منشا ابزار: انتخاب جنسی و مصرف آشکار

This paper proposes an explanation for the universal human desire for increasing consumption and the associated propensity to trade survival opportunity off conspicuous consumption. I argue that this desire was moulded in evolutionary times by a mechanism known to biologists as sexual selection, whereby an observable trait – conspicuous consumption in this case – is used by members of one sex to signal their unobservable characteristics valuable to members of the opposite sex. It then shows that the standard economics problem of utility maximisation is formally equivalent to the standard biology problem of the maximisation of individual fitness, the ability to pass genes to future generations, and thus establishes a rigorous theoretical foundation for including conspicuous consumption in the utility function.

Homo Economicus’s utility function constitutes one of the fundamental building block of economics. Its canonical form hinges on two assumptions: that there are trade-offs among the available commodities and that its shape is independent of the budget constraint. The latter implies that choices result from the interaction between income/wealth/resources, which are variable, and preferences, which are fixed. The trade-offs between goods implies that individuals are willing to sacrifice survival enhancing activities, such as the acquisition of nutritious food, of adequate shelter, of health care, to acquire goods with zero or negative survival value like luxury goods, leisure travel, entertainment, and so on. More succinctly, conspicuous consumption for its own sake enhances utility. This standard economics assumption clearly tallies with evidence, but the lack of a theoretical justification for it perplexes other scientists: “Western economics usually assumes that individuals are out to maximise personal gains, but where is the scientific justification for this assumption? And what exactly is ‘personal gain’?” ( Trivers, 1985, p. 1). Trivers’ doubts are spelled out more explicitly by Grafen (1998, p. 441): “The formulation of the dynastic utility function in terms of consumption purely for its own sake is inconsistent with the biological viewpoint”. The inconsistency is the apparent lack of any fitness advantage, which any physical or behavioural trait must afford in order to develop and persist in a population. 1 In this paper I propose a foundation for the human propensity to trade survival opportunities off conspicuous consumption for its own sake rigorously based on evolutionary arguments, and therefore consistent with the biological viewpoint. The universality of the desire for conspicuous consumption across cultures and continents and the view of evolutionary psychology regarding the speed of adaptations (Barrett et al., 2002, p. 12) indicate that this trait was hard wired in the brain of early humans prior to their dispersion from Africa, and therefore must have provided evolutionary advantages in the conditions prevailing between one million and 80,000 years ago. I build on the established economics tradition which explains features of human behaviour through evolutionary lenses by looking for fitness advantages of these features. Alchian (1950, pp. 213–214) and Friedman (1953) viewed profit maximisation as a selection mechanism for firms. More recently, evolutionary advantages have been suggested for many human traits.2 My viewpoint, however, differs from most of the literature in that the fitness advantage of the trait considered is not the enhanced survival chances of the individuals with the trait: indeed individuals with a stronger desire for conspicuous consumption for its own sake had a survival disadvantage, relative to individuals with a weaker desire. They, however, also had a reproductive advantage, which more than offset their survival disadvantage. Thus the trait became established in the human genotype, as the genes linked to the trait became more frequent as generations went by. In the jargon, conspicuous consumption is a signal that causes sexual selection by mate choice. This is an evolutionary mechanism by which individuals of one sex signal their unobservable quality to the opposite sex, and their reproductive success depends on the signal via the mating choice of the individuals of the opposite sex. This mechanism is the driving force for the development of traits which are differentiated by sex and have negative survival value 3: from the extravagant plumage of pheasants, paradise birds, peacocks and many other birds, to the ritual dancing and hopping displays in “leks”, to the courtship vocalisations in tigers, deer, crickets, frogs, to the flashing of fireflies, to the complex bowers built and decorated by bowerbirds; to human traits such as the male beard and the female breasts. 4 Zahavi (1975) realised that males’ signals must be costly, exactly in the sense in which signals are costly in the economics literature (Spence, 1973): the higher an individual’s quality, the less burdensome it is for him to incur the cost of the signal, and the stronger the signal he will issue to distinguish himself from his lesser rivals in the eye of the females. His explanation of sexual selection was given a solid game-theoretic foundation by Grafen, 1990a and Grafen, 1990b. Consumption for its own sake, conspicuous consumption, I argue here, is precisely such a signal. It is easy to observe and expensive to acquire. It has served, throughout history, as an indicator of an individual’s desirability as a mate. Veblen (1899) identified clearly the importance of expensiveness and wastefulness of conspicuous consumption: inexpensive items are not, cannot be effective signals, precisely because their very inexpensiveness makes it possible for everyone to sport them. 5 Unlike Veblen, recent economic analysis has had access to Fisher’s and Zahavi’s insights, and yet has neglected the role of sexual selection as a powerful engine of human evolution. 6 The signalling model in Section 2, closely inspired by Grafen, 1990a and Grafen, 1990b, captures these ideas. It describes a population composed of males and females where the males’ reproductive potential is limited by female choice. Males differ in their value to females, and face a trade-off between wasteful “conspicuous” consumption and unobservable activities which enhance their chance of survival. Females observe males’ conspicuous consumption and choose with whom to mate. In a separating equilibrium, males undertake conspicuous consumption in order to signal their quality to females, and females are more likely to mate with males whose observed consumption is higher. Proposition 1 in Section 3 identifies some conditions on the population and the environment which ensure that a separating equilibrium exists. The core of the paper is Section 4. Here I show the natural connection between maximisation of fitness and maximisation of a utility function with consumption bundles as arguments. The trade-off between survival and reproduction is mapped one-to-one with the trade-off between “survival activities” and “conspicuous consumption”. This provides an evolutionary foundation to the indifference maps that constitute the basis of the economic analysis of consumer behaviour, suggesting that preferences are not arbitrary, but have evolved in response to our ancestors’ exogenous constraints. Section 5 discusses some empirical evidence and considers some open economics questions in the light of the ideas of the paper, and Appendix A presents the formal proof of Proposition 1.

This paper views a utility function with trade-offs between consumption for its own sake and survival activities as hard wired by evolutionary pressure exerted by sexual selection. It therefore links Grafen, 1990a and Grafen, 1990b Grafen’s (1990a,b) analysis of the role of sexual selection in shaping the genome with the work, by Robson and others, on the evolutionary foundations of utility functions (Robson, 2001a, and the references cited in footnote 2). The hard-wiring mechanism is discussed briefly in Section 5.1, and the paper ends with some empirical evidence, necessarily somewhat heuristic in nature, and with the interpretation in the light of the ideas proposed here of some aspects of human behaviour that economists have typically found difficult to reconcile with the standard optimising model.