Punctuated equilibrium

Punctuated equilibrium is a theory of evolution which postulates that changes such as speciation occur very quickly, with long periods of little change (equilibria) in between. This accords well with what some perceive as the relative lack of intermediate forms in the fossil record in some evolutionary lines.

Simulations provide some insight into how this might work: the equilibrium periods show a gradual accumulation of neutral mutations, and the jump occurs when some beneficial combination of them reaches a certain threshold percentage (1/e²). On the other hand, speciation could also be triggered by classical means such as separation of populations.

A recent study on some trout that had been separated, in fact, showed that after only a few generations the two populations tended not to interbreed due to minor behavioral differences. Thus, even if they were remixed, the two groups would probably diverge genetically. This is much faster than anyone expected separation to occur.

The theory was proposed by Niles Eldredge[?] and Stephen Jay Gould in the 1970s. It relies heavily on Ernst Mayr's concept of peripatric speciation[?].

The theory of punctuated equilibrium is usually contrasted with phyletic gradualism[?], though critics, notably Richard Dawkins, have argued that phyletic gradualism[?] is merely a straw man. The actual differences between the various evolution theorists are not as large as the proponents of punctuated equilibrium have suggested, and the current debate is often more a debate on the relative degree of punctualism and gradualism than one between two fully different extremes.

External links:

• Talk Origins Archive (http://www.talkorigins.org/faqs/punc-eq)