Biology is the natural science that involves the study of life and living organisms, including their physical structure, chemical composition, function, development and evolution. Modern biology is a vast field, composed of many branches. Despite the broad scope and the complexity of the science, there are certain unifying concepts that consolidate it into a single, coherent field. Biology recognizes the cell as the basic unit of life, genes as the basic unit of heredity, and evolution as the engine that propels the creation of new species. Living organisms are open systems that survive by transforming energy and decreasing their local entropy to maintain a stable and vital condition defined as homeostasis. See glossary of biology.
When you study science, and especially these realms of the biology of what makes us human, what's clear is that every time you find out something, that brings up ten new questions, and half of those are better questions than you started with.
Robert Sapolsky (2003) Emperor Has No Clothes Award acceptance speech