Natural selection

Natural selection is the mechanism of evolution proposed by Charles Darwin and generally accepted by the scientific community as the best explanation of speciation as evidenced in the fossil record. It is also sometimes referred to as "Darwinism", usually by its critics.

The theory starts from the premise that an organism's traits vary in a nondeterministic? way from parent to offspring, a process called "individuation" by Darwin. The theory of natural selection does not make any specific claims as to how this process works, although more recent scientific discoveries in genetics indicate mutation is at least one cause.

If a particular variation makes the offspring which manifest it better suited to survival or to successful reproduction, that offspring and its descendents will be more likely to survive than those offspring without the variation. The original traits, as well as any maladaptive variations, will disappear as the offspring who carry them are replaced by their more successful relatives.

Therefore, certain traits are preserved due to the selective advantage they provide to their holders, allowing the individual to leave more offspring than individuals without the trait(s). Eventually, through many iterations of this process, the organism will develop into a different organism by slow degrees.

What makes one trait more likely to succeed is highly dependent on environmental factors, including the species' predators, food sources, physical environment, and so on. When members of a species become separated, such as geographically, they face different environments, and tend to develop in different directions. After a long period of time, their traits will have developed along different paths to such an extent that they can no longer interbreed, at which point they are considered separate species. This is why a species will sometimes separate into multiple species, rather than simply being replaced by a newer form of the species.

Natural selection can be expressed as the following general algorithm:

1. IF there are variations between entities, and
2. IF these variations are heritable, and
3. IF one variant is more successful at a given task, and
4. IF that relative success allows more copies of the entity to be passed on to the next generation,
5. THEN selection will produce change over time (Evolution!)

Note that the above algorithm is made with no explicit reference to biological entities. Thus, a form of natural selection could occur in the non-biological realm. Note also that this formulation does not rule out selection occurring at all biological levels (e.g. gene, organism, group). Nor does it matter what the cause of variation is: some creationists, for example, generally accept that evolution occurs, but posit that God causes the changes that lead to it.

Darwin first outlined his theory in two unpublished manuscripts written in 1842 and 1844 and more fully developed it for publication in The Origin of Species, especially Chapter 4.

See also; [artifical selection]?, sexual selection, evolution

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