One of the changes in biological thinking brought on by Darwinism is the replacement of the typological thought of the morphological rationnalists by the "population thinking" of the current neo-Darwinist synthesis.
Traditional Biology seeks to be a science of forms. The Linnean hierarchy, which is more empirical that rational, seeks to classify forms through a structure of nested classes (taxa) of the traditional, Aristotelian kind, whose members are individual organisms. In this system, a "higher" taxon can be said to be more 'abstract' in relation to a lower one, requiring fewer properties for membership and with a greater extension. But according to Driesch, the Linnean hierachies of genera and species were only related on the basis of empirical abstraction, not on the kind of fundamental concepts that carry principles of division and allow for a rational systematics. In the latter case, according to Driesch, "The so-called ' genus' ... then embraces all its 'species' in such a manner that all peculiarities of the species are represented already in properties of the genus." (The Science and Philosophy of the Organism, p.245)
While from a Darwinian perspective, forms can only be unified in terms of their historical genesis, this is not the case from the perspective of a rational systematics -- whose central concept is that of homology. The claim of a rational system of forms is that in a developed rational system of forms, what actually happened in history would become of relatively minor interest. But the concept of form in such a science would be the result of a dialectic between a rational systematics ( morphology) and an explanatory theory of morphogenesis. (Webster, Form and Transformation, p. 124)
For Cuvier, the concept of 'type' was, in the first place, a principle of classification. (see Cassirer, The Problem of Knowledge p. 128 ff.) Cuvier's idea of the type served to advance Kant's thesis of the irreducible coherence of part and whole that constitutes the essence of organic nature, and that the organism is no mere collection of parts, for even in its separate parts we can find the form of the whole. According to Cassirer, here the type is not a real object but a ' model' (an instrument of thought) of invariant relations, initially constructed by abstraction from concrete individuals. By means of this model, organisms can be compared and related through an approach that considers the diversity of natural forms as if they had been constructed on the basis of a restricted number of common structural plans. (for issues of type, see mapping and natural form) For Cuvier, type was an expression of definite and basic relationships in the structure of living beings that are fixed and inalterable and upon which all knowledge of them depends. Cuvier actively rejected theories of evolution For Cuvier, the internal consistencies of type follow rules no less inviolable than the purely ideal figures of geometry. Just as every property of a geometrical figure, such as a circle or a parabola, can be employed to derive its analytic equation, and the equation in turn can lead to all other properties of the curve, so a similar process of derivation connected every feature of living organisms with the concept of the type.
For Karl Ernst von Baer, the father of modern embryology, development is not merely from the general to the specific, but takes place within the bounds imposed by type, (which he defined as "the positional relationship of the inherent elements and the organs." in which characters of the larger classificatory group appear before those of the species and individual. And if embryos of higher animal forms ressemble those of lower, they only ressemble the embryos, not the adult forms. Thus the surest way of determining true homologies of parts will be to study their early development.
Critics of neo-Darwinism point out that scientist still rely on their ability to identify specimens as types, and that Darwinism has looked only on the conditions of evolution while overlooking its actions.
Michael Polanyi stresses the unspecifiability of morphological observation and the identification of normal shapes, not to discredit the activity, but to underscore the importance of what he calls "personal knowledge," a "fateful obligation to form expectations on necessariy insufficient evidence." Polanyi celebrates the "committment" of increasing consciousness in much the way Teilhard de Chardin described the emergence of a "noosphere." Like Teilhard, Polanyi believes that the emergence of life and the creative methods of biology are a model for a philosophy of learning, a "panorama of emergence" which Polanyi calls "ultra-biology."
The shift to population thinking in contemporary biology is a result of Darwin's stress on geneaology, on descent from a "common ancestor" as the principle of classification. For Darwin, "propinquity of descent (is) the only known cause of the similarity of organic beings." (Origin of Species, p.399) In the "Neo-Darwinian Synthesis." random mutation at the genetic level is subject to natural selection and leads to branching phylogenies converting varieties within populations to variation between populations (see evolution) Variation or diversity among individuals in a population provides a basis for competition during natural selection. Variation in the reproductive success of one individual relative to another is essential for natural selection to occur. Ernst Mayr rejects typological thinking altogether and calls species "groups of interbreeding natural populations that are reproductively isolated from other such groups." (1969, p.26) The basic question of population genetics (posed by R.M. Fisher at Cambridge in 1930)is whether slight selective advantages acting over long times could mold and renew populations. Could a single mutant gene which conferred a very slight selective advantage over the normal, or wild-type, gene and which arose in a single individual in a breeding population, spread throughout the population by virtue of the selective advantage it afforded? (see Kauffman, Origins of Order, pp 8-9)
Ernst Mayr espouses an extreme form of empiricism. As he explains:"The assumptions of population thinking are diametrically opposed to those of the typologist. The populationist stresses the uniqueness of everything in the organic world. What is true for the human species -- that no two individuals are alike -- is equally true for all other species of animals and plants. All organisms and organic phenomena are composed of unique features and can be described collectively only in statistical terms. Individuals, or any kind of organic entities , form populations of which we can determine only the arithmetic mean and statistics of variation. Averages are merely statistical abstractions; only the individuals of which the population is composed have reality. The ultimate conclusions of the population thinker and of the typologist are precisely the opposite. For the typologist the type, (eidos -- which is usually translated as form) is real and the variations illusion, while for the populationist the type (average) is an abstraction and only the variation is real. No two ways of looking at nature could be more different." ( Animal Species and Evolution, p. 5, quoted in Webster and Goodwin, Form and Transformation. )
As Gerry Webster points out, all comparisons require general terms, or terms of kind. If individuals were as "unique" as Mayr claims, they would possess no common properties at all. If a research programme for Biology minimized the importance of such regularites, it would bring that science to a dead stop. (p.28) Webster claims that the activity of populationist thinking is to create abstract metriomorphs, such as the model of the human family which consists of 2.63 (metriomorphic) children. (see homology for another concept contested between neo-Darwinists and new morphologists)
The study of artifical life assumes that it is possible to organize a population of machines in such a way that their interactive dynamics is "alive."