A theory for the evolution of behavioral interactions among relatives is developed that allows for genetic correlations between the types of behavior that are expressed in different social contexts. Both theoretical and empirical considerations indicate that such genetic constraints will almost certainly be common in natural populations. It is shown that when genetic correlations between elements of social behavior exist, Hamilton's rule inaccurately describes the conditions for evolution by way of kin selection. The direction in which social organization evolves is a delicate function of the genetic covariance structure among behaviors expressed as an offspring, sibling, parent, etc. A change in this covariance structure caused by random genetic drift or by a change in environment for a population exhibiting genotype-environment interaction can cause the population to suddenly cross a threshold into a new selective domain. Consequently, radical changes in social organization may arise between closely related species without any major shift in selective pressures external to the population.