John M. C. Hutchinson

Simple heuristics and rules of thumb: Where psychologists and behavioural biologists might meet

The Centre for Adaptive Behaviour and Cognition (ABC) has hypothesised that much human decision-making can be described by simple algorithmic process models (heuristics). This paper explains this approach and relates it to research in biology on rules of thumb, which we also review. As an example of a simple heuristic, consider the lexicographic strategy of Take The Best for choosing between two alternatives: cues are searched in turn until one discriminates, then search stops and all other cues are ignored. Heuristics consist of building blocks, and building blocks exploit evolved or learned abilities such as recognition memory; it is the complexity of these abilities that allows the heuristics to be simple. Simple heuristics have an advantage in making decisions fast and with little information, and in avoiding overfitting. Furthermore, humans are observed to use simple heuristics. Simulations show that the statistical structures of different environments affect which heuristics perform better, a relationship referred to as ecological rationality. We contrast ecological rationality with the stronger claim of adaptation. Rules of thumb from biology provide clearer examples of adaptation because animals can be studied in the environments in which they evolved. The range of examples is also much more diverse. To investigate them, biologists have sometimes used similar simulation techniques to ABC, but many examples depend on empirically driven approaches. ABCs theoretical framework can be useful in connecting some of these examples, particularly the scattered literature on how information from different cues is integrated. Optimality modelling is usually used to explain less detailed aspects of behaviour but might more often be redirected to investigate rules of thumb.

Use, misuse and extensions of "ideal gas" models of animal encounter

Biologists have repeatedly rediscovered classical models from physics predicting collision rates in an ideal gas. These models, and their two‐dimensional analogues, have been used to predict rates and durations of encounters among animals or social groups that move randomly and independently, given population density, velocity, and distance at which an encounter occurs. They have helped to separate cases of mixed‐species association based on behavioural attraction from those that simply reflect high population densities, and to detect cases of attraction or avoidance among conspecifics. They have been used to estimate the impact of population density, speeds of movement and size on rates of encounter between members of the opposite sex, between gametes, between predators and prey, and between observers and the individuals that they are counting. One limitation of published models has been that they predict rates of encounter, but give no means of determining whether observations differ significantly from predictions. Another uncertainty is the robustness of the predictions when animal movements deviate from the model’s assumptions in specific, biologically relevant ways. Here, we review applications of the ideal gas model, derive extensions of the model to cover some more realistic movement patterns, correct several errors that have arisen in the literature, and show how to generate confidence limits for expected rates of encounter among independently moving individuals. We illustrate these results using data from mangabey monkeys originally used along with the ideal gas model to argue that groups avoid each other. Although agent‐based simulations provide a more flexible alternative approach, the ideal gas model remains both a valuable null model and a useful, less onerous, approximation to biological reality.

Is more choice always desirable? Evidence and arguments from leks, food selection, and environmental enrichment

Recent studies on humans show that too much choice can make subjects less likely to choose any item. I consider general adaptive and non‐adaptive explanations of why such choice aversion, or its converse, might occur in animals. There are three questions: is more choice always preferred, does it ever lead to less consumption (or a lower probability of consumption), and may it result in worse items being selected? A preference for choice is one of the main explanations for lek formation and I draw attention to previously unrecognised parallels with models of human shopping behaviour. There is indeed evidence of female preference for larger leks, although much of the observational data are open to other interpretations. Unfortunately nobody has looked for choice aversion where it is most to be expected, in leks larger than normally occur. Evidence that too much choice of males confuses females is strongest in acoustically advertising frogs, but the widespread decrease of mating skew in larger leks might also have this explanation. A model reanalyses data on skew in black grouse Tetrao tetrix and suggests that considering only a random subset of a large lek may increase the chances of selecting the better males: larger leks are more likely to include better males, but these are less likely to be selected. These opposing effects may lead to an optimum lek size, but only with a sufficient decline in choice accuracy with size. With food choice, very few studies have avoided confounding choice with food quality, by manipulating only flavour. The widespread phenomena of stimulus‐specific satiety and novelty seeking imply that monotonous diets are aversive, but no studies test whether animals choose sites where they know food diversity to be greater. Operant experiments that demonstrate mild preferences for free choice concern choice about the means to get food rather than the food itself. In some insect species even moderate choice of diet can be deleterious, and studies on search images and the confusion effect may be evidence of this in vertebrates. Environmental enrichment of captive animals often relies on increasing the options available, but it need not be the choice itself that is beneficial. I consider briefly further areas in biology where choice preference or aversion are potentially important.

