Generally speaking, evolution is any process of growth, change or development. The word stems from the Latin evolutio meaning "unfolding" and prior to the late 1800s was confined to referring to goal-directed, pre-programmed processes such as embryological development. A pre-programmed task, as in a military maneuver, using this definition, may be termed an "evolution." While one can also speak of stellar evolution, cultural evolution or the evolution of an idea, the concept in the 20th century, was largely used in the sense of biological evolution, and refers to the change in the bodyplans of species over time and the appearance of new species. The remainder of this article discusses this concept of biological evolution, which had historically also been called transmutation, and the scientific theory that has developed around it.
An explanation as to how this evolution occurs is referred to as a theory of evolution. While transmutation was accepted by a sizeable number of scientists before 1859, it was the publication of Charles Darwin's The Origin of Species which provided the first cogent mechanism by which evolutionary change could persist: his mechanism of Natural selection. The evolutionary timeline outlines the major steps of evolution on Earth as expounded by this theory's proponents.
An essential component of evolutionary theory is the belief that biological evolution results in populations of organisms which are better adapted to their current environment than previous populations. Since, in the long run, environments always change, if successive generations did not develop adaptations which allowed them to survive and reproduce, species would simply die out as their biological niche dies out. Evolution therefore allows a species, as expressed in a given genetic line, to persist over greater spans of time.
Following the dawn of molecular biology in the 19th century, it was commonly believed that the mechanism for evolutionary change was through the mutagenesis of DNA. An essential component to evolutionary theory is that during the cell cycle, DNA is copied fairly, but not entirely, faithfully. When these rare copying errors occur, they are said to introduce genetic mutations of three general consequences relative to the current environment: good, bad, or neutral. By definition, individuals with "good" mutations will have an a stronger propensity to propagate, individuals with "bad" mutations will have less of a chance at successful reproduction, and those carrying "neutral" mutations will have neither an advantage nor a disadvantage. These definitions assume that the environment remains stable. Considered at the level of a single gene, these variations just described represent different genetic alleles. Following environmental change, alleles may retain their classification of good, bad, or neutral, or may shift into one of the other categories. Individuals carrying alleles formerly classified as neutral may now be "good" as they bear favourably adaptive mutations. Since neutral alleles can accumulate in the population without consequence while an environment is stable, they create a considerable reservoir for adaptability.
Although evolution depends on genetic variation over time, it is not purely restricted in cause to DNA mutation: bacteria can exchange genetic material via small DNA structures called plasmids.
Genetic variation is the first step in evolution cycle; complementary some form of selection acts on the various life forms to determine who passes on the genes, and how many progeny they produce.
The process of evolution has recently been put to use in computer science through genetic programming which uses the gene transmission mechanism as a search technique, and through evolutionary programming, which allows to parameterize computer programs to find an nearly optimal solution according to a goal function.
- Intelligent design, Intelligent Design Theory
- Theory of evolution
- Genetic programming