Gradualism and Punctuated Equilibrium
I started researching this topic by skimming through my old (2003) textbook from my Human Evolution class that I took as an undergraduate. The authors make no mention of these two terms within the text. They do acknowledge that although slow rates of change are the typical units observed within the fossil record, rapid evolutionary events most likely happened, and the lack of evidence is a result of an incomplete fossil record ( Boyd and Silk 2003:22). The textbook for our seminar is a 2004 edition and dedicates several pages to gradualism and punctuated equilibrium. To me, this represents the variation in academia when it comes to challenging or accepting new concepts.
Gradualism may be defined as the process in evolution that accumulates small units of change at a steady rate, over long temporal periods. The gradual accumulation of new adaptations causes a genetic divergence of offspring from the parent, or ancestral species (Lewin and Foley 2004:52). Gradualism is therefore characterized as being a slow process that remains consistent and constant where change is cumulative within a species. Gradualism is essentially a fundamental part of the theory of Modern Synthesis (1942) that is a union of ideas which resulted from the differences that remained between strict Darwinism and evolutionary theory. Modern Synthesis has three principal components of which the first is gradualism. Although gradualism was originated by James Hutton in 1795, it traveled into Charles Lyell’s repertoire in the form of Unitarianism. It then influenced Charles Darwin and his theory of evolution. It is important to point out that
Punctuated Equilibrium essentially describes that species go through static periods with relatively little change that are accentuated by rapidly occurring modifications resulting in speciation. The species then return to a static period. Lewin and Foley (2004:52) indicate that separation of a daughter species from the ancestral species may still occur under punctuated equilibrium, but mainly it occurs through drifts in smaller, isolated populations. Steven Jay Gould and Niles Eldredge published their theory in 1972. Their work was influenced by Ernest Mayr, who also was a key contributor to Modern Synthesis, and Michael Lerner. One of the important differences between punctuated equilibrium and gradualism is how speciation is viewed. Punctuated equilibrium views adaptation as a possible result of speciation, while gradualism views it as a cause of speciation. In addition Gould and Eldredge view is similar to saltation only in the idea that change occurs rapidly. For Gould and Eldredge, adaptation occurs as result of speciation, but follows Darwinian fundamentals in doing so.
Gradualism and punctuated equilibrium may represent two different gears of the same mechanism; gradualism is the hour hand and punctuated equilibrium is the minute hand in which both are enclosed in a mechanism designed (or evolved) to measure time.
Gould and Eldredge (1993) celebrated the acceptance of their concept of punctuated equilibrium into the realm of theory. Can both theories actually coincide if some of the principal components to each contradict each other?
Boyd, Robert and Joan B. Silk
2003 How Humans Evolved. 3rd Edition.
Gould, Stephen J. and
1993 Punctuated Equilibrium Comes of Age. Nature. 18 November 1993 (366) :
Lewin, Roger and Robert A. Foley
2004 Principles of Human Evolution. 2nd Edition.