While he was still in graduate school, psychologist Frank Muscarella started thinking about male pattern baldness.
Muscarella wasn't worried about his own hair, which was thick and dark. He wondered why a small percentage of men start to lose their hair in puberty and are pretty much completely bald by the time they're adults.
The answer, he suspected, had something to do with evolution.
Until perhaps the 1950s, most scientists who thought about the problem would probably have said that baldness was a medical problem, like bad breath or cancer. The notion that it served some purpose - that evolution had made some men bald - might have seemed absurd.
But then, a new generation of Darwin's disciples began to rethink his theories in the light of the emerging science of genetics, and to use both ideas to study traits - everything from aggression and creativity to body odor and baldness - and how they might be related to human behavior and society.
Today, the very idea of evolution is under assault from creationists, or others who think life is the product of "intelligent design." But supporters of evolution are themselves engaged in a fierce debate over Darwin's theory that could have profound implications for the way we think about ourselves and our world.
Almost a century and a half after Darwin first published his ideas, scientists are bitterly split over whether the theory can be applied far beyond the worlds of fossils and museums, into the realms of psychology, economics, art, literature and even religion.
Take baldness, for example. Muscarella and a colleague, Michael R. Cunningham, suspected that evolution could help explain it. So they showed pictures of men with a lot of hair, men with a little hair and men with no hair to a group of women and asked them to describe what they saw.
Although the women found the bald men less attractive, they also described them with words like "nonthreatening," "intelligent," "influential" and "approachable."
Muscarella and Cunningham theorized in a 1996 paper in the journal Ethology and Sociobiology that the first men who suffered male pattern baldness appeared older and wiser than their years. "Think of how priests shave their heads, about how we talk about the egg-headed professor," said Muscarella, a professor at Barry University in Florida, in a phone interview.
This apparent sagaciousness could have enhanced what scientists call "fitness," the ability of bald men to survive and reproduce. It may have helped males compete for the affection of women, and that would have helped them have children - and pass on their baldness genes to their descendants.
Muscarella's effort was widely reported in the press. But it was also lampooned by the satirical Annals of Improbable Research. And it was derided by the prominent primate researcher Frans B.M. de Waal, who in 2001 told the Monitor on Psychology that just because baldness may have a genetic base doesn't mean it was a product of evolution. "Alzheimer's is genetically based," de Waal wrote. "It doesn't contribute to fitness."
"He implied that it was not well thought out, that it was silly," Muscarella recalled. But that hasn't stopped him from continuing his efforts to study the possible evolutionary roots of other human traits, including homosexuality. Nor has it shaken his faith in his theory that baldness is an evolved trait. "It's stupid that more hasn't been done," he said.
Over the past decade, there has been an explosion of research like Muscarella's into the potential evolutionary roots of a wide range of things - monogamy, murder, eating disorders and the preference of certain European populations for blond hair and blue eyes. Scholars and writers have hunted for the influence of Darwin's theory in the workings of modern corporations, in the fluctuations of the stock market and even the plots of Jane Austen novels.
And despite years of research and debate, the potential intersection of evolution and human behavior remains politically explosive. When Harvard President Lawrence H. Summers 14 months ago mentioned offhand a theory that women may lack men's "intrinsic aptitude" for science, he was merely saying what evolutionary psychologists have been arguing since at least the early 1990s.
That comment provoked outrage on campuses around the country and led to Summers' censure by Harvard's faculty in March 2005. Under pressure from critics, Summers resigned last month.
His treatment angered some leading evolutionary psychologists, who say their work is under attack on college campuses in the name of political correctness.