This course covers biological principles at tissue, organ, organismic, and population levels of organization. We will review how animals regulate their internal environment to control or adapt to changes in temperature, salt levels, nutrients, levels of oxygen and carbon dioxide, and the presence of infectious agents. We will examine the molecular, cellular, and tissue mechanisms that underlie the hormonal, neuronal, and behavioral processes that underlie these responses. We will learn how these systems develop in the embryo. At the population level, we will review evidence for evolution, including the tenets of Darwin's theory of evolution by natural selection. We will also discuss the nature and importance of variation among organisms, stochastic processes in evolution, and modern theories of speciation and macroevolution. Finally, the course addresses ecological aspects of population biology, including patterns and processes that inform the distribution and abundance of biodiversity, population growth, organisms' responses to environmental variation, and interactions among species. Each of the topics of the course is explored from a comparative viewpoint to recognize common principles as well as variations among organisms that indicate evolutionary adaptation to different environments and niches.