Evolution is the process of change in all forms of life over generations, and evolutionary biology is the study of how evolution occurs. An organism inherits features (called traits) from its parents through genes. Changes (called mutations) in these genes can produce a new trait in the offspring of an organism. If a new trait makes these offspring better suited to their environment, they will be more successful at surviving and reproducing. This process is called natural selection, and it causes useful traits to become more common. Over many generations, a population can acquire so many new traits that it becomes a new species.
The understanding of evolutionary biology began with the 1859 publication of Charles Darwin's On the Origin of Species.
In addition, Gregor Mendel's work with plants helped to explain the hereditary patterns of genetics. This led to an understanding of the mechanisms of inheritance. Further discoveries on how genes mutate, as well as advances in population genetics explained more details of how evolution occurs. Scientists now have a good understanding of the origin of new species (speciation). They have observed the speciation process happening both in the laboratory and in the wild. This modern view of evolution is the principal theory that scientists use to understand life.
Darwin deduced that since organisms produce more offspring than their environment could possibly support, there must be a competitive struggle for survival - only a few individuals can survive out of each generation. Darwin realized that it was not chance alone that determined survival. Instead, survival depends on the traits of each individual and if these traits aid or hinder survival and reproduction. Well-adapted, or "fit", individuals are likely to leave more offspring than their less well-adapted competitors. Darwin realized that the unequal ability of individuals to survive and reproduce could cause gradual changes in the population. Traits that help an organism survive and reproduce would accumulate over generations. On the other hand, traits that hinder survival and reproduction would disappear. Darwin used the term natural selection to describe this process.