There are five unifying principles of biology:
Cell theory. All living organisms are made of one or more cells, the basic living unit of function in organisms. All cells come from preexisting cells that multiply through cell division.
Evolution. Through natural selection and genetic drift, a population's inherited traits change from generation to generation.
Genes. A living organism's traits are encoded in DNA. Segments of DNA that, taken as a whole, specify a trait are known as genes. In addition, traits are passed on from one generation to the next by way of these genes. All information transfers from the genotype, the unobservable genetic traits, to the phenotype, the observable physical or biochemical characteristics of the organism. Although the phenotype expressed by the gene may adapt to the environment of the organism, that information is not transferred back to the genes. Only through the process of evolution do genes change in response to the environment.
Homeostasis. The physiological processes that allow an organism to maintain its internal environment notwithstanding its external environment.
Energy. The attribute of any living organism that is essential for its state. (e.g. required for metabolism)
Cell theory states that:
The cell is the fundamental unit of life.
All living things are composed of one or more cells or the secreted products of those cells, such as shells.
Cells arise from other cells through cell division
In multicellular organisms, every cell in the organism's body is produced from a single cell in a fertilized egg.
The cell is considered to be the basic part of the pathological processes of an organism.
Main article: Evolution
A central organizing concept in biology is that life changes and develops through evolution and that all life-forms known have a common origin. Introduced into the scientific lexicon by Jean-Baptiste de Lamarck in 1809, Charles Darwin established...