Kin and individual recognition in insects

Insects in a colony have to be able to recognise their relatives and distinguish between close and distant relatives and strangers. Social insects possess highly sophisticated systems of kin recognition, using pheromones acquired from glandular secretions applied to the body or from the nest itself. Strangers may also be recognized by their morphology and social insects are often very sensitive to the texture and shape of any possible intruder. However, it is not necessary to suppose that insects have the concepts of "kin" and "stranger", if they have a chemical information-processing system that effectively discriminates along the lines of these concepts. The abilities of these insects can be explained using a goal-centred intentional stance: all they require is information (pheromonal cues) to allow them to attain their biological goal (exclusion of insects that pose a threat - i.e. non-nestmates). It is not necessary to suppose that insects actually formulate this goal in their minds; they simply behave in a way that realises it. Kin recognition in ants is discussed in the Appendix.

Insects are commonly thought to be unable to recognise other individuals. However, there is new evidence that at least one species of insect - the paper wasp Polistes fuscatus - can do so. Paper wasps use chemical cues to distinguish between friends and intruders. However, they also have distinctive yellow markings on their faces and abdomens. The wasps live within a rigid hierarchy where every individual has a pecking order, suggesting that colony members can tell one wasp from another. Elizabeth Tibbetts, a doctoral candidate and behavioral ecologist at Cornell University, speculated that wasps used visual cues to identify an individual's rank, because of the variety of markings on their faces and bodies. But after studying the variations in color and marking patterns, such as stripe positions and stripe thickness, she could find no apparent correlations between the wasps' markings and their health or social rank (Indiana University, 2003).

Tibbetts explored her hypothesis by inducing changes in wasps' behaviour towards their nestmates by painting the faces and abdomens of some individuals, so as to alter their markings. The altered individuals were the target of hostile attacks for up to two hours, but were eventually accepted on the basis of their chemical cues which identified them as kin (Friedlander, 2002; Abrams, 2003; see Appendix). Had they been taken for outsiders, they would have been attacked much more aggressively. Tibbetts proposes that wasps have two separate identification systems: a chemical system which determines whether a wasp belongs or not, and visual cues to decide the individual identity and rank of wasps whose smell marks them as kin.

"Basically the wasp sees a painted wasp with altered markings and thinks, 'She smells right, so she must be a nest mate, but if I don't recognize her, is she a threat to my rank?' So the wasp is aggressive," said Tibbetts. "Whenever the nest mate then sees the altered wasp, she will know who it is and think, 'No need to worry, it is just Susie over there laying an egg.' Hence individual recognition" (Friedlander, 2002).

Animal behaviourist George Gamboa has suggested a more rigorous way of testing Tibbetts' ideas: if she is right, then a low-ranking wasp, painted to look like a queen, should command queenlike treatment from its nest mates. Unfortunately, Tibbetts does not think she has sufficient artistic skill to carry out such an experiment: "It's one thing to paint a wasp to look unfamiliar, but quite another to paint a wasp so it looks like another wasp" (Choi, 2001).

The ability of wasps to recognise one another is certainly impressive, but does it require a mentalistic explanation? A simpler explanation might be that wasps have an innate tendency to form hierarchical societies and use olfactory and/or visual criteria to distinguish their superiors from their inferiors, by associating higher ranked individuals with their markings. This account could explain how wasps "know" their place. It could also explain wasps' ability to adjust to changes in the hierarchy - when a superior becomes an inferior - if information about the changes is mediated by chemical cues (e.g. if the victor in a struggle for dominance of a colony undergoes chemical changes that convey acccurate information about its newly achieved reproductive status and inhibit aggression from other individuals). Changes in the hierarchy could also be explained by chemical cues signalling a decline in an individual's reproductive fitness (leading to challenges by subordinates), as well as uncontrolled external factors. Certain ants appear to use such a system (Monnin and Peeters, 1999). However, the dominance criteria employed by paper wasps are more complicated (Seppa, Queller and Strassman, 2002). Additionally, as we saw above, there is no correlation between a wasp's visual markings and its rank.

This non-mentalistic account has one additional limitation: it presupposes that there is a well-ordered set of criteria for deciding an individual's current rank, enabling each member to distinguish its superiors from its inferiors. The fact that Tebbitts managed to upset the hierarchy in her experiment suggests the contrary. The hostility shown towards painted individuals (aggression took two hours to die down) is suggestive of something akin to cognitive dissonance: the wasps were confused.

On the other hand, if wasps actually have a mental concept of an "individual", how do they conceive of an individual? Do they conceive of an individual as an embodied being ("Joe") that persists over time despite changes, or simply as a place-holder - i.e. whatever it is that occupies a certain position in the social hierarchy ("rank two")? And how do they acquire their concept of an individual? Is it hard-wired, or acquired through experience? Do wasps really wonder who their nestmates are when they return to the colony with altered markings, and speculate about their rank, as Tibbetts supposes?

Another potential indicator of conceptual awareness in wasps would be evidence that wasps can make transitive inferences (e.g. if a wasp knows that A dominates B, and B dominates C, then it should realise that A dominates C, even though it has never seen A and C together). As far as I know this ability has not been tested in wasps. Such an ability would suggest that wasps have an internal mental representation of the other individuals in their colony. On the other hand, there are sophisticated associationist, "non-cognitive" models which support transitive inferences within small groups. It appears likely that both mechanisms occur in nature. Cognitive mechanisms are more likely to underlie the behaviour of social animals in the wild, which live in much larger groups and whose dominance hierarchies have to be rapidly learned (Allen, 2004).

The upshot of the foregoing discussion is that an animal's ability to recognise other individuals is not a definitive indicator of the presence of mental states.

The discussion raises a deeper philosophical question. If animals' minds are anything like ours, at least some of their concepts are innate. How can we identify these concepts, and how do we distinguish from from (non-mentalistic) hard-wired behavioural patterns?