Genes, Environments, and Time: The Biology of Adversity and Resilience Thomas Boyce, MD,a Pat Levitt, PhD,b,c Fernando D. Martinez, MD,d Bruce S. McEwen, PhD,e,† Jack P. Shonkoff, MDf,k,j,g,h,i Exposures to adverse environments, both psychosocial and physicochemical, are prevalent and consequential across a broad range of childhood populations. Such adversity, especially early in life, conveys measurable risk to learning and behavior and to the foundations of both mental and physical health.