PROCEEDINGS OF THE SIXTH BERKELEY SYMPOSIUM ON MATHEMATICAL STATISTICS AND PROBABILITY, VOLUME 5: DARWINIAN NEO‐DARWINIAN, AND NON‐DARWINIAN EVOLUTION

It is a tribute to the organizers of this distinguished series of symposia on mathematical topics that by recognizing and emphasizing the essence of a biological problem rather than simply associated techniques, they have produced a volume that no one seriously interested in modern evolutionary theory can afford to ignore. It is a commentary on the current status of the neutral versus selectionist argument that despite the inclusion of papers by distinguished proponents of virtually every viewpoint, there is no clear progress toward consensus, nor any suggestion of unequivocal tests. The difficulty remains that the essential variables of neutral theory, such as effective population size (NeX), selective values for alternative alleles at enzyme loci, and migration rates between Mendelian populations, are essentially unknown for almost any natural population. It would seem, too, that much of the controversy emphasizes viewpoints rather than scientific debate. It seems quite reasonable that many base changes in DNA molecules may be neutral, provided they do not affect the synthesis or properties of the proteins coded for. On the other hand, as Ayala documents, mutations which do affect the protein product are unlikely to be neutral. Ecological geneticists interested in the process of adaptation to environment are little interested in point mutations which never make their appearance felt, and tend to dismiss the neutral theory. Molecular geneticists, on the other hand, as fundamentally interested in a different question, and readily accept many of the neutralists' arguments. The first four papers in this volume are largely expository, and provide an excellent orientation for the rest. Crow reviews neutral theory and argues for its importance with regard to most changes in DNA, arguing that most DNA is noninformational. Both this article and the following one by Stebbins and Lewontin stress the point that some changes are certainly adaptive, while others are clearly due to chance. The difference between viewpoints is in the relative importance ascribed to each. The two articles provide excellent counterpoint to each other. The contribution of Kimura and Ohta, whose authors were not present at the symposium, represents the view of, probably the most convinced of the neutralists. Kimura is responsible for most of the recent mathematical basis of neutral theory. Despite their strong belief that most protein polymorphisms are transient rather than permanent, their statement that the transient existence may last millions of years points up the difficulties involved in putting such a theory to test. The remainder of the volume presents a fascinating reading list, especially MacIntyre's technique for distinguishing homologous enzymes of closely related species, and the papers of Allard and Kahler, of Ayala, of Bodmer and CavalliSforza, and of Ewens. The fact is that for pairs of neutral alleles, despite the fact that the individual allele frequencies are expected to be on a random walk between 0 and 1, the expected value of the disequilibrium is zero, and this value is not often experimentally observed (Allard and Kahler). The neutral theory wriggles free again, however, since D is subject to statistical variation. Bodmer and Cavalli-Sforza dispute, as many have, Kimura's adoption of Haldane's computations regarding the cost of natural selection. These load calculations have been one of the main arguments utilized by neutral theorists, but depend on the assumption of independent action of different loci on fitness. They dispute as well the arguments of King and Jukes, also represented in this volume. Their concluding sentence may well summarize the volume, "The major question of the extent to which new mutants are or are not associated with selective differences is, apparently, no nearer resolution today than it was well before the recent revival of discussion about 'non-Darwinian' evolution." If evolution is neutral, then geographically iso'Proceedings of the Sixth Berkeley Symposium on Mathematical Statistics and Probability, Volume 5: Darwinian, Neo-Darwinian, and NonDarwinian Evolution, April 9-12, 1971. Lucien M. Le Cam, Jerzy Neyman, and Elizabeth L. Scott, Editors. University of California Press, Berkeley and Los Angeles. 1972.