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the theory of evolution stating that change in a species over time is partly the result of a process of natural selection, which enables the species to continually adapt to its changing environment.
A theory of biological evolution developed by Charles Darwin and others, stating that all species of organisms have developed from other species, primarily through natural selection. Also called Darwinian theory.
Darwinismthe theory of evolution formulated by Charles DARWIN that holds that different species of plants and animals have arisen by a process of slow and gradual changes over successive generations, brought about by NATURAL SELECTION. The essential points of Darwin's theory are:
- in organisms that reproduce sexually there is a wide range of variability, both within and between species.
- all living forms have the potential for a rapid rise in numbers, increasing at a geometric rate.
- the fact that populations usually remain within a limited size must indicate a ‘struggle for existence’ in which those individuals unsuited to the particular conditions operating at that time are eliminated or fail to breed as successfully as others (see FITNESS).
- the struggle for existence results in natural selection that favours the survival of the best-adapted individuals, a process described by Herbert Spencer (1820–93) in his Principles of Biology (1865) as the ‘survival of the fittest’.