Developmental Biology has been revolutionized by the flood of methods and insights from molecular biology and genetics, as well as experienced a resurgence of interest in developmental pathways and fields. Developmental biology is the science that investigates how a variety of interacting processes generate an organism's heterogeneous shapes, size, and structural features that arise on the trajectory from embryo to adult or, more generally, through a life cycle. It represents a good area of contemporary experimental biology that focuses on phenomena that have puzzled natural philosophers and scientists for more than two millennia. Philosophers of biology have shown interest in developmental biology due to the potential relevance of development for understanding evolution, the theme of reductionism in genetic explanations and increased attention to the details of particular research programs, such as stem cell biology.