History of evolutionism – post-neo-Darwinist period
It holds in general that it is not difficult to characterize a stream of thought, once it has ended. However, in the absence of a suitable temporal and personal distance, it is very difficult and perhaps impossible to describe a stream of thought that extends into the future or that is only forming at the present time. While I will attempt to do something of this sort in this chapter, I am aware of the danger that I could be completely mistaken. It is quite possible that future historians of science will consider the Post-Neo-Darwinist stream of thought to be a quite logical outcome of evolutionary synthesis and thus its integral component. Nonetheless, I am of the opinion that, at the very least for didactic reasons, it is useful to risk future loss of face and to attempt to define the currently emerging line of thought in respect to Neo-Darwinism.
Possibly with the exception of S. J. Gould, all the representatives of Post-Neo-Darwinism tended to consider or still consider themselves to be representatives of classical Neo-Darwinism. Nonetheless, some of their works have apparently exceeded the conceptual context of original evolutionary synthesis and have led or will in the future lead to a radical change in evolutionary paradigm. If we neglect the predecessors to which modern authors did not, at least consciously, refer in their thinking, i.e. the author of the model of shifting balances, Sewall Wright, and partly also the author of the concept of genetic revolution, Ernst Mayr, the first step in this direction was taken at the end of the 1960’s and beginning of the 1970’s by George C. Williams (1926-2010) (Williams 1966) and William D. Hamilton (1936-2000) (Hamilton 1964a; Hamilton 1964b), when they published their gene-centered concept of evolution. In their work, they implicitly assumed and clearly demonstrated on specific cases that, in studying a certain structure or a certain pattern of behavior, evolutionary biology must not ask how the particular traits provides an advantage for its bearer, but only how the particular trait provides an advantage for the allele that is responsible for its formation. Richard Dawkins (*1941) explicitly explained this idea and popularized it amongst the professional and lay public, originally in his popular-instructive book “The Selfish Gene” (Dawkins 1976) and subsequently in his professional work “The Extended Phenotype” (Dawkins 1982). He demonstrated that an individual cannot be an object of selection and that biological fitness cannot be a criterium of his success in sexually reproducing organisms. The object of selection must always be only a specific allele and the criterium of its evolutionary success is the increase in its frequency in comparison with the other alleles at the given locus. Works related to evolutionarily stable strategies, written jointly by John Maynard Smith (1920-2004) and George R. Price (1922-1975) (Maynard Smith & Price 1973), constituted another involuntary attack on the basic paradigm of Neo-Darwinism. These works, similar to the works of their successors, demonstrated that the criterium of success of a certain pattern of behavior and, in general, a certain biological trait is not how it increases or decreases the fitness of its bearer, but rather whether this corresponds to an evolutionarily stable strategy in the sense of game theory. They demonstrated that only a strategy that, once it predominates in the population, is capable of preventing the invasion of any other (even potentially more successful) minority strategy, has a chance from the long-term point of view. Taken to its logical conclusion, even the reproductive ability of the individual alleles is not the decisive criterium for their evolutionary success in a polymorphic population.
The work published by paleontologists Niles Eldredge (*1941) and Stephen Jay Gould (1941-2002) led to a further basic shift in the character of evolutionary biology. At the beginning of the 1970’s, these authors demonstrated that, contrary to expectations following from the Neo-Darwinist model of evolution, the evolution of species has a substantially discontinuous character (Eldredge & Gould 1972). Species mostly change only immediately after their formation and their existence is characterized by evolutionary stasis for a subsequent, incomparably longer time. Eldredge and Gould originally suggested that genetic homeostasis is basically responsible for evolutionary stasis and that genetic revolution (which occurs as a result of the founder effect (Mayr 1963)) is responsible for anagenetic changes, i.e. just those effects whose existence is directly connected with the competition of the individual alleles for an evolutionarily stable strategy. However, they later abandoned these ideas (see XXVI.5.3), possibly in connection with a certain tension present in the 1990’s between the representatives of American and British schools of evolutionary thought. Irregardless of the nature of the actual mechanism responsible for the punctuated character of evolution, this character in itself requires basic modification of the Neo-Darwinist concepts of the course of macroevolutionary events. As anagenesis is apparently closely coupled with cladogenesis amongst sexually reproducing organisms and selection can substantially affect the traits of organisms only at the moment of speciation, there has been a substantial increase in emphasis on other evolutionary mechanisms (species selection, interspecific competition, evolutionary trends driven by evolutionary constraints), whose effectiveness and importance in evolution (compared to selection) the Neo-Darwinists mostly doubted. Thus, evolutionary biology is, in a certain sense, returning to a plurality approach, which tended to be characteristic rather for the time of classical Darwinism and which was abandoned temporarily during the time of evolutionary synthesis (Gould 2002).