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Most ant colonies have a single queen, who settles into a life of fecund bliss after a single mating flight in which she left her home nest, mated, and then spurned any further gallivanting by chewing her own wings off and digging a chamber for her eggs underground. But in a tropical ant species called Pachycondyla villosa, which lives in forests from southern Texas to Argentina, several of the young queens (older literature actually refers to them as princesses, though this terminology is not seen much any more) band together to make a nest in a bit of rotting wood and form a society with a dominance hierarchy and division of labor among the members. As with the wasps, it stands to reason that sorting out whose turn it is to take out the trash would be easier if the ants could tell each other apart. D'Ettorre tested this idea by collecting some of these new queens in Brazil and allowing pairs of them to establish a dominance relationship in the lab. The ants fight by biting, stinging, and boxing with their antennae until one party backs off. Then each queen was allowed to interact with either her former companion or an unfamiliar female. In some trials, D'Ettorre anesthetized the ant her subjects were given to ensure that it was really an individual odor cue, and not just generally aggressive or submissive behavior, that could be used to distinguish one ant from another. In all cases, both the dominant and subordinate queens recognized their former partners. Chemical analysis of the ants' exoskeletons showed no relationship between any particular compound and whether a queen was dominant or subordinate, confirming that the ants were not simply reacting to a generalized "alpha ant" smell. What was even more astonishing was the ants' memory: even after 24 hours of separation, a hefty interval for an animal that lives just a few weeks or months, the queens remembered their previous encounters and behaved accordingly when the two females met (whether there was any frantic internal searching for identity, a kind of ant version of "You smell so familiar but I just can't remember who won when we were together," wasn't discussed).

Finally, what does being able to distinguish a tiny blob of black or yellow, and remember who has which variant, mean about the brain of the insects that exhibit such a sophisticated ability? In many animals, the part of the brain controlling a much-used behavior is comparatively larger than in species that seem to need it less; thus, for example, bats and owls have disproportionately large portions of their brain devoted to hearing. Neurobiologists Wulfia Gronenberg and Lesley Ash checked out Tibbetts's wasps, as well as other closely related species, and found that being able to recognize faces didn't mean having a larger brain or larger visual centers. Interestingly, the wasps with the recognition abilities had smaller olfactory centers. Another part of the brain with the rather peculiar name of mushroom body was larger than expected, but the difference was quantitative rather than qualitative, suggesting that such a capability is nothing that unusual among wasps, and that similar abilities may be discovered if we simply look for them.

Personalities and Evolution

ALTHOUGH individual variation in animal personalities is a somewhat novel idea for biologists, variation itself is not, being the stuff that underlies evolution. Natural selection acts by some variants reproducing better than others, leading to a preponderance of the fitter genes in the population. But this seems like a paradox in the consideration of personality as consistent differences in behavior: if individuals are different, don't some of them perform better than others? And if so, why haven't the more successful ones come to outnumber the less successful ones, so that we are left with only those personality types that are optimal for their environment?

This question is part of a much larger one, namely, what maintains all the tremendous