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The development of phenotypic plasticity: where biology and psychology meet.

‘‘The mechanisms that underlie much of behavioral evolution may reside in the processes studied by developmental psychobiologists . . . ’’ Michel & Moore, 1995, p. 178. The counterpart in biology of developmental psychobiology is phenotypic plasticity, or the process by which the internal milieu and the environment induce different phenotypes from a given genotype (Sarkar, 1999; Sarkar & Fuller, 2003). After the rediscovery of Mendel’s work in the early 1900s, some of the first geneticists were occupied with the problem of how animals and plants that reproduced by cloning or were of fixed genotypes could develop very different morphologies in different environments. As genetics developed, however, this question dropped to the wayside in the United States despite the best efforts of T. Dobzhansky and his student, Richard C. Lewontin (2000). Recently, phenotypic plasticity has been rediscovered in a variety of biological disciplines, from molecular genetics to evolutionary biology. But in developmental psychobiology, there has long been an interest in how behavior emerges (Gottlieb, 1992), and the approaches and concepts of this rich field have much to contribute to this newly emerging field in the biological sciences. Much of my work has addressed fundamental precepts in behavioral neuroendocrinology, focusing in particular on the evolution of reproductive behaviors and the neural mechanisms that control them (Crews, 2002). To this end, I have capitalized on experiments of nature, or naturally occurring species. But as a student of Danny Lehrman and Jay Rosenblatt at the Institute of Animal Behavior, I was familiar with the principles of developmental psychobiology, and the last decade has found me coming full circle back to these roots, largely for the reasons captured in the quote of George Michel and Celia Moore (1995) at the beginning of this article. It is in the arena of sex and sexuality that the biological concepts of phenotypic plasticity and the psychobiological principles of development come together. To illustrate this, I will begin by considering the distinction between sex and sexuality and how the study of the former informs, but does not explain, the latter. In so doing, I will describe an animal model system my laboratory has studied for the last decade, one that obviates some of the problems that are inherent in conventional animal models. This work focuses on what constitutes experience and how it influences the development of adult sexuality. Here, I consider the temporal nature and source of experience and how this might affect brain areas that are involved in the display of aggressive and sexual behaviors. I also will present some data on how changes in the brain can constrain future behavior before ending with some comments about transgenerational effects.