The theory of evolution is classified within the Biological kingdom. Evolutionary biology studies the processes that have led to the diversity of life on Earth, proposing that all species share a common ancestor and have evolved over time through mechanisms like natural selection and genetic drift. This theory underpins much of modern biological science, providing a framework for understanding the relationships among species and the adaptation of organisms to their environments. By classifying species according to evolutionary relationships, biologists can better understand the history of life and the complex interactions that shape ecosystems and biodiversity.