Encyclopedia of Evolution.pdf - Online Reading Center

punctuated equilibria
Gradualism was very clearly the idea that Charles Darwin
had in mind (see appendix, “Darwin’s ‘One Long Argument’: A
Summary of Origin of Species”). Darwin took a chance when
he declared that if evolution did not occur in gradual steps, one
could “rightly reject my whole theory.” Huxley (see Huxley,
Thomas Henry) told him, “You load yourself with unnecessary
difficulty …” by insisting on gradualism. According to the
defenders of punctuated equilibria, Huxley was right.
The difference between gradualism and punctuated equilibrium
is that the former posits gradual directional selection,
and the latter posits periods of stabilizing selection punctuated
by periods of rapid directional selection. Both models
appeal to the same Darwinian processes of natural selection,
plus some genetic drift. Though the proponents of each
approach defend their views passionately, the impression that
outside observers often get—that punctuationists are undermining
Darwinian evolution, and that the theory is in crisis—
is quite incorrect.
Further Reading
Eldredge, Niles. Reinventing Darwin: The Great Debate at the High
Table of Evolutionary Theory. New York: John Wiley, 1995.
Gould, Stephen J. The Structure of Evolutionary Theory. Cambridge,
Mass.: Harvard University Press, 2002.
———, and Niles Eldredge. “Punctuated equilibrium comes of age.”
Nature 366 (1993): 223–227.
Sheldon, P. R. “Parallel gradualistic evolution of Ordovician trilobites.”
Nature 330 (1987): 561–563.