BIOLOGY OF CAVE ORGANISMS

Abstract

maintenance of standing genetic variability. Muller and Fisher both argued that the advantage lies in the capacity to put together favorable mutants that arise in different individuals (see Felsenstein, 1974, for an insightful discussion). The unique feature of Mendelian segregation and recombination, especially with polygenic inheritance, is to permit a maximum of potential variability with minimum standing variability. There are also advantages of sex that involve static rather than dynamic aspects of populationsthat don't depend on a changing environment. Muller's ratchet is one disadvantage of asexual reproduction (Felsenstein, 1974). I'll mention another. Recombination can reduce the mutation load by permitting several independently arising mutants to be picked off in one genetic death, which cannot happen in an asexual population (Crow, 1970). This is important if there is synergistic epistasis among harmful mutants, for example if there is rank-order selection. If natural selection is even a crude approximation to truncation selection, recombination can greatly decrease the mutation load. I don't argue for these views in preference to others; it may well be that no single mechanism will suffice, and that the reasons that recombination was invented in the first place may differ from those why it is perpetuated. We need to understand why rapidly reproducing parasites are sexual as well as long lived hosts. Yet, I believe that Hamilton's discussion merits serious attention. I was especially interested in his arguments for the advantages of a fitness topography that produces excess homozygosity. There is much food for thought in this book. There is discussion of both what is known and what needs to be known. It is interesting and, for the most part, easy reading. Thoughtfully, the editors have provided a glossary. There are even pictures of each of the groups. I enjoyed the chance to see what people whose work I have read and admired look like. Furthermore, the variety of shapes, stances, faces, and costumes provide an impressive illustration of human polymorphism.