Recognition of conspecifics occurs when individuals classify sets of conspecifics based
on sensory input from them and associate these sets of input with different responses.
Classification of conspecifics can vary in specificity (the number of individuals
included in a set) and multiplicity (the number of sets differentiated). In other words,
the information transmitted varies in complexity. Although recognition of conspecifics
has been reported in a wide variety of organisms, few of these reports have addressed the
specificity or multiplicity of this capability.
This review provides discusses examples of these patterns, the mechanisms that can
produce them, and the evolution of of these mechanisms. Individual recognition is one end
of a spectrum of specificity, and binary classification of conspecifics is one end of a
spectrum of multiplicity. In some cases, recognition requires no more than simple forms
of learning, such as habituation, yet results in individually specific recognition. In
other cases, recognition of
individuals involves complex associations of multiple cues
with multiple previous experiences in particular contexts.
Complex mechanisms for recognition are expected to evolve only when simpler mechanisms do
not provide sufficient specificity and multiplicity to obtain the available advantages.
In particular, the evolution of cooperation and deception is always promoted by
specificity and multiplicity in recognition. Nevertheless, there is only one
demonstration that recognition of specific individuals contributes to cooperation in
animals other than primates.
Human capacities for individual recognition probably have a central role in the evolution
of complex forms of human cooperation and deception. Although relatively little studied,
this capability probably rivals cognitive abilities for language.