%0 Journal Article %T Sex and Speciation: Drosophila Reproductive Tract Proteins¡ª Twenty Five Years Later %A Rama Singh %A Santosh Jagadeeshan %J International Journal of Evolutionary Biology %D 2012 %I Hindawi Publishing Corporation %R 10.1155/2012/191495 %X The protein electrophoresis revolution, nearly fifty years ago, provided the first glimpse into the nature of molecular genetic variation within and between species and showed that the amount of genetic differences between newly arisen species was minimal. Twenty years later, 2D electrophoresis showed that, in contrast to general gene-enzyme variation, reproductive tract proteins were less polymorphic within species but highly diverged between species. The 2D results were interesting and revolutionary, but somewhat uninterpretable because, at the time, rapid evolution and selective sweeps were not yet part of the common vocabulary of evolutionary biologists. Since then, genomic studies of sex and reproduction-related (SRR) genes have grown rapidly into a large area of research in evolutionary biology and are shedding light on a number of phenomena. Here we review some of the major and current fields of research that have greatly contributed to our understanding of the evolutionary dynamics and importance of SRR genes and genetic systems in understanding reproductive biology and speciation. 1. Introduction Science aims to provide simple and general explanations for natural phenomena, and all sciences must deal with the problem of heterogeneity. Variation and heterogeneity are the hallmarks of biological diversity and capture the attention of anyone interested in trying to unravel the mysteries of the biological world. Explaining biological diversity was indeed the problem for which Darwin provided a simple but revolutionary solution [1]. Variation and adaptation are the first two words that come to mind in relation to living organisms, and it was Darwin¡¯s genius that in using these two observations he was able to formulate the theory of natural selection to explain the diversity that we see reflected in the millions of different kinds of organisms or species on this planet. Given its spectacular success in providing a causal explanation for organismic change (evolution within lineages), it is equally remarkable that Darwin was unable to provide a causal mechanism of speciation (evolution between lineages). Such a causal theory had to wait nearly a century after the publication of Darwin¡¯s Origin of Species [1] and it materialized only after the evolutionary synthesis of the 1940s after population genetics had developed a theoretical framework [2, 3]. 2. Speciation Genetics: Mendelian versus Molecular Approach Diversity is a problem in biology in two ways: the most obvious of which is that diversity needs to be explained; the other is that it can thwart %U http://www.hindawi.com/journals/ijeb/2012/191495/