It drives advertising and launches wars, and now a Canadian population
biologist says scientists have seriously underestimated a central force in the origin of new species – sex.

According to McMaster's Rama Singh, new evidence is revealing that sex and reproduction-related genes are the overlooked supercharged engines for the evolution of new types of animals and plants.

“Most species live in a stable environment, and therefore in my mind, the force of natural selection is smaller than sexual selection. This is because sexual selection involves two components – males and females – and they always have to adjust to changes in the other sex regardless of whether those changes are due to selection or chance,” says Singh, a biology professor at McMaster University. A species is any group of animals or plants that can interbreed and produce fertile
offspring.

Since Charles Darwin and Alfred Wallace championed the modern scientific theory of evolution in the mid-1800s, the emphasis in explaining the process has been natural selection. This is the biological dance between generations of a species and its environment which leads to the “survival of the fittest”, and the gradual evolution of new species. The dance of reproduction within a population, or sexual selection, has generally been seen as a smaller component of natural selection.

But based on new DNA and other molecular evidence, Singh and others believe that sexual selection might well be the missing link to better explain what has separated mice from men.

Singh recently took advantage of breakthroughs in mapping the genomes of mice and humans to conduct a broad comparison of the two species' genes. He found that there's a much greater level of difference in the sex and reproduction-related genes between them than in those linked primarily to growth and development.

“The group of genes that show the greatest divergence between mice and men are the sperm genes, those that code for proteins in the sperm,” says Singh. “These genes are not only highly diverged in their DNA sequence, but they are also more diverse in the length of the coding region.” The findings will appear in the November issue of the scientific journal Molecular Biology and Evolution.

In the late 1960s, new molecular analysis technology led to a boom in
studies exploring the molecular level differences between species. But these studies ran into a quandary. Distantly related species showed significant differences in their proteins (the molecules coded for by DNA). But for species believed to have diverged recently (for biologists that's less than two million years ago) there was little genetic difference between these species that could be related to their level of reproductive isolation.

“We began to think that if we're interested in speciation, why should we be looking at all the genes in the genome? We should be looking at the genes that are more likely to be affected. So we focused on proteins which are found in the testis and ovaries,” recalls Singh.

This new line of research, begun with fruit flies in 1985, demonstrated that these fertility-related proteins are in fact the most diverse group of proteins between species of fruit flies.

Now Singh's research is trying to corroborate the mounting evidence
that, in general, sex and reproduction-related genes also mutate and evolve more quickly than genes related to growth and development.

The research has far reaching implications, including offering what Singh calls “a new paradigm for the conceptual unification of various
theories of speciation into one.”

It could also heavily influence how paleontologists interpret the appearance of new species in the fossil record. Singh points out that the fossil record doesn't preserve such key sexual selection characteristics as mating behaviour and genitalia.

As a result, he says: “What paleontologists call the appearance of a new species based on changes in the hard parts they find-the bones, teeth and shells-is actually long after it's already become a distinct species.”

(From the Natural Sciences and Engineering Research Council of Canada News Bureau Bulletin)