ABSTRACT
Evolutionary biologists typically employ a number of major hypotheses for the study of all traits. Perhaps the most important question is whether a given trait has evolved by natural selection and adapts the organism to its environment. If so, then more specific hypotheses are needed to identifY the particular selective forces. For example, a social behavior can evolve by either within-group selection (increasing the fitness of the individual relative to others in its same group) or by between-group selection (increasing the fitness of the group relative to other groups in the total population). Ifthe trait is not a product of natural selection, then another set of specific hypotheses is needed to explain its existence. Perhaps it is an ances-
tral trait that does not vary within the lineage. Perhaps it was adaptive in past environments but failed to keep pace with environmental change. Perhaps it is a costly by-product of another trait that is a product of natural selection, and so on.
