Phyletic gradualism
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Phyletic gradualism is a model of evolution which theorizes that most speciation is slow, uniform and gradual.[1] When evolution occurs in this mode, it is usually by the steady transformation of a whole species into a new one (through a process called anagenesis). In this view no clear line of demarcation exists between an ancestral species and a descendant species, unless splitting occurs. The theory is contrasted with punctuated equilibrium.
History
The word phyletic derives from the Greek φυλετικός phūletikos, which conveys the meaning of a line of descent.[2] Phyletic gradualism contrasts with the theory of punctuated equilibrium, which proposes that most evolution occurs isolated in rare episodes of rapid evolution, when a single species splits into two distinct species, followed by a long period of stasis or non-change. These models both contrast with variable-speed evolution ("variable speedism"), which maintains that different species evolve at different rates, and that there is no reason to stress one rate of change over another.[3][4]
See also
References
- ^ Eldredge, N. and S. J. Gould (1972). "Punctuated equilibria: an alternative to phyletic gradualism" In T.J.M. Schopf, ed., Models in Paleobiology. San Francisco: Freeman Cooper. p. 84.
- ^ φυλετικός phūletikos originates from φυλέτης phūletēs "one of the same tribe," from φυλή phulē, "clan, race, people", derived from φύεσθαι phuesthai, "to descend, to originate."
- ISBN 0-393-31570-3
- ^ Futuyma, Douglas. 2005. Evolution. Sunderland MA: Sinauer Associates, pp. 86-89
- ^ Charles Darwin, 1859. On the origin of species London: John Murray. 1st edition, p. 313.
- ^ Charles Darwin, 1869. The Origin of Species London: John Murray. 5th edition, p. 551.
External links
- Media related to Phyletic gradualism at Wikimedia Commons
- The distinction between phyletic gradualism and punctuated equilibrium models - by Mark Ridley