SPECIATION AND MACROEVOLUTION

Species and higher taxa represent, phenomenologically, two very different levels in the hierarchical organization of the living world. Ever since there has been a concept of evolution, there has been the problem how one can get from the species level to that of the higher categories. Darwin, the champion of gradualism, declared that it was a purely quantitative problem. If one would simply pile enough small differences on top of each other, one would eventually get something that is qualitatively different, that is, a higher taxon or an evolutionary novelty. Why Darwin was so intent on defending gradualism is something I do not want to take up at this time (Gruber, 1974; Stanley, 1979; Ospovat, 1981). But Darwin, at that time, was virtually alone in this insistence on gradualism (as far as I know the literature). Virtually all other evolutionists of his period were so impressed by the gaps between genera and by the even greater gaps among the higher taxa that they felt they could not do without saltations. T. H. Huxley was characteristic of this thinking. Saltationism became even more popular after the publications of Bateson (1894) and de Vries (1901-1903), even though there were occasional voices (e.g., Scott, 1894) championing gradual evolution. Even though there was a last flareup of saltationism in the 1940s and 1950s (represented by Goldschmidt [1940], Willis [1940], and Schindewolf [1950]), gradualism was triumphant in the evolutionary synthesis. I want to point out, however, that it was, on the whole, a gradualism in the vertical (Lamarckian) tradition. It was simply a thinking in terms of phyletic lines that gradually and inexorably moved upward to ever better adaptations or ever greater specializations. The Darwinian "horizontal" tradition of an origin of diversity, that is of a multiplication of species, and the role of this diversification in macroevolution was totally ignored. When one studies the writings of "Darwinian" paleontologists, one discovers that in their argumentation they proceed directly from the genetic variation-mutation level-to that of macroevolutionary processes (new higher taxa, evolutionary novelties). The same was true for the geneticists who (except for Dobzhansky and a few others with a natural history background) moved straight from the gene level to that of macroevolution. It is only in the writings of the naturalists, particularly the zoologists, that the total transition from the gene level to that of macroevolutionary processes is considered by inserting and analyzing the role of the species, in the transition from population to species to higher taxon. The difference between the thinking of the geneticists-paleontologists on one hand, and Darwin and the naturalists on the other hand, is far more fundamental than is appreciated by most evolutionists. If we define evolution as changes in adaptation and diversity, then the students of adaptation deal with what we might call the vertical dimension of evolution, while the students of diversity deal with the horizontal dimension, that is with the changes of populations in latitude and longitude. Actually, of course, both processes take place simultaneously, but most workers in the different subdisciplines of evolutionary biology have paid attention only to one of the two dimensions. Paleontologists, when studying macroevolution, traditionally never come to grips with the problem of the origin of the taxa or types that evolved "higher" or experienced adaptive radiations. Simpson (1944), for example, makes no reference to species or speciation