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.
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 The Origin
There is a grandeur in this view of life – Charles Darwin
When Charles Darwin in 1859 published his masterpiece, The origin of the species by means of natural selection, many attempts to introduce an evolutionist view of life had already been made by Diderot, Maupertuis, 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 were conisdered 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.
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 Copernicus and Galileo 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's 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. Steve 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 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 a nutshell, 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 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 basically 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 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 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. Marx and 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.