Genes and the Evolutionary Synthesis

My intention in this and the following chapter is simply to clarify what a few of the better known architects of the synthesis actually had to say about how the entire spectrum of genes through phyla really fits together. I have chosen books rather than a potpourri of articles from the (possibly) more “technical” scientific literature, for precisely this reason: it is in the books that we find the coherent, integrated statements. And each of the four books singled out for particularly close analysis—Genetics and the Origin of Species (Dobzhansky 1937a); Genetics and the Origin of Species second edition (Dobzhansky 1941); Systematics and the Origin of Species (Mayr 1942); and Tempo and Mode in Evolution (Simpson 1944)—is a truly coherent, though not necessarily smoothly linear, argument. In each, some parts seem more vital to the flow of argument than others, but it is clear to the reader from the outset that each is a complete book and not a disjointed melange of unrelated ideas. Then, too, the contents of each author’s papers are to a great extent reflected in the respective books. It is apparent, for example, that Dobzhansky was publishing a variety of papers in the 1930s (many were in his “Genetics of Natural Populations” series republished in a single volume in 1981 by Lewontin et al.) which he liberally drew upon for illustrative material in Genetics and the Origin of Species. The other sorts of papers Dobzhansky was publishing seem to be byproducts of his thinking and research for the various editions of his book. Examples are his papers on species definitions (1935) and isolating mechanisms (1937b) and his theory of the origin of isolating mechanisms by reinforcement (1940). The choice of the four particular books for special treatment in this volume needs further comment. I have omitted such nonconformist works as Robson and Richards (1936), Willis (1940), and Goldschmidt (1940) precisely because they have been almost universally considered as falling outside the limits of the synthesis. The main historical effect of such books (especially Goldschmidt’s) seems to have been as irritants.

LINKAGE MODIFICATION WITH MIXED RANDOM MATING AND SELFING: A NUMERICAL STUDY

ABSTRACT Although recombination cannot increase under conditions of random mating or complete selfing in regimes of constant selection, with mixed random mating and selfing, selection for increased recombination can occur. For some fitness regimes there may be selection for reduced recombination with both low and high degrees of selfing but selection for increased recombination with moderate degrees of selfing. With some fitness regimes there is a historical effect: depending on which equilibrium a population starts from, there may be selection for either increased or decreased recombination. In other cases the direction of selection may be determined by the present state of individuals within the population. If recombination is already fairly limited, there may be selection for further reduction. If recombination is already fairly frequent, there may be selection for increased recombination. For certain symmetric viability systems there may be an intermediate value of the recombination fraction between 0 and 0.5 toward which the population will evolve. Although it is not yet possible to classify precisely those fitness matrices that can exhibit selection for increased recombination, it does appear that selection for increased recombination can occur only if at least two of the double homozygotes are less fit than would be expected on the basis of a comparison of the fitnesses of the single and double heterozygotes on an additive scale.

VIII. Observations on the historical evidence respecting the Implication of Lord Mounteagle as a Conspirator in the Gunpowder Treason. Communicated to the Society of Antiquaries by David Jardine, Esq., in a Letter to Sir Henry Ellis, K.H., F.R.S., Secretary

The perusal of the curious letters of Thomas Winter and Lord Mounteagle, lately discovered by Mr. Bruce, suggested to my mind some remarks upon the historical effect of those letters which I have already submitted through you to the Society of Antiquaries. In my former communication I fully explained my reasons for thinking that the letter of Lord Mounteagle published by Mr. Bruce does not afford a solution of the problem respecting that nobleman's implication in the Gunpowder Plot; and I further expressed an opinion that the tendency of the evidence we now possess is to exonerate his character from the suspicion of having been in the first instance a party to the plot, and having afterwards betrayed his companions.