All sciences ultimately study nature.
Our world contains over 1.25 million distinct species of life ranging in size from microscopic bacteria to a fungus in Crystal Falls, Michigan estimated to weigh 100 tons. Between these extremes exists a very diverse range of living beings. His system, with some modification, is still in use today. The changes in classification over time are best illustrated through the plant kingdom. Then the work of Charles Darwin on the evolution of species implied that there must have been more than two kingdoms.