From Freeman and Herron (2004):
And a very important part in relation to what I mentioned in an earlier post, they quote Erwin and Anstey:
Erwin, D. & Anstey, R. (1995). Speciation in the fossil record. In D. H. Erwin and R. L. Anstey (Eds.). New Approaches to Speciation in the Fossil Record. New York: Columbia University Press.
Freeman, S. & Herron, J. (2004). Evolutionary Analysis. (3rd ed.). Upper Saddle River: Prentice Hall.
Quote:One of the prominent patterns in the history of life is that new morphospecies appear in the fossil record suddenly and then persist for millions of years without apparent change. In many cases, evolutionary innovations seem to arise at the same time as new species. As a result, morphological evolution in some groups seems to consist of long periods of stasis that are occasionally punctuated by speciation events that appear instantaneously in geological time. Gradual series of transitional forms do occur, but in some groups they are relatively rare.
Darwin (1859) was well aware of these observations and considered them a problem for his theory. Because his ideas were presented in opposition to the Theory of Special Creation, which predicts the instantaneous creation of new forms, Darwin repeatedly emphasized the gradual nature of evolution by natural selection. He attributed the sudden appearance of new taxa to the incompleteness of the fossil record and predicted that as specimen collections grew, the apparent gaps between fossil forms caused by stasis (and punctuated by sudden jumps) would be filled in by forms showing gradual transitions between morphospecies. For a century thereafter, most paleontologists followed his lead.
In 1972, however, Niled Eldredge and Stephen J. Gould broke with tradition by claiming that stasis is a real pattern in the fossil record and that most morphological change occurs during speciation. They called their proposal the theory of punctuated equilibrium. The theory and its implications were hotly debated for 20 years, but both proponents and critics now agree that most of the disagreements stemmed from differences in time scales. Biologists routinely observe changes in morphology within and between populations over tens or hundreds of years and document gradual change. But if a paleontologist studied morphological change in the same groups over a million-year interval, the change would appear large and sudden.
And a very important part in relation to what I mentioned in an earlier post, they quote Erwin and Anstey:
Quote:Erwin and Anstey's conclusion was that "paleontological evidence overwhelmingly supports a view that speciation is sometimes gradual and sometimes punctuated, and that no one mode characterizes this very complicated process in the history of life". Furthermore, Erwin and Anstey noted that a quarter of the studies reported a third pattern: gradulism and stasis.
Erwin, D. & Anstey, R. (1995). Speciation in the fossil record. In D. H. Erwin and R. L. Anstey (Eds.). New Approaches to Speciation in the Fossil Record. New York: Columbia University Press.
Freeman, S. & Herron, J. (2004). Evolutionary Analysis. (3rd ed.). Upper Saddle River: Prentice Hall.
