Skip to main content

Darwinism and the Theory of Rational Choice

Final Report Summary - DARTCH (Darwinism and the Theory of Rational Choice)

The overall aim of the research project was to explore the connections between Darwinian evolutionary theory and the theory of rational choice, from an overarching philosophical perspective. The starting point of the project, and the main motivation for conducting an extended philosophical enquiry, was the existence of deep and interesting connections, conceptual and formal, between evolutionary biology and rational choice theory. At root, these connections arise because a notion of optimisation, or maximisation, is central to both bodies of theory. Evolutionary biologists typically assume that because of natural selection, animals will behave as if they are trying to maximise their Darwinian fitness (for some appropriate measure of fitness). This is the guiding assumption in much work on animal behaviour. Rational choice theorists typically assume that humans will behave as if they are trying to maximise a utility function. This is the guiding assumption in much work in social science. Thus there is a close parallel between the notion of fitness in evolutionary theory and the notion of utility in the theory of rationality. However, despite this parallel, we have found that, in a range of situations, Darwinian evolution can give rise to behaviour which appears to violate the canons of traditional rational choice theory. Thus the idea that biologically optimal behaviour and rational behaviour will automatically coincide needs to be treated with caution.

Two important philosophical morals emerge from this conclusion. The first concerns the practice, common among evolutionary biologists, of treating evolved organisms as if they were rational agents trying to achieve a goal, and applying intentional descriptors to them ("wants", "tries, "believes"), in a metaphorical sense. The heuristic power of this "organism as rational agent" approach to biological evolution is considerable, and some evolutionists have argued that it follows from Darwinian first principles. Our results, however, suggest that the organism-as-rational idea has its limitations. There is a strong temptation to regard the idea as virtually a definitional truth, or an obvious consequence of the basic logic of natural selection (“survival of the fittest”); however this temptation should be resisted. At root, the selective preservation of favoured variants in a population, which is what Darwinian evolution boils down to, does not necessarily produce organisms that behaviour like rational agents trying to achieve a goal.

The second moral concerns the old question of anthropomorphism in evolutionary biology. The idea that evolved organisms are "trying" to achieve a goal, such as survival and reproduction, and have phenotypic traits which further that goal, is a mainstay of evolutionary biology. However the idea is controversial. Some regard it as an unjustified extrapolation of an idiom, whose literal application is to deliberate human action, to non-human organisms. Others regard it as fully justified, a valid expression of the Darwinian idea that natural selection will optimise organisms’ phenotypic traits, including their behaviour, and serving to pick out a real pattern in the natural world. Our results suggest that the truth lies between these two extremes. On the one hand, the use of rationality-inspired models in evolutionary biology has borne genuine intellectual fruit, and does pick out a real phenomenon in nature. On the other hand, there is no a priori guarantee that evolved organisms, whose behaviour has been optimised by natural selection, will behave like rational agents trying to achieve a goal, and counterexamples to this hypothesis can be constructed. Thus there is no valid general argument, from evolutionary first principles, for the conclusion that the behaviour of evolved organisms can be described in rational terms, despite what many authors, in philosophy and in biology, have thought.