 'the basis in natural history for all our views' made the same point in a famous letter to Engels (1862):
“'It is remarkable how Darwin recognizes among beasts and plants his English society with its division of labour, competition, opening of new markets, invention, and the Malthusian struggle for existence. It is [Thomas] Hobbes' bellum omnium contra omnes [war of all against all] and one is reminded of Hegel's Phenomenology, where civil society is described as a spiritual animal kingdom, while in Darwin the animal kingdom figures as civil society.'
“We mention this not to discredit Darwin in any way, but merely to point out that even the greatest scientific achievements are rooted in their cultural contexts – and to argue that gradualism was part of the cultural context, not of nature.
“Alternate conceptions of change have respectable pedigrees in philosophy. Hegel's dialectical laws, translated into a materialist context, have become the official 'state philosophy' of many socialist nations. These laws of change are explicitly punctuational, as befits a theory of revolutionary transformation in human society. One law, particularly emphasized by Engels, holds that a new quality emerges in a leap as the slow accumulation of quantitative changes, long resisted by a stable system, finally forces it rapidly from one state to another (law of transformation of quantity into quality). Heat water slowly and it eventually transforms to steam; oppress the proletariat more and more, and guarantee the revolution.” (Ibid.)
The role of Stephen Jay Gould
The entire life of Stephen Jay Gould as a scientist was spent in developing the Darwinian theories of evolution and in enriching them with a dialectical method. It is not possible to deal here in a single article with his whole contribution to science but we want to point out that he succeeded in exposing the dialectical character of nature not ideologically, but by finding this character in the way nature concretely is. Criticizing the poor results of Ferdinand Lassalle as a theorist, Marx said: “He will discover to his cost that it is one thing for a critique to take a science to the point at which it admits of a dialectical presentation, and quite another to apply an abstract, ready-made system of logic to vague presentiments of just such a system” . The punctuated equilibria theory is such an achievement, a theory that does not impose dialectics on nature but honestly concludes that it is impossible to understand evolution without dialectics.
Scientists cannot isolate themselves from society. Although many of them seem to survive with a healthy although rough realism, they are vulnerable to the ruling ideology. This is obvious: in a class society, as the control of science is in the hand of the ruling class. This involves control over funding, over education plans, over recruiting and careers, over information and the media. It is not by chance that the recent discovery of the Higgs' boson was used to speak about God (“the discovery of the God particle”) as if the two things were somehow linked. Similarly, the view of evolution based on gradual changes in the gene frequencies was used to push the idea that everything is determined by genes: social differences, poverty, unemployment, illiteracy and so on. Rich people do better because they are the fittest to rule just like the survivor species in nature!
However, while most scientists think they can do without ideological and political ideas, and others embrace the status quo, there are also thinkers that embrace Marxism as a result of their research. As Engels pointed out many years ago, science proceeds in a dialectical manner. The ruling class cannot accept this, as dialectics means revolution in nature as in society. The theory of punctuated equilibria, giving a fundamental importance to sudden change, that is to revolutions, in nature is a direct attack on the ruling ideology. This is absolutely clear to those bourgeois ideologists that try to downplay its importance and who vilify Gould and Eldredge for their ideas.
Revolutions are rare events in nature as in society, but they mark entire epochs. That is why the analysis of revolutions is the most important task of science, whether we are talking about the Earth, the animals or humankind. Stephen Jay Gould had the merit of understanding this and of not being frightened by revolutions.
Thanks to him, our knowledge of animal evolution has made a tremendous leap forward. As Marxists, we are proud of the fact that this was achieved precisely because he was influenced by Marxist thinking. Brave intellectuals are important in helping us understand the world we live in. The working class armed with revolutionary ideas is required to change it.
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