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Explaining the mysterious and sometimes perplexing differences between males and females would seem to be beyond even the province of as exacting a discipline as science.

But recent research from the laboratory of Sean Carroll, a UW-Madison molecular biologist, has at least shed light on what happens at the genetic level to make males and females of any species look so different.

Though the work was done by studying markings on fruit flies, the same genetic mechanism is likely responsible for the male moose having big antlers, male lions having impressive manes, and male peacocks having those long and showy tail feathers. In humans, the process could help explain how men end up being larger than women. And hairier.

Such traits are called secondary sexual characteristics — traits other than reproductive organs that are specific to one gender or another. They were the basis for Charles Darwin's theory of sexual selection, the idea that such elaborate and showy characteristics are an advantage when it comes to finding a mate.

The work is published in the latest edition of the journal Cell.

By studying, manipulating and comparing generations of fruit flies over more than seven years, Carroll and his team of researchers zeroed in on the workings of the genetic circuit responsible for making males and females different.

"Males and females basically have the same set of genes,'' said Thomas Williams, a UW-Madison post-doctoral fellow who helped lead the study. "So how do you specifically modify the activity of a male's genes but not a female's genes?''

It turns out that such a seemingly important task is performed by a simple switch that determines whether a gene makes a particular protein available. The researchers discovered this by studying ornamentation on the male fruit fly's abdomen. Though the same set of genes studied existed in both the male and female fruit flies, the gene in males repressed the production of a protein. Without that protein, the males ended up sporting a more colorful rear end than females.

The finding adds to much of the other evolutionary science coming from Carroll's lab and the broader idea that evolution works with a surprisingly small suite of genes to create big differences. It is one of the wonders of the evolutionary process, Carroll said, that such major differences as the male lion's mane or the male peacock's tail can be prompted by such a subtle change at a very specific location in the genome.

Interestingly, though Darwin's theories lead most people to believe that such changes are driven by natural selection, science has not actually proven the role of the peacock's tail or any other such showy traits in making it easier to attract mates.

And Carroll is very careful to point out that this latest science is about how such differences arise and not why. But, Carroll added, the research may spur behavioral experiments that help prove such a connection.

Evolutionary biologists are certainly intrigued by the question because of the presence of so many exaggerated secondary sexual traits in all species, from elephant seals to beetles.

"These are the most rapidly evolving traits in evolution," Carroll said. "If female tastes change, these traits go away. There is no reinforcement. ... As long as the gain outweighs the cost, the feature will survive."