In 1891 C.S. Peirce wrote in an article with the title “The Architecture of Theories," "Now Philosophy Requires Thoroughgoing Evolutionism of None” (Peirce, 1958: 148). For Peirce a radical evolutionism would make it possible to found a new philosophy of nature that could substitute exclusively physico-mathematical models: “Now the only possible way of accounting for the laws of nature and uniformity in general is to suppose them results of evolution. This supposes them not to be absolute, not to be obeyed precisely. It makes an element of indeterminacy, spontaneity, or absolute chance in nature” (Peirce, 1958: 148). Peirce linked this to the question of life: “In admitting pure spontaneity or life as a character of the universe, acting always and everywhere though restrained within narrow bounds by law, producing infinitesimal departures from law continually [...], I account for all the variety and diversity of the universe, in the only sense in which the really sui generis and new can be said to be accounted for” (Peirce, 1992: 308).
Here, nature is no longer a spatial ensemble that is subdivided into domains and that will be occupied by already made beings; it is rather made by spontaneous geneses and emergences; it is made by endless variations that are reciprocally linked to one another. New existences add themselves to ancient ones. The uniformity and the laws of nature can no longer be looked for in general a priori principles that would realize themselves in various ways. They are rather produced by relations between individuals that negotiate their respective survivals. This point is fundamental, as it marks the rupture of Peirce, and thereby of the pragmatists in his succession, with any linear vision of evolution that would be guided by and oriented towards a final cause. Peirce calls for an “evolutionism” without a final cause, without a continuous trajectory, an “evolutionism” made by contingencies and variations. The human then appears neither as its achievement nor as its model; it is rather an event that takes place at the intersection of a plurality of series of variations and selections. William James took up this idea of a universe in evolution in his Principles of Psychology. According to James the nervous centers “[l]ike all other organs, […] evolve from ancestor to descendant” and emotions are comparable to species in Darwin: “The trouble with the emotions in psychology is that they are regarded too much as absolutely individual things. So long as they are set down as so many eternal and sacred psychic entities, like the old immutable species in natural history, so long all that can be done with them is reverently to catalogue their separate characters, points, and effects. But if we regard them as products of more general causes (as "species" are now regarded as products of heredity and variation), the mere distinguishing and cataloguing becomes of subsidiary importance” (James, 1950: 449). This is an evolutionism applied to all the parts of the body that James is interested in and that finds its prolongation in Dewey’s analysis of living as well as social forms of organization. In the philosophy of nature (Peirce and Whitehead), the social sciences (Dewey and Mead) traversing the field of psychology (with James) a real synthesis and generalization of evolutionary theories is appointed, producing a rupture with the principal philosophies of life such as vitalism, functionalism, or neo-finalism.
This research project comprised of three axes: first of all it aimed for a rereading of the pragmatist enterprise from the point of view of its evolutionary inheritance (Lamarck, Darwin, and Spencer). The major questions that constitute pragmatist philosophy (the theory of knowledge, the “functionalist” method, and the theory of experimentation) were then reinstalled in the context of an evolutionary approach. Secondly, by this way it was possibly to analyze the manner by which an ensemble of scientific theories circulates in philosophy and how they transform when undergoing the generalizations conducted on them. Finally, this project sought to unfold certain epistemological implications of evolutionary theories. The pragmatists insisted on the fact that our theories of knowledge had been constructed in taking the physical world as their model, and that they were thus inadequate for the interpretation of an evolutionary reality. This question of a transformation of models of knowledge towards biological realities remains of vital importance today.