According to Peirce’s cosmological hypothesis, evolution is a continuing process of growth which accounts for both the diversity and the regularities we observe in a universe both mental and physical.
The regularities or ‘laws’ of nature result from the habit-taking tendency, which tends toward the extreme ‘crystallization’ of form which in physics we call ‘matter.’ But the behavior patterns of the physical universe are never completely determinate, the laws of nature never absolutely exact, because the habit-taking tendency is countered and complemented by a spontaneity which keeps the universe alive and accounts for the growing diversity and complexity of forms. This spontaneity is primal to the mental side of evolution, which involves both taking and breaking habits.
Here is Peirce’s explanation of the ‘Uniformity’ of nature in Baldwin’s Dictionary:
The hypothesis suggested by the present writer is that all laws are results of evolution; that underlying all other laws is the only tendency which can grow by its own virtue, the tendency of all things to take habits. Now since this same tendency is the one sole fundamental law of mind, it follows that the physical evolution works towards ends in the same way that mental action works towards ends, and thus in one aspect of the matter it would be perfectly true to say that final causation is alone primary. Yet, on the other hand, the law of habit is a simple formal law, a law of efficient causation; so that either way of regarding the matter is equally true, although the former is more fully intelligent. Meantime, if law is a result of evolution, which is a process lasting through all time, it follows that no law is absolute. That is, we must suppose that the phenomena themselves involve departures from law analogous to errors of observation. But the writer has not supposed that this phenomenon had any connection with free-will. In so far as evolution follows a law, the law of habit, instead of being a movement from homogeneity to heterogeneity, is growth from difformity to uniformity. But the chance divergences from law are perpetually acting to increase the variety of the world, and are checked by a sort of natural selection and otherwise (for the writer does not think the selective principle sufficient), so that the general result may be described as ‘organized heterogeneity,’ or, better, rationalized variety. In view of the principle of continuity, the supreme guide in framing philosophical hypotheses, we must, under this theory, regard matter as mind whose habits have become fixed so as to lose the powers of forming them and losing them, while mind is to be regarded as a chemical genus of extreme complexity and instability. It has acquired in a remarkable degree a habit of taking and laying aside habits. The fundamental divergences from law must here be most extraordinarily high, although probably very far indeed from attaining any directly observable magnitude. But their effect is to cause the laws of mind to be themselves of so fluid a character as to simulate divergences from law. All this, according to the writer, constitutes a hypothesis capable of being tested by experiment.
— Peirce, BD ‘Uniformity’ (1901)
Peirce says here that ‘the law of habit’ – as opposed to the ‘fundamental law of mind,’ which is the tendency of all things to take habits – ‘is a simple formal law, a law of efficient causation.’ Ten years earlier, in ‘The Doctrine of Necessity Examined,’ Peirce had written that the necessitarian, while believing that irregular events are inexplicable, also says
that the laws of nature are immutable and ultimate facts, and no account is to be given of them. But my hypothesis of spontaneity does explain irregularity, in a certain sense; that is, it explains the general fact of irregularity, though not, of course, what each lawless event is to be. At the same time, by thus loosening the bond of necessity, it gives room for the influence of another kind of causation, such as seems to be operative in the mind in the formation of associations, and enables us to understand how the uniformity of nature could have been brought about.
W8:123, CP 6.60
This ‘other kind of causation’ is called by Jesper Hoffmeyer semiotic causality, which ‘gives direction to efficient causality, while efficient causality gives power to semiotic causality’ (Hoffmeyer 2008, 64). This duality or complementarity of causes accounts for the two sides of evolution, the physical and the psychical or mental.
Semiotic causality is implicit in Peirce’s definitions of ‘sign,’ which generally follow the path of determination object > sign > interpretant:
I will say that a sign is anything, of whatsoever mode of being, which mediates between an object and an interpretant; since it is both determined by the object relatively to the interpretant, and determines the interpretant in reference to the object, in such wise as to cause the interpretant to be determined by the object through the mediation of this ‘sign.’
EP2:410
The reverse side of this path of determination is a path of representation: the sign represents the object to the interpretant, which then represents the sign – by determining another interpretant sign, or else a ‘habit-change,’ which is both an end of semiotic causality and a governor of efficient causation, i.e. a determinant of future transformations in the physical realm. Any actual occurrence of semiotic determination/representation must itself determine and represent a change in a state of mind, quasi-mind or bodymind: in other words, it must make a difference to that bodymind, and this difference is both semiotically and efficiently caused.
In other words, the logical interpretant of a sign, as a ‘habit-change’ or modification of the guidance system which ‘gives direction’ to the subsequent practice of the guided system or bodymind, will determine the energetic interpretants of future signs, which over time will make the path of practice by walking it. This in turn will make a difference to the physical (as well as the mental) context of further semiosis.
In terms of evolutionary biology, the way a type of organism interacts with its environment can effect changes in both organism and environment, which may in turn affect the ability of the species to be represented in another generation of organisms. Over time, then, natural selection will weed out the ethos which does not maintain its viability as an occupant of its ecological niche. But natural selection must have a variety of possibilities to select from, and does not in itself account for that variety. Hence the need for the hypothesis that spontaneity or ‘chance’ is a primal element in an evolving universe such as the one we all inhabit.