Saltationism and Gradualism

In the explanation for the origin of new life forms throughout organic evolution, the temporal framework is very important. Two major positions have been offered to account for the process of speciation. Darwinism maintained that the emergence of a new species occurs slowly over a vast period of time in terms of slight variations and natural selection; as such, biological gradualism supplements geological gradualism in natural history. This interpretation upheld the continuity of organic evolution. In the 20th century, neo-Darwinism also supported biological gradualism, claiming that the process of speciation results from the slow accumulation of favorable minor changes in the genetic makeup of an organism. Over time, these positive slight alterations enhanced the adaptation, survival, and reproduction of a species in a changing environment. In sharp contrast, most sudden major mutations in genetic makeup are usually harmful to an organism and result in its sterility or death. If no members of a population can adapt to changes in the environment, then the population becomes extinct. Because biological evolution has been occurring for about 4 billion years, it is generally held that there has been sufficient time for organic history to account for the staggering creativity of life forms in terms of biological gradualism. Nevertheless, the fossil record attests to the fact that most of the species that have ever existed on the earth slowly or suddenly became extinct.

There is no consensus among naturalists concerning the conceptual issue of time and speciation. Although Charles Darwin supported evolutionary gradualism, his contemporary Thomas Henry Huxley argued for a form of saltationism. Huxley maintained that the appearance of a new species represents a major leap, or saltation, in organic evolution. Therefore, in sharp contrast to Darwin himself, Huxley did not claim that biological history represents an organic continuum. To some naturalists, the incomplete fossil record suggested that species both appear and vanish suddenly throughout evolutionary time. In the middle of the 20th century, the saltationism position was revived by Richard B. Goldschmidt in his controversial book The Basis of Evolution (1940). In this work, the geneticist claimed that the change from species to species cannot be explained in terms of the accumulation of atomistic changes in an organism (microevolution). Instead, Goldschmidt favored macroevolution with its quantum speciation. Consequently, he put forward his “hopeful monster” hypothesis, which argued that macro-evolution (not microevolution) resulted in the instantaneous appearance of a new species and even higher taxonomie groups.

More recently, Niles Eldredge and Stephen Jay Gould presented their “punctuated equilibrium” hypothesis, which claims that a new species appears in a small isolated population during a relatively short period of geological time (only several tens of thousands of years). Unfortunately, this interpretation of “rapid” evolution, along with the incomplete fossil record and alleged lack of transitional [Page 1125]fossils in the geological column, provided biblical fundamentalists and religious creationists with a basis they can use for discrediting the immense age of the earth in general and the process of organic evolution in particular.

For scientists, however, geological time and biological time are linked in organic evolution and the process of speciation. This remains the case regardless of whether or not rates of evolutionary change have varied greatly throughout those vast eras of time represented by earth history.

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