Ultimate currencies can be evolutionary or subjective
Claims about common currencies are offered as explanations of one or both of two putative facts:
- The currency represents the fundamental principle in some pattern in the choices made by some agent. These are ultimate currencies. OR
- The currency is a psychologically real characteristic of the processes by which choice is produced. These are proximal currencies.
Any single ranking of options on a scale such that the behaviour of an agent can be described as – perhaps approximately – consistent with that ordering counts as an ‘ultimate’ common currency. An ultimate currency relates values to options, or to what selecting those options achieves or perhaps have the function of achieving. It is easy to imagine possible instantiations of an ultimate currency (‘all of Jim’s actions are efficiently ordered to contribute to the greater glory of the Flying Spaghetti Monster’) but among the scientifically interesting forms of consistency, two families stand out. One of these relate to fitness, and the other to some of other form of utility.
Here’s Don Ross describing Paul Samuelson’s work on what came to be called revealed preference theory:
“Paul Samuelson (1938) […] set out to define utility in such a way that it becomes a purely technical concept. Since Samuelson's re-definition became standard in the 1950s, when we say that an agent acts so as to maximize her utility, we mean by ‘utility’ simply whatever it is that the agent's behavior suggests her to consistently act so as to make more probable.” (Ross, 2005)
It would be difficult to find a clearer statement of the basic idea of an ultimate common currency. As I said, the two main scientifically interesting variants of claims about ultimate currencies relate to fitness, or to utility.
I therefore say that an ultimate currency can be evolutionary or subjective. Here I’m knowingly, albeit slightly, departing from standard usage, insofar as the usual way of distinguishing proximal from ultimate has the latter taken to be synonymous with fitness promoting. (The standard sense is partly preserved here, because the values in an evolutionary ultimate currency are a function of contribution to fitness.) A guiding presumption of behavioural ecology is that behavioural dispositions make contributions to fitness, and that to the extent that the dispositions have a heritable basis, selection will tend to drive them towards making (constrained) optimal contributions. The following statement by McNamara and Houston is an exemplary (and frequently quoted) assertion about an evolutionary ultimate currency:
“Any attempt to understand behavior in terms of the evolutionary advantage that it might confer has to find a "common currency" for comparing the costs and benefits of various alternative courses of action” (McNamara and Houston 1986: 358).
There are compelling reasons for thinking that natural selection will operate on at least some behavioural tendencies, and so a strong general justification for the project of behavioural ecology. Nonetheless, the question of whether the behaviour allocation of the individuals in any particular species does indeed tend to optimise fitness (or would have in historical selective environments) is an empirical one. Behavioural ecologists have studied many species and types of behaviour and achieved striking successes in restricted domains such as foraging and mate selection. These successes have often relied on focusing on a simplified and more empirically tractable currency such as net rate of calorie intake (in the case of foraging), or the health of the selected mate (in mate selection). These proxy currencies plausibly contribute to fitness. Even so, success relating behaviour patterns to the proxies falls short of establishing relationships between all behavioural dispositions and overall fitness in any species. Two of the most serious shortfalls are in the area of relative allocation between significantly different modalities (such as calorie intake versus pursuit of mating opportunities versus predator avoidance) and variation in allocation over extended periods of time, including the full life-history.
(I note as an aside here that evolutionary psychologists tend to share the general theoretical orientation of behavioural ecologists, but not to make claims about common currencies. I’m not sure why this is. Perhaps they’re mostly more interested in attempting to establish the existence of biases or preferences that fit with their theoretical orientation, and being interested in their relative strengths is the sort of thing that comes later. Those evolutionary psychologists who are most committed to modularity and opposed to central systems, though, seem to be committed - if only by implication - to denying the possibility of a proximal common currency.)
Anyway, enough about ultimate common currencies.
A subjective ultimate currency, in contrast, attributes values that are a function of the revealed preferences or inferred utilities of the individual agent, without requiring any relationship to fitness. Ross’s description of Samuelson, quoted above, states the key idea. The paradigmatic sciences of subjective ultimate currencies are microeconomics (with variously regimented notions of utility functions revealed through consumption) and behavioural psychology (where strength of reinforcement is defined in terms of effect on patterns of behaviour allocation). Evolutionary ultimate currencies, then, have stronger empirical conditions than subjective ones, because the latter require ‘mere’ consistency in behaviour, whereas the former require consistency in contributing to fitness.
The distinction between evolutionary and subjective ultimate currencies, as I’ve sketched it here, conceals considerable technical detail. There are different and competing fitness concepts, debates over the level (especially gene or individual) at which selection operates, and differing positions over the correct (if any) individuation principles for genes, genomes, species and other relevant categories. There are also competing utility concepts, offering different explanations of the same empirical data.
McNamara, J.M. and Houston, A.I. (1986) The Common Currency for Behavioral Decisions, The American Naturalist, 127(3), pp358-378.
Ross, D. (2005). Economic Theory and Cognitive Science, Volume One: Microexplanation. Cambridge, MA: MIT Press.