BIOSYSTEMATICS: AN AVENUE TOWARDS UNDERSTANDING EVOLUTION

Abstract

SummaryThe distinctive feature of biosystematics is considered to be its emphasis upon the processes responsible for differences between taxa, rather than the differences themselves. A progress report on our knowledge of these processes can be summarized as follows. With respect to divergent adaptations to different environments, we understand well their genetic basis, and are now ready to analyze them in terms of gene action in development and metabolism. A valuable new tool for this purpose is the study of isozyme differences by gel electrophoresis. With respect to the origin of barriers of reproductive isolation that play a large role in the origin of species, we need further tests of the hypothesis that chromosomal repatterning is established through the action of natural selection, because of the different adaptive values of differing clusters of linked genes. A new hypothesis that also needs testing is that hybrid inviability or sterility may be produced by disharmonious interaction between genes that code for different subunits of the same multimer enzyme. Valuable studies of hybridization are directed toward determining the importance of transgressive segregation in the origin of new characters. Our understanding of differences in karyotypes must now be based upon the demonstrated fact that even diploid organisms contain large stretches of chromosomal DNA that is duplicated in tandem fashion. With respect to major trends of evolution, several examples are cited which indicate that the origin of genera and other higher categories can take place through an extension of the processes mentioned earlier. An important fact in this connection is that many natural populations of plants contain hidden genetic variation with respect to such basic characteristics as the number of parts of a flower.