Arthur J. Robson

The emergence of humans: The coevolution of intelligence and longevity with intergenerational transfers

Two striking differences between humans and our closest living relatives, chimpanzees and gorillas, are the size of our brains (larger by a factor of three or four) and our life span (longer by a factor of about two). Our thesis is that these two distinctive features of humans are products of coevolutionary selection. The large human brain is an investment with initial costs and later rewards, which coevolved with increased energy allocations to survival. Not only does this theory help explain life history variation among primates and its extreme evolution in humans; it also provides new insight into the evolution of longevity in other biological systems. We introduce and apply a general formal demographic model for constrained growth and evolutionary tradeoffs in the presence of life-cycle transfers between age groups in a population.

The Evolution of Human Life Expectancy and Intelligence in Hunter-Gatherer Economies

The economics of hunting and gathering must have driven the biological evolution of human characteristics, since hunter-gatherer societies prevailed for the two million years of human history. These societies feature huge intergenerational resource flows, suggesting that these resource flows should replace fertility as the key demographic consideration. It is then theoretically expected that life expectancy and brain size would increase simultaneously, as apparently occurred during our evolutionary history. The brain here is considered as a direct form of bodily investment, but also crucially as facilitating further indirect investment by means of learning-by-doing.

Why Would Nature Give Individuals Utility Functions

Consider the possible biological origin of the expected utility criterion. On the one hand, if individuals possess a utility function stemming from the rate of production of expected offspring, they can rapidly adapt to arbitrary unknown distributions in a bandit problem. Embedding such a utility function in a simple rule of thumb involving no beliefs about probabilities leads to evolutionary optimality. On the other hand, if any rule whatever yields evolutionary optimality for all distributions, this precise utility function must be implicit, in a revealed preference sense.

Evolution and Human Nature

This paper considers how biological evolution shaped the elements of a simple but complete model of economic decision making. These elements are preferences, beliefs and rationality. Whereas Nature might impose preferences over consumption on the individual, Nature might optimally allow beliefs to be influenced by local knowledge and final choice to be flexible. This reinforces the usual approach. On the one hand, evolution also suggests that some extensions of this model are implausible; on the other, it suggests unexpected directions of generalization. In any case, evolution provides a basis for an overarching economic theory and maintains restrictions on this theory.

The Existence of Subgame-Perfect Equilibrium in Continuous Games with Almost Perfect Information: A Case for Public Randomization

The starting point of this paper is a simple, regular, dynamic game in which a subgame-perfect equilibrium fails to exist. Examination of this example shows that existence would be restored if players were allowed to observe the output of a public-randomization device. The main result of the paper shows that the introduction of public randomization yields existence not only in the example but also in a large class of dynamic games. It is also argued that the introduction of public randomization is the minimal robust extension of subgame-perfect equilibrium in this class of games. Copyright 1995 by The Econometric Society.

The Evolutionary Foundations of Preferences

Abstract This paper surveys recent work on the evolutionary origins of preferences. We are especially interested in the circumstances under which evolution would push preferences away from the self-interested perfectly-rational expected utility maximization of classical economic theory in order to incorporate environmental or social considerations. JEL Codes: D0, D8

Insurance as a Giffen good

Abstract Can insurance be a Giffen good? This can never happen if the coefficient of relative risk aversion is less than or equal to one. If this coefficient is greater than one it is possible but not empirically plausible.

We age because we grow

Why do we age? Since ageing is a near-universal feature of complex organisms, a convincing theory must provide a robust evolutionary explanation for its ubiquity. This theory should be compatible with the physiological evidence that ageing is largely due to deterioration, which is, in principle, reversible through repair. Moreover, this theory should also explain why natural selection has favoured organisms that first improve with age (mortality rates decrease) and then deteriorate with age (mortality rates rise). We present a candidate for such a theory of life history, applied initially to a species with determinate growth. The model features both the quantity and the quality of somatic capital, where it is optimal to initially build up quantity, but to allow quality to deteriorate. The main theoretical result of the paper is that a life history where mortality decreases early in life and then increases late in life is evolutionarily optimal. In order to apply the model to humans, in particular, we include a budget constraint to allow intergenerational transfers. The resultant theory then accounts for all our basic demographic characteristics, including menopause with extended survival after reproduction has ceased.

Subgame perfect equilibrium in continuous games of perfect information: An elementary approach to existence and approximation by discrete games

Abstract This paper relates infinite-action (continuous) games of perfect information to finite-action approximations of such games and thereby obtains a new existence proof for subgame-perfect equilibrium (SPE) in the infinite-action case. Accumulation points of SPE paths of approximating finite-action games are shown to be SPE paths of the limiting infinite-action game. However, no such upper hemi-continuity property holds for SPE strategies. The discontinuity in strategies corresponds to a need for forward induction in the SPE construction for the infinite-action game, thus conflicting with the Harsanyi-Selten principle of subgame-consistency.

The evolution of rationality and the Red Queen

Abstract Strategic rationality is subjected here to natural selection. In a zero-sum repeated game of incomplete information, one long-run individual is informed of the state of the world, and plays against a sequence of short-run opponents who are not. Strategies are noisy and have bounded recall. An equilibrium in these is shown to exist. Relative to any such equilibrium, sufficiently greater recall enjoys an advantage that is not decreasing in the original level of recall, thus capturing the Red Queen effect. The selection pressure to reduce a small amount of noise is less than that to increase recall.