Patch leaving in humans: can a generalist adapt its rules to dispersal of items across patches?

We used a computer game to examine three aspects of patch-leaving decisions in humans: how well do humans perform compared to the optimal policy, can they adjust their behaviour adaptively in response to different distributions of prey across patches and on what cues are their decisions based? Subjects earned money by catching fish when they briefly appeared within a pond; the timing of appearances was stochastic but at a rate proportional to how many fish remained. Caught fish were not replaced and ponds varied in how many fish they initially contained (according to three different distributions). At any point subjects could move to a new pond, but travel took some time. They delayed this switch much too long. Furthermore, regardless of the distribution of prey, subjects spent longer at ponds where they had found more items (contrary to optimality predictions in two of the environments). However, they apparently responded not to the number of captures directly (despite this appearing on screen) but to the current interval without a capture, to the interval preceding the last capture, and to the time spent at the current pond. Self-reports supported this order of cue importance. Subjects often left directly after a capture, perhaps an example of the Concorde fallacy. High success rate in the preceding patch decreased residence time and subjects appeared to be learning to leave earlier over the latter two thirds of the experiment. Minimization of delay to the next capture alone might explain some of the suboptimal behaviour observed.

Fishing for the right words: Decision rules for human foraging behavior in internal search tasks

Animals depleting one patch of resources must decide when to leave and switch to a fresh patch. Foraging theory has predicted various decision mechanisms; which is best depends on environmental variation in patch quality. Previously we tested whether these mechanisms underlie human decision making when foraging for external resources; here we test whether humans behave similarly in a cognitive task seeking internally generated solutions. Subjects searched for meaningful words made from random letter sequences, and as their success rate declined, they could opt to switch to a fresh sequence. As in the external foraging context, time since the previous success and the interval preceding it had a major influence on when subjects switched. Subjects also used the commonness of sequence letters as a proximal cue to patch quality that influenced when to switch. Contrary to optimality predictions, switching decisions were independent of whether sequences differed little or widely in quality.

Is Risk Taking Used as a Cue in Mate Choice

More frequent risk taking among young men than women has been explained as a sexually selected trait, perhaps advertising male quality. We investigated this hypothesis in three studies. (1) Young men and women rated how attractive they would find it if a potential partner took various specific risks. A domain-specific risk inventory allowed us to distinguish whether risk taking is attractive generally or only in certain domains. Both sexes reported social and recreational risk taking as attractive (the latter not always significantly so), but other domains of risk taking as unattractive (ethics, gambling, and health) or neutral (investment). The sexes differed markedly little. Parallel studies in Germany and the United States yielded very similar results. (2) We asked subjects to predict how attractive the other sex would find it if the subject performed each risky behavior. Both sexes were rather accurate (which could be merely because they assume that the other sex feels as they do) and sex differences in attractive risk taking are not explicable by sex differences either in attraction or in beliefs about what others find attractive. However, our data could explain why unattractive risks are more often taken by men than women (men slightly underestimated the degree of unattractiveness of such risks, whereas U.S. women overestimated it, perhaps because they themselves found such risk taking more unattractive than did U.S. men). (3) Both members of 25 couples reported their likelihood of engaging in specific risky behaviors, their perception of these risks, and how attractive they would have found these behaviors in their partner. One hypothesis was that, for instance, a woman afraid of heights would be particularly impressed by a man oblivious to such risks. Instead we found positive assortment for risk taking, which might be explained by a greater likelihood of encountering people with similar risk attitudes (e.g. members of the same clubs) or a greater compatibility between such mates. Finally, contrary to the assumption that taking a low risk is likely to be less revealing of an individuals quality than taking a high risk, we found a strong negative relationship between the perceived riskiness of a behavior and how attractive it was judged.

Site fidelity and recurrence of some migrant bird species in The Gambia

Regular ringing was carried out over most of five winters at Ginak in The Gambia. We analyse retrap data from 12 species of migrant birds to examine whether they remain for more than one day within a winter, and whether they return to the study area in subsequent winters. We investigate both the rate of recurrence (between‐winter retraps within the whole area, approximately 1,000m across) and site fidelity (tendency to be retrapped within 100m of first capture). Some adjustment of recurrence for annual survival is attempted. For individuals trapped at least twice over a winter, we tabulate the interval between first and last capture: in all 12 species this was over six weeks for some individuals; furthermore, site fidelity within a winter is demonstrated in most species retrapped in reasonable numbers, exceptions were Garden Warbler Sylvia borin and Blackcap Sylvia atricapilla. Most species recurred at appreciable rates in successive seasons, and in three species with a sufficient sample size, Subalpine Warbler Sylvia cantillans, Whitethroat Sylvia communis, and less certainly Olivaceous Warbler Hippolais pallida, the evidence was of site fidelity between winters. We compare recurrence rates with data collected at Djoudj in north Senegal.

Mating behaviour in the terrestrial slug Deroceras gorgonium : Is extreme morphology associated with extreme behaviour?

Mating in Deroceras consists of an investigation phase (precourtship), then a long courtship involving mutual stroking with the extruded sarcobelum, then sperm exchange (copulation). The penial gland, if present, everts over the partners skin during copulation: this is hypothesised to apply a secretion manipulating the partner to use received sperm. Deroceras gorgonium has a particularly large penial gland divided into many finger-like branches. We studied D. gorgonium mating behaviour in the hope of further indications of the glands function. Precourtship and courtship together last longer than in other Deroceras (ca. 6 h to >9 h); precourtship is highly variable, often with many bouts of different behaviours, including seemingly inactive phases. During most of the courtship partners remain apart waving their particularly long, pointed sarcobela; only at a later stage do the tips of these contact the partner. This waving alternates with circling for half a turn. For the first time in Deroceras we observed the sarcobelum transferring a secretion. The copulation is amongst the fastest: genital eversion and sperm exchange occur within 1 s, and slugs separate 18-25 s later. The penial gland is everted immediately after sperm exchange, but, surprisingly, is often spread underneath the partner rather than over its back and, if on top, is not always fully spread over the partners body. We discuss these observations with respect to penial gland morphology and in the light of possible sexual conflicts. The long courtship and distant sarcobelum waving might reflect attempts to transfer, but not receive, secretion, and the circling might serve for size assessment.

Penis-biting slugs: Wild claims and confusions

We thank Janet Leonard and Thierry Backeljau for comments, and Katrin Schniebs for translation.

Connecting behavioural biologists and psychologists: Clarifying distinctions and suggestions for further work

This article is a reply to the commentaries on our target article, which relates our group’s work on simple heuristics to biological research on rules of thumb. Several commentators contrasted both these approaches with behaviour analysis, in which the patterns of behaviour investigated in the laboratory are claimed to be near-universal attributes, rather than specific to particular appropriate environments. We question this universality. For instance, learning phenomena such Pavlovian or operant conditioning have mostly been studied only in a few generalist species that learn easily; in many natural situations the environment hinders learning as an adaptive strategy. Other supposedly general phenomena such as impulsiveness and matching are outcome models, which several different models of simple cognitive processes might explain. We clarify some confusions about optimisation, optima and optimality modelling. Lastly, we say a little more about how heuristics might be selected, learnt and tuned to suit the current environment.