The Mechanism of Creative Evolution

Since the rediscovery of Mendel's papers in 1900, the science of genetics has grown rapidly. Not only has there been a rich increase in our factual knowledge but there has also appeared a new and elaborate vocabulary. The complexity of the former and the unfamiliarity of the latter has made the science of genetics an almost unknown land for all who are not specialists in that field. It is, therefore, with pleasure that one finds a presentation of the subject at the same time so full of important scientific data and yet readily intelligible to the average reader. Dr. Hurst has been actively engaged in research in the field of genetics for thirty years, investigating crucial problems in a wide variety of forms in most of the countries of the world. He speaks with authority and writes lucid, understandable English. Beginning with a brief review of the historical background of genetics, he proceeds at once to a discussion of chromosomes and their relationship to cells. The behavior of chromosomes is stressed, and there is a brief summary of modern experimental study of them. In not too technical language, the analysis of chromosomes into their component genes is presented, with emphasis upon the position of the gene in the chromosome. The constancy in the number of chromosomes in any particular species is emphasized, and Dr. Hurst offers this fact as the basis for a solid description of the characteristics of a species. It is his belief that this criterion is a more adequate measure of a species than is any other series of descriptive facts. While in many instances the genetic species coincides with the Linnean species this is not always so and he believes that the former is a more valid unit than is the latter. The experimental study of genes is no less adequately treated. The evidence for translocation of genes, extra chromosomes, hybridization and crossing, and for mutations, both natural and experimental, are all briefly but clearly presented. There follows a consideration of the evidence showing the relationship between genes and physical characters. To this important field, Dr. Hurst has contributed very valuable data concerning the genetic behaviour of attributes and abilities in man. He has shown that these, no less than physical characters, obey genetic law. The last five chapters in the book comprise, perhaps, the most interesting section. Here are presented a number of interesting generalizations …