Bruce J. Ellis, PhD, spent the early years of his career at the University of Canterbury in New Zealand before taking up his current position as an Associate Professor of Family Studies and Human Development at the University of Arizona. He completed his doctoral work in evolutionary psychology at the University of Michigan and his postdoctoral work in the National Institute of Mental Health's Developmental Psychopathology Training Program at Vanderbilt University. The major focus of his research is on testing conditional adaptation models of the effects of early family environments on the timing of pubertal development and first sexual and reproductive activity. Dr. Ellis received the 1999 John F. Kennedy Center Young Scientist Award and has served on the editorial boards of Developmental Psychology, Evolutionary Psychology, Personality and Social Psychology Review, and Personal Relationships.

David F. Bjorklund, PhD, is Professor of Psychology at Florida Atlantic University, where he has taught graduate and undergraduate courses in developmental psychology since 1976. His research has focused primarily on children's cognitive development, particularly memory and strategy development. More recent interests include the adaptive nature of immaturity, deferred imitation in juvenile great apes, and evolutionary developmental psychology. Dr. Bjorklund is the author of several books, including The Origins of Human Nature: Evolutionary Developmental Psychology (with Anthony D. Pellegrini). He is a former Associate Editor of Child Development and has served on the editorial boards of the Journal of Experimental Child Psychology, Journal of Cognition and Development, Developmental Review, Educational Psychology Review, Journal of Comparative Psychology, Developmental Psychology, Cognitive Development, and School Psychology Quarterly.

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