You can tell a lot about the personality of a bighorn sheep by trying to wrestle one to the ground.
The aggressive animals, like the ram nicknamed Psycho, put up a fight every time. The docile ones never require a half-nelson: They freeze as soon as they are touched and calmly sit down.
Researchers who trap, weigh and measure the bighorn sheep every summer in the mountains near Nordegg, Alta., have been kicked and dragged by the more combative beasts. The scientists are taking part in a Ram Mountain trap-and-release study, started in 1972, that has provided crucial data about the growth and health of the bighorn sheep population. In recent years, the study has also offered Canadian biologists a remarkable opportunity to investigate personality differences in the 125-kilogram animals.
Not many researchers study personalities in wild animals, a field that until relatively recently was dismissed by critics as a foolish attempt to attribute human characteristics to other creatures. But since the early 1990s, biologists have demonstrated that hyenas, chimps, squirrels, birds, octopuses, fish and spiders have measurable personality differences. They can be shy or bold, aggressive or passive, loners or social.
A number of studies - including a recent paper on the Ram Mountain bighorn sheep - have demonstrated that these traits have a strong genetic component.
In their study in the Journal of Evolutionary Biology, researchers from the University of Sherbrooke and the University of Alberta report that more aggressive rams and ewes tended to have offspring that were also fighters. The more docile ones had lambs that were more likely to grow up to be easygoing.
Now, they are looking for genes linked to those traits. If they are successful, their work could explain behaviour in other species too.
"The question is: Are the same genes that are influencing behaviour in sheep in humans?" Jocelyn Poissant says. A doctoral student, he spent three summers wrestling sheep. This year, however, he stayed in the lab to analyze their DNA. It was easier on his knees.
"They kick. Sometimes they will drag you for four metres, and your knees are all scratched."
The animals are lured into the corral trap with salt, and even those that put up a fierce struggle relax once a blindfold is slipped over their eyes. "They calm down and it's safe for everybody," Mr. Poissant says.
While the field of research offers the possibility of learning more about the evolution of personality in humans, it could also prove increasingly important as conservationists work to protect species that are in trouble, says David Coltman, the head of the wildlife genetics lab at the University of Alberta.
Personality traits such as boldness are often linked to other important characteristics such as size and faster reproductive rates, says Peter Biro, a Canadian biologist working in Australia.
"It would be hard to be fast-growing and reproducing if you were sitting there scared behind a rock," he says.
But being bold can be dangerous in some circumstances, Dr. Biro says. He stocked one lake in British Columbia with shy rainbow trout and another with bold ones. Over five days of gillnet fishing, three times more bold fish were caught.
This could explain why the northern cod are not rebounding in the waters off Newfoundland, he says. Perhaps most of the bold, fast-growing fish were harvested, leaving only the slower-growing, shy fish to breed.
"They tend not to school so much," says Dr. Biro, who takes up a position at the University of Alberta next month.
Dr. Coltman says anyone who has bred animals will not be surprised by findings that personality traits are genetic, although it has been only recently that there has been strong evidence to prove that this is the case.
Frans de Waal, a primatologist in Atlanta whose latest book is about the evolution of empathy in mammals, says scientists tend to underestimate animals, especially compared with non-scientists who work and live with them.
In The Age of Empathy , Dr. de Waal writes about a female elephant that acted as a guide for a blind, but unrelated female, and marshals a wide range of evidence to support the idea that the mammalian brain is hard-wired for empathy.
Studying animals can offer insight into the evolutionary roots of emotion and personality in humans, he and other researchers contend. Sometimes, however, that means sacrificing a little skin.
Mr. Poissant never encountered Psycho, Ram Mountain's legendary fighter, which was killed by a poacher. But he handled the female equivalent, the ewe known as Green Stripes because of her identifying ear tag.
"On a scale of seven, she always ranked seven. It is just hard being dragged on the ground. The bottom of the trap is mud and rocks."
Anne McIlroy is The Globe and Mail's science reporter.