Wilfred Trotter's research on the herd instinct incorporates two major elements: psychoanalytic theory and an early interest in biosociology. Trotter was among the first to apply cross-species comparisons in the social sciences, and his contributions in this area are reviewed and evaluated in the light of more recent work in the biosocial bases of human behavior. Trotter's work is considered an important, if neglected, episode in the laying of a conceptual foundation for biosocial paradigms which, it is argued, do not preclude designs for melioristic planning.