Particulate inheritance

Abstract: Huxley coined the phrase, the “evolutionary synthesis” to refer to the acceptance by a vast majority of biologists in the mid-20th Century of a “synthetic” view of evolution. According to this view, natural selection acting on minor hereditary variation was the primary cause of both adaptive change within populations and major changes, such as speciation and the evolution of higher taxa, such as families and genera. This was, roughly, a synthesis of Mendelian genetics and Darwinian evolutionary theory; it was a demonstration that prior barriers to understanding between various subdisciplines in the life sciences could be removed. The relevance of different domains in biology to one another was established under a common research program. The evolutionary synthesis may be broken down into two periods, the “early” synthesis from 1918 through 1932, and what is more often called the “modern synthesis” from 1936-1947. The authors most commonly associated with the early synthesis are J.B.S. Haldane, R.A. Fisher, and S. Wright. These three figures authored a number of important synthetic advances; first, they demonstrated the compatibility of a Mendelian, particulate theory of inheritance with the results of Biometry, a study of the correlations of measures of traits between relatives. Second, they developed the theoretical framework for evolutionary biology, classical population genetics. This is a family of mathematical models representing evolution as change in genotype frequencies, from one generation to the next, as a product of selection, mutation, migration, and drift, or chance. Third, there was a broader synthesis of population genetics with cytology (cell biology), genetics, and biochemistry, as well as both empirical and mathematical demonstrations to the effect that very small selective forces acting over a relatively long time were able to generate substantial evolutionary change, a novel and surprising result to many skeptics of Darwinian gradualist views. The later “modern” synthesis is most often identified with the work of Mayr, Dobzhansky and Simpson. There was a major institutional change in biology at this stage, insofar as different subdisciplines formerly housed in different departments, and with different methodologies were united under the same institutional umbrella of “evolutionary biology.” Mayr played an important role as a community architect, in founding the Society for the Study of Evolution, and the journal Evolution, which drew together work in systematics, biogeography, paleontology, and theoretical population genetics.

Abstract: Genetics has had a chequered career in the hundred years that have elapsed since Mendel published the paper in which he laid the methodological as well as the conceptual foundation for the science as we have come to know it. For the first thirty years or so the paper was ignored. It was ignored because it was out of keeping with the times, not perhaps so much in its concept of particulate inheritance (with which Galton at any rate was toying at one stage), but in the nature of its experimental approach. With the twentieth century both concepts and methods were accepted and developed: the new science, conceived in Mendel’s frustration and born into Bateson’s and Pearson’s strife, grew lustily. Yet for several further decades genetics was still not accepted into the main stream of biology. True, it attested the power of its techniques by the speed of its growth and it developed a theoretical structure more reminiscent of the physical sciences than of its contemporary biology. It opened up new vistas and in principle it promised to shed new light on the central problems of biology—evolution and development. But in practice it seemed to remain remote, dealing in its own currency of patho­logical effects instead of constructive adaptations, and abstract entities instead of analysable processes. Happily this has changed, as our Symposium bears witness. Genetics is no longer isolated, but at the core of biology. It is becoming recognized—albeit at times a little reluctantly—as having a necessary, if not of itself sufficient, part to play in our approach to all the great problems of biology. This change has come about primarily because genetics itself has grown, and grown in two directions. One of these has been in the analysis of mechanisms and materials of heredity. The abstract factor which Mendel postulated to explain the relation he found between parent and offspring has become a message coded into the macromolecule of DNA by the arrangement of its bases, and the hypothetical connexion between genotype and phenotype is materializing in RNA , cytoplasmic elements and protein synthesis. We are moving into the position where we can begin to give an account of development and its associated differentiation.