Recent advances in molecular genetics and epigenetics are reviewed that have major implications for the bio-behavioral sciences and for understanding how organisms adapt to their environments at both phylogenetic and ontogenic levels. From a post-genomics perspective, the environment is as crucial as the DNA sequence for constructing the phenotype, and as a source of information in trying to predict phenotypes. The review is organized with respect to four basic processes by which phenotypes adapt to environmental challenges, with an emphasis on the data for humans: (1) developmental plasticity, (2) epigenetic mechanisms, (3) genotype-environment correlations, and (4) gene x environment interactions.