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Main article: Macroevolution
Macroevolution refers to large-scale changes in gene-frequencies in a population over a long period of time, and is usually taken to refer to events that result in speciation, the evolution of a new species. While microevolution has been demonstrated in the laboratory to the satisfaction of most observers, macroevolution has to be inferred from the fossil record and the traits of extant organisms. Its precise mechanisms are an active topic of discussion amongst scientists.Main article: Speciation
Speciation is the creation of two or more species from one. There are various mechanisms by which this may take place. Allopatry begins when subpopulations of a species become isolated geographically, for example by habitat fragmentation or migration. Sympatry is when new species emerge in the same geographic area. Parapatry is in between the extremes of allopatry and sympatry.
Main article: Extinction
Extinction is the disappearance of species, (i.e. gene pools). The moment of extinction is generally considered to be the death of the last individual of that species. Extinction is not an unusual event in geological time—species are created by speciation, and disappear through extinction.
Main article: Evolutionary biology
The study of evolution and the development of related theory is called evolutionary biology. Notable contributors to evolutionary biology include:
Notable popularizers of evolution whose primary research isn't within evolutionary biology include:
Main article: History of evolutionary thought
The idea of biological evolution has existed since ancient times, but the modern theory wasn't established until the 18th and 19th centuries, with scientists such as Jean-Baptiste Lamarck and Charles Darwin. Darwin greatly emphasized the difference between his two main points: establishing the fact of evolution, and proposing the theory of natural selection to explain the mechanism of evolution.
While transmutation of species 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 theory of natural selection. The evolutionary timeline outlines the major steps of evolution on Earth as expounded by this theory's proponents.
Darwin's theory, though it succeeded in profoundly shaking scientific opinion regarding the development of life (and indeed resulted in a small social revolution), could not explain several critical components of the evolutionary process. Namely, he was unable to explain the source of variation in traits within a species, and he could not provide a mechanism whereby traits were passed faithfully from one generation to the next.
These questions were not settled until the end of the 19th century, beginning with the work of an Austrian monk named Gregor Mendel, who outlined, through a series of ingeniously devised experiments, a model for inheritance of traits based on the fundamental unit of the gene. Mendel's work was unappreciated at the time and largely ignored by a biological community that was baffled by the mathematical nature of his theories. When it finally gained widespread acknowledgement, it led to a storm of conflict between Mendelians and biometricians, who insisted that the great majority of traits important to evolution must show continuous variation that was not explainable by Mendelian analysis.
Eventually, the Mendelians won out, and a series of papers in the 1930s and 1940s led to the development of the modern synthesis, which brought together Darwin's theories of natural selection with Mendel's theories of inheritance via genes.
In the 1940s, Avery, McCleod and McCarty definitively identified deoxyribonucleic acid (DNA) as the "transforming principle" responsible for transmitting genetic information. In 1953, Francis Crick and James Watson published their famous paper on the structure of DNA, based on the research of Rosalind Franklin. These developments ignited the era of molecular biology and transformed the understanding of evolution into a molecular process: the mutation of segments of DNA.
In the mid-1970s, Motoo Kimura formulated the neutral theory of molecular evolution, firmly establishing the importance of genetic drift as a major mechanism of evolution.
Debates have continued within the field. One of the most prominent outstanding debates is over the theory of punctuated equilibrium, a theory propounded by Stephen Jay Gould to explain the paucity of transitional forms between phyla.
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