Friday, June 27, 2014

Stephen C. Stearns - Economic Decisions for the Foraging Individual

Here's another useful video lecture. It's from the Open Yale Course 'EB122: Principles of Ecology, Evolution and Behavior', taught by Stephen C. Stearns, Edward P. Bass Professor of Ecology and Evolutionary Biology.

Here is his overview of the lecture:
There are several ways to examine the behaviors of organisms when they forage or hunt for food or mates. These behaviors become more complex in higher organisms, such as primates and whales, which can hunt in groups. Foragers and hunters have been shown to examine the marginal cost and marginal benefit of continuing an action and then adjust their behaviors accordingly. They are also able to handle risk by hoarding resources.
Here is the course home page on Yale Open Courses.

This material is of interest because of the importance of economic analyses of decisions by living animals, and foraging is an area where there's been considerable progress. Behavioural ecology is one of the areas in science where you'll regularly run into talk of common currencies. Behavioural ecologists are sometimes relatively agnostic about the mechanisms producing behaviour, but sometimes intensely interested in them. (The same course includes a useful session - number 10 - on genomic conflict.)

Tuesday, June 24, 2014

Ultimate currencies can be subjective or evolutionary

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.

Related postings:


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.

Monday, June 23, 2014

The Google Scholar ‘Common Currency Ratio’

I’m a big fan of Google Scholar (and Google Scholar Citations). I use them both regularly to identify academic literature on a wide range of topics, and to trace, at least in outline, the responses to specific papers. I was fiddling about with it the other day, and wondered whether I could use it to try to develop a measure, even if a rough one, of the extent to which reference to common currencies occurs in a person’s published research.

My first attempt is the following:

  • An author’s Common Currency Score (CCS) is the number of results on Google Scholar for the author’s name (in quotation marks), plus “common currency” (also in quotation marks).
  • An author’s Common Currency Ratio (CCR) is their CCS divided by the number of results for their name alone.

This is rougher than a warthog’s shins, and will be hugely unsatisfactory in cases of names corresponding to multiple authors. (It’s pretty bad for authors whose names are indexed in more than one way - for example “PW Glimcher” returns about 3 times as many correct results as “PW Glimcher”. But searching for “DJ McFarland” picks up irrelevant McFarlands including false positives.)

Rough and ready though this is, it isn’t devoid of interest. George Ainslie has the highest CCS and CCR of anyone I thought to search for. I might update this in the future - as I apply it to other authors, or refine it in some way or other.

George Ainslie (22 June):
Common Currency Score (CCS) = 117
“George Ainslie” = 1680
George Ainslie CCR: 0.07

John McNamara (23 June)
Common Currency Score (CCS) = 151
“JM McNamara” = 3560
John McNamara CCR = 0.04

Paul Glimcher (22 June)
Common Currency Score (CCS) = 92
“PW Glimcher” = 1510
CCR: 0.06

David McFarland (22 June)
Common Currency Score (CCS) = 61 (for “DJ McFarland”)
“David McFarland” = 1130
David McFarland CCR = 0.05

David Spurrett (22 June)
Common Currency Score (CCS) = 25
“David Spurrett” = 455
David Spurrett CCR = 0.05

Peter Shizgal (23 June)
Common Currency Score (CCS) = 36
“P Shizgal” = 1070
Peter Shizgal CCR = 0.03

Michel Cabanac (23 June)
Common Currency Score (CCS) = 109
“M Cabanac” = 2320
Michel Cabanac CCR = 0.04