The Modern Synthesis as a Limited Consensus 563
that the pattern itself might be built by higher-level sorting, operating through the
differential success of certain kinds of species!
The formation of many geographically isolated and most genetically
isolated species is thus without any bearing upon the main processes of
evolution ... Much of the minor systematic diversity to be observed in
nature is irrelevant to the main course of evolution, a mere thrill of variety
superimposed upon its broad pattern. We may thus say that, while it is
inevitable that life should be divided up into species, and that the broad
processes of evolution should operate with species as units of organization,
the number thus necessitated is far less than the number, which actually
exist. Species-formation constitutes one aspect of evolution; but a large
fraction of it is in a sense an accident, a biological luxury, without bearing
upon the major and continuing trends of the evolutionary process (Huxley,
1942, p. 389).Amidst this attempt to relegate the origin of the primary unit of
macroevolution to irrelevancy at larger scales, one prominent voice within the Syn-
thesis spoke up for the centrality of speciation in constructing large-scale pattern.
In a cautious, but prophetic statement, Ernst Mayr (1963, p. 587) wrote: "To state
the problems of macroevolution in terms of species and populations as 'units of
evolution' reveals previously neglected problems and sometimes leads to an
emphasis on different aspects." (Much of macroevolutionary theory, as developed
later, begins with this proposition, and Mayr therefore becomes an inspiration—
ironically in a sense, for several key concepts in this developing body of thought
have challenged other aspects of the Synthesis that Mayr so strongly championed.
For example, the theory of punctuated equilibrium rests upon a proper translation
into geological time of Mayr's peripatric theory of speciation—see Eldredge and
Gould, 1972, and Chapter 9.
Directly refuting Huxley's charge that speciation only ranks as a frill and
luxury in the overall pattern of evolutionary change, Mayr wrote:
I feel that it is the very process of creating so many species, which leads to
evolutionary progress. Species, in the sense of evolution, are quite
comparable to mutations. They also are a necessity for evolutionary
progress, even though only one out of many mutations leads to a significant
improvement of the genotype. Since each coadapted gene complex has
different properties and since these properties are, so to speak, not
predictable, it requires the creation of a large number of such gene
complexes before one is achieved that will lead to real evolutionary
advance. Seen in this light, it appears then that a prodigious multiplication
of species is a prerequisite for evolutionary progress... Without speciation,
there would be no diversification of the organic world, no adaptive
radiation, and very little evolutionary progress. The species, then, is the
keystone of evolution (1963, p. 621).