Biology concerns itself primarily with understanding the life-mechanisms, diversity, relatedness and adaptedness of life forms, and the processes shaping the spatial and temporal patterns we see in the living world. Evolution, broadly taken, explains the diversity, relatedness and adaptedness of life forms. In this talk, I will develop a view of biology that stresses the dynamics of how population compositions change over time, emphasizing the interplay of three major “phenomena” in biology: development, ecology and heredity. The picture emerging from this view of biology constitutes the framework within which much of the mathematical modeling in both ecology and evolutionary biology is carried out. I will discuss this framework in an attempt to clarify the relationships between the various approaches to modeling the evolutionary process that are taken in evolutionary ecology, population genetics and quantitative genetics.