Evolution and Human Choice over Time

Evolution and Human Choice over Time Alan R. Rogers” 1997 1 The connection between evolution and economics In economics, equilibria are often found by equating two versions of the marginal rate of sub- stitution (MRS). For example, my MRS in preferences (the ratio at which I am “just willing” to exchange two goods) should equal the MRS in exchange (the ratio at which I can exchange them in the market). Otherwise, I would have reason to sell one good and buy the other. At equilibrium (as shown in figure 1) these two versions of the MRS must be equal. This analysis is also familiar to evolutionary ecologists, as shown in figure 2. There, the indif- ference curves are replaced by fitness isograms, which connect points of equal Darwinian fitness.! In place of a budget constraint, ecologists study a variety of other constraints. The principle, how- ever, is the same: equilibrium occurs at the point where the two curves have equal slope. These two forms of analysis are connected by something deeper than analogy. They are con- nected by a third equilibrium principle, which was first described by Hansson and Stuart [12]. These authors define the MRS in fitness as the ratio at which two goods can be exchanged without affecting Darwinian fitness. Thus, the MRS in fitness measures the absolute slope of the dotted lines in figure 2. The new equilibrium principle asserts that, at evolutionary equilibrium, the MRS in fitness must equal that in preferences. A simple proof of this principle is shown in figure 3. The new equilibrium principle adds an additional equation to the arsenal of economics. The MRS in preferences must now equal that in fitness as well as those in exchange and production. If the hypothesis of evolutionary equilibrium turns out to be useful, then this should allow a more powerful theory of economics. *Research Centre, King’s College, Cambridge CB2 1ST, U.K. Present address: Dept. of Anthropology, University of Utah, Salt Lake City, UT 84112, U.S.A. Published as pp. 231-252 in Characterizing Human Psychological Adaptations, edited by G. Bock and G. Cardew. CIBA Foundation Symposium 208. John Wiley and Sons. 'Tn models with discrete generations, Darwinian fitness is the conditionally expected number of an individual’s offspring, given its genotype. In models with overlapping generations, fitness is measured by R. A. Fisher’s [8] “Malthusian parameter,’ which measures the asymptotic rate of exponential increase in the numbers of one’s descen- dants [2]. HOUSE_OVERSIGHT_011155