Evolution is the change that species undergo over time. To be more specific, evolution is the change in the gene pools of living populations of species which occurs over time. A hereditary unit that can be passed on unaltered for many generations is a gene and the set of all genes in a species or population is the gene pool. The first point stated by the theory of evolution, and possibly the most important, is that all life forms have developed from other species. It also states that all living things are related to one another to different degrees and that they all share common ancestors. The third point is that all life on Earth has a common origin. To make it simpler, all life arose from a once existing original life form. The process by which one species evolves into another requires genetic mutations, or changes, is the fourth and final statement in the theory of evolution. In order for evolution to occur, three main mechanisms must occur, natural selection, genetic drift, and mutation. Natural selection is the process by which traits that provide a reproductive advantage tend to increase in frequency in a given species over time. Also, traits that put individuals at a disadvantage most likely decrease over time. Genetic drift is the process in which traits change over time merely by chance, as to predetermined change in natural selection. A mutation is any change in the DNA base sequence of a gene, which occurs in both natural selection and genetic drift. Evolution can be found in fossil records and chemical and structural similarities. Genetic changes over generations and geographic distribution of related species are also two great pieces of evidence supporting the theory of evolution.
Probably the most popular evidence for evolution is the numerous fossils found over time. The remains of plants and animals found in sedimentary rock deposits give scientists an indisputable record of past changes through time.