Scientific Understanding of Consciousness
Face Recognition in Distant Taxa
Science 2 December 2011: Vol. 334 no. 6060 pp. 1272-1275
Michael J. Sheehan, Elizabeth A. Tibbetts
Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109, USA.
We demonstrate that the evolution of facial recognition in wasps is associated with specialized face-learning abilities. Polistes fuscatus can differentiate among normal wasp face images more rapidly and accurately than nonface images or manipulated faces. A close relative lacking facial recognition, Polistes metricus, however, lacks specialized face learning. Similar specializations for face learning are found in primates and other mammals, although P. fuscatus represents an independent evolution of specialization. Convergence toward face specialization in distant taxa as well as divergence among closely related taxa with different recognition behavior suggests that specialized cognition is surprisingly labile and may be adaptively shaped by species-specific selective pressures such as face recognition.
The cognitive mechanisms underlying learning abilities are surprisingly similar across taxa as diverse as mammals, birds, insects, and mollusks. Although the mechanisms that underlie learning are broadly generalized across animals, there is increasing evidence that learning abilities are adaptively shaped by species’ ecology and can be highly specialized. One of the most striking examples of specialized cognition is specialized face learning found in some mammals, including humans. Individual face recognition is an important aspect of human social interactions, and our brains process the images of normal conspecific faces differently than any other images. Further, individual recognition is a type of complex social behavior that could favor specialized cognition because it requires flexible learning and memory and has the potential to dramatically increase cognitive demands. However, the claim that face specialization is an adaptation to facilitate individual recognition has been contentious, in part because it is unclear whether face learning is based on conserved mechanisms or has evolved independently in multiple mammalian lineages. If face specialization is an adaptation to facilitate face recognition, we predict that specialization will be associated with the evolution of facial individual recognition across distant taxa.
Paper wasps are a good system for examining the evolution of face specialization because closely related wasp species differ in their ability to individually recognize conspecific faces. The paper wasp, Polistes fuscatus, has variable facial features that are used to recognize individual conspecifics. Visual recognition is possible in Polistes wasps because they have acute vision and live in well-lit nests. P. fuscatus nests are often initiated by groups of cooperating queens, in which relative reproduction is determined by a strict linear dominance hierarchy; individual recognition stabilizes social interactions and reduces aggression within these cooperative groups. Some wasp species, such as Polistes metricus, typically nest alone and therefore lack competition among queens. Solitary nest founding is associated with a lack of facial pattern variability, and experiments have shown that P. metricus does not recognize conspecifics as individuals
Overall, our data suggest that selection for efficient individual recognition has led to the adaptive evolution of specialized face learning in the paper wasp P. fuscatus. Specialized face learning provides a remarkable example of convergent evolution between wasps and mammals. Although mammals and wasps have dramatically different eyes and neural structures, specializations for recognizing conspecific faces have arisen independently in both groups. Although specialized face learning in mammals and wasps are phenomenologically similar, they are likely to have different mechanistic bases. Face learning in primates and sheep is highly specialized, involving multiple brain regions and face-specific neurons. Examining whether similar neural signatures of cognitive specialization are found in the “miniature” brain of an insect provides an interesting avenue for future comparisons. The evolutionary flexibility of specialized face learning is striking and suggests that specialized cognition may be a widespread adaptation to facilitate complex behavioral tasks, such as individual recognition.
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