Evolutionary Theory from Darwin to Popper
Evolutionary Theory from Darwin to Popper
Carlo Maria Polvani
Why are there no penguins at the North Pole?
Despite the more than 150 years that have passed since the publication of Charles Robert Darwin’s (1809-1882) On the Origin of Species (1859), the debate on the theory of evolution is far from over. To better understand several scientific aspects of the ongoing discussion, it may be helpful to describe the general elements of the theory that are shared by the majority of the scientific community, distinguishing them from the specific positions held by the staunchest Darwinians.
The genetic makeup of every living being, namely the deoxyribonucleic acid (DNA) composing the genotype, is constantly subjected to mutation. In general, these changes do not result in advantages or disadvantages in that the majority of DNA mutations do not translate into changes in external characteristics, i.e., in phenotype. When, however, mutations cause more competitive characteristics to emerge, they tend to express themselves in subsequent generations by disruptive selection (one phenotype eliminates another), stabilizing selection (a phenotype is established in a population), or directional selection (the particular characteristic of a phenotype is strengthened). The succession of mutations which strengthen traits that are useful for survival induces the gradual divergence of a group which may possibly become the progenitor of a new species. This is illustrated by the following example.
Millions of years ago, perhaps driven by the search for food or to escape from predators, a species of bird settled permanently in the Antarctic. Over time, genotypic mutations took place in these birds. Most of these mutations remained dormant, but then came one which initiated the transformation of their wings into scaly fins. Subsequent mutations reinforced this phenotypic transformation. Little by little, the new birds, having lost the ability to fly, managed to survive in the harsh southern regions by becoming expert underwater divers, thanks to their new fins and an abundance of fish. The species which migrated to the South Pole millions of years ago is no longer seen there today. Instead, there is a new one: the pen- guin.
On the basis of fossil finds, great naturalists like Jean-Baptiste de Lamarck (1744-1829) — who had formulated a thesis on evolution a century before Darwin — had already defended general evolutionary theories. The theory introduced by Darwin, the biologist from Shrewsbury, postulated — as Jacques Monod explained in Le hasard et la necessité (1970), reinterpreting the line by Democritus: “Everything existing in the universe is the fruit of chance and necessity” — that there were two, and only two, forces to explain the phenomenon of evolution: that of chance, which creates diversity at the genotypic level, and that of selection, which supports the emergence of the phenotypes most likely to guarantee survival.
At the start of the 21st century, in spite of considerable internal disputes in the Darwinist camp on the subject of natural selection — the gene, according to Clinton Richard Dawkins; species, according to Stephen Jay Gould (1941-2002); and social behaviour, according to Edward Osborne Wilson — Darwinism’s line of demarcation actually rested on the refusal to concede any exception to the principle supporting the exclusive binomial of chance and necessity.
In The Blind Watchmaker (1986), Dawkins — while warning that necessity is a deterministic rule, which could be measured were it possible to identify the factors, whereas chance is a completely unpredictable force, therefore totally unforeseeable — identifies, in the interaction between these two absolutely autonomous forces, — the unique, necessary and convincing explanation of the phenomenon of life on earth. He demonstrates the merits attributed by modern Darwinism to this line of demarcation which, as Monod wrote, must be accepted in its rough dramatic nature, despite “the unwearying, heroic effort of mankind desperately denying its own contingency”.
In universities throughout the world, observations are being analyzed which could indirectly invalidate or confirm Darwinian positions. Could self-replicating chemical molecules, perhaps, be at the origin of life? Why is there a universal genetic code? Is the statistical incidence of chance mutations of a genotype likely to produce adequate phenotype diversity? How can one explain the Cambrian explosion, the event which, 530 million years ago, saw a temporary increase — by an order of magnitude — in the appearance of animal species? But any calling into question of the chance-necessity axiom is unpopular, to the point of being quickly labelled as crypto-creationism of a religious fundamentalist stamp, as happened when the founders of Intelligent Design introduced the concepts of irreducible complexity, defended by biochemist Michael Behe in Darwin’s Black Box (1996), and those of specific complexity advocated by mathematician William Albert Dembski in The Design Inference (1998).
This is not the place to debate the validity of their propositions, but it is impossible not to note that there exists in the academic world a certain reluctance to subject Darwin’s theory to the “logic of falsification” introduced by Karl Popper (1902- 1994). This Austrian-British philosopher, inspired by the work of mathematician Alfred Tarski (1901- 1983), had noted as early as the 1930s the fundamental asymmetry between the verifiability and falsifiability of scientific theories: no matter how consistently experimental observations may support a hypothesis, actually, one single unfavourable piece of evidence is sufficient to refute it.
Thus, according to Popper, what allows a theory to bear the title ‘scientific’ depends on an experiment capable of producing evidence that might refute it. Popper himself examined the scientific nature of evolutionary theory in light of his own criteria and still today, it is debatable as to whether he had expressed his definitive opinion. Therefore, it is still fair to ask whether there exists an experiment capable of contesting the postulate that chance and necessity are the only forces at play in the origin and selection of species. In answer to this query, Dawkins replied that the simple observation of any animal is enough, such as the hippo for instance. But the specific example of the penguin shows that this position does not seem tenable.
The Darwinist position implies that statistically, the genotypic mutation of wings into fins would have also occurred in birds living in other areas on the planet, such as, for example, the rainforests of Sumatra, but since in that environment the phenotypic features offered no competitive advantages, the penguin did not establish itself there. The same Darwinist position, however, implies that in the Arctic zones, similar in many ways to those of the Antarctic, species similar to the penguin might have been expectcd. Instead, there are none. To explain this absence, many Darwinists frequently use a deductive or ‘top-down’ approach, pleading the existence of causes not yet explained experimentally in order to justify an unforeseen observation.
There would be no lack of Darwinists prepared to support the idea that the presence of predators like polar bears, who live exclusively at the North Pole, could possibly be the reason for the absence of penguins in the boreal zones. Although, this line of argument might even prove valid could such an experiment take place, it is nevertheless tainted by a tautological logic: in fact, one cannot base a theory on an observation and then, when such a process results in an unsatisfactory conclusion, invoke the theory to justify the observation. This limitation is reinforced by the fact that, as things stand now, the Darwinist position, contrary to other scientific theories, has nothing to brag about with regard to predictability, that is, the capacity to correctly predict future observations on the basis of theoretical postulates. Indeed, there is not a single biologist who can forecast if and when penguins might appear at the North Pole, not even assuming the hypothetical extinction of polar bears due to global warming. A reading of John Paul Il’s 1996 Message to the Pontifical Academy of Sciences is enough to realize that few today doubt the evolution of life on Earth. This, however, does not alter the fact that the onus probandi (burden of proving) the precise scientific merit of the specifics of the Darwinist formulation of that theory still rests on the shoulders of its defenders.
In this context, it is rather paradoxical that proponents of scientific independence from the interference of religion — atheistic vehemence is manifest in Dawkins’ pamphlet The God Delusion (2006) — refuse to submit their thesis to a strictly scientific examination. Hence, merit goes to the Pontifical Academy of Sciences for having rigorously investigated, in 2008, the scientific basis of the evolution of life. The main threat to the scientific integrity of the theory of evolution, in fact, does not come from an alleged invasion of the field by theology, but rather from the incapacity of a certain self-referential science to recognize when it is time for a paradigmatic change, as philosopher Thomas Samuel Kuhn (1922-1996) indicated in The Structure of Scientific Revolutions (1966), noting ironically that “only when they must choose between competing theories do scientists behave like philosophers”.
L'Osservatore Romano
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6 February 2015, page 13
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