Aristotle's biology was a combination of scientific observation and philosophical reasoning. He was one of the first to attempt to explain living things in terms of their functions, rather than just describing their physical characteristics. He believed that all living things had a purpose, and that each species was designed for a specific role in the natural world. He also believed that the environment shaped organisms, and that organisms could adapt over time. Aristotle's work laid the foundation for modern evolutionary theory by proposing that species could change over time in response to environmental pressures. His theories on animal behavior were also influential, as he proposed that animals acted out of instinct rather than reason.