Gould, Stephen J. “Is a new and general theory of evolution emerging?.” In Self-Organizing Systems , pp. 113-130. Springer, Boston, MA, 1987.
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The “modern synthetic” view of evolution has broken down, at least as an exclusive proposition, on both of its fundamental claims: (1) “extrapolationism” (gradual substitution of different alleles in many genes as the exclusive process underlying all evolutionary change) and (2) nearly exclusive reliance on selection leading to adaptation. Evolution is a hierarchical process with complementary, but different modes of change at its three large-scale levels: (a) variation within populations, (b) speciation, and (c) very long-term macroevolutionary trends. Speciation is not always an extension of gradual, adaptive allelic substitution, but may represent, as Goldschmidt argued, a different style of genetic change—rapid reorganization of the genome, perhaps nonadaptive. Macroevolutionary trends do not arise from the gradual, adaptive transformation of populations, but usually from a higher-order selection operating upon groups of species. Individual species generally do not change much after their “instantaneous” (in geological time) origin. These two discontinuities in the evolutionary hierarchy can be called the Goldschmidt break (change in populations is different from speciation) and the Wright break (speciation is different from macroevolutionary trending that translates differential success among different species).
A new and general evolutionary theory will embody this notion of hierarchy and stress a variety of themes either ignored or explicitly rejected by the modern synthesis: e.g., punctuational change at all levels, important nonadaptive change at all levels, control of evolution not only by selection, but equally by constraints of history, development, and architecture—thus restoring to evolutionary theory a concept of organism.