The researchers observed six hyrax social groups in Ein Gedi, Israel. The groups consisted of adult females, adult males, pups and a group of male bachelors that slept in separate burrows.
Some older males ranked among the most dominant members — below a female or two — but younger males were among the lowest-ranked.
Hair and blood tests revealed females had as much or more testosterone than males.
To eliminate the possibility they were observing an isolated phenomenon, the researchers studied other hyraxes from zoos around Israel and another group in the northern part of the country. The analysis yielded similar results.
Males are the dominant sex in most mammal species, but among rock hyraxes, low-ranked bachelors can often be seen sitting alone or huddling with females. Although female hyraxes are no larger than males, they are more likely to fight.
Previous studies suggest testosterone promotes dominance and aggression in human males, with levels rising in men during a challenge. Winners' testosterone levels rise after a fight, while losers experience a testosterone decline.
Research led by James Dabbs, a professor of psychology at Georgia State University in Atlanta, further supports the apparent testosterone-dominance connection.
Dabbs and his team measured the hormone levels of female prison inmates. Women who had committed violent crimes and those who demonstrated "aggressive dominance" in prison had higher than normal testosterone levels.
Neither Dabbs nor Koren, however, are sure which comes first — the violent behavior or the testosterone. Aggression, whether evolved at the species level or developed over an individual's lifetime, may precede the body's release of the hormone.
"It's like the chicken and the egg," concluded Koren, "but hormones come to serve behavior, I think, and not the opposite."
Name: Rock Hyrax (
Procavia capensis)
Primary Classification: Hyracoidea (Hyraxes)
Location: