BIOL 1123 Lecture Notes - Lecture 24: Generation Time, Speciation

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There are a few issues on deciding which is true, as the following: Gradualism: suggests that each new species evolves continuously over long spans of time. The main idea is that large phenotypic differences that produce new species are due to the accumulation of many small genetic changes. Punctuated equilibrium: contrasting to gradualism, this believes that the tempo of evolution is more sporadic since species exist relatively unchanged for many generations (when they are in equilibrium). These longs periods of equilibrium are punctured by relatively short periods on an evolutionary timescale in which evolution occurs more rapidly perhaps because of environmental changes or the founder effect or new mutations. Only a small number of new mutations are required to alter phenotypic characteristics, eventually producing a group of individuals that make up a new species. In the same way, events such as changes in chromosome number and alloploidy can abruptly create individuals with new phenotypic traits.

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