How do we, as individuals, become who we are? How our bodies function, our minds perceive the world, and we behaviorally respond to the challenges we face are shaped by early life experiences. Recent research by evolutionary anthropologists, biopsychologists, nutritionists, and behavioral neuroscientists has demonstrated that a developmental, evolutionary perspective substantially informs our understanding of the phenomena of individual differences. This symposium discusses mechanisms and pathways through which early life environment exert profound influences on humans and non-human primates and considers the potential functions of this developmental plasticity regulating life-history trade-offs. In this symposium, speakers will juxtapose the behavioral care of mothers, fathers, and wider social networks with physiological investment of the placenta and mother’s milk. Moreover, epigenetic modification can result from the interaction between the infant’s genome and the behavioral and physiological environments of early life and previous generations. This symposium will provide exposure to a wide range of methodological and theoretical approaches to developmental trajectories and model how researchers might productively integrate these different perspectives into their own work.