Individuals in a population vary in heritable characteristics: organisms produce more offspring than the environment can support. Individuals that are well suited to their environment tend to leave more offspring than other individuals: over time, favorable traits accumulate in the population. Data that documents the pattern of evolution: direct observation. Ex: natural selection in response to introduced plant species; evolution of drug-resistant bacteria: homology. Ex: human arm vs cat leg vs whale fin vs bat wing. Not to be confused with convergent evolution. The evolution of similar, analogous features in distantly related groups. Ex: sugar glider vs flying squirrel: the fossil record. Provides evidence of the extinction, origin, and changes within species over time: biogeography. The study of the geographic distribution of species. Endemic species are not found anywhere else in the world. Individuals with certain heritable traits survive and reproduce at a higher rate than other individuals. Ns increased the match between organisms and their environment over time.