We study general principles of how living things work in biochemistry and genetics. To find out more about specific organisms we investigate their anatomy, physiology, behavior and ontogeny. To find out how organisms relate we investigate their ecology. At the microscopic level, we study their cell biology.
One of the central concepts in biology is the principle of evolution. The evolutionary history of an organism, i.e. the sequence of ancestral species, is called its phylogeny; it is studied using methods of molecular biology by comparing sequences of genes and proteins, and by investigating ancient forms of life in paleontology. Various methodologies have developed, including phylogenetics, phenetics, and cladistics. An evolutionary timeline outlining the major events in the evolution of life on Earth is available.
The classification of living things is called taxonomy, and should reflect the evolutionary trees of the different creatures. The dominant system is called Linnaean taxonomy. Typically living things were divided into five kingdoms:
However, this five kingdom system is now considered by many to be outdated and the data better reflected by a model starting with the three domains of biological cells:
The distinction between life and non-life never being a hard and fast one, there are also a series of parasites that are progressively less alive:
Major Branches of Biology
People and History
What are our priorities for writing in this area? To help develop a list of the most basic topics in Biology, please see Biology basic topics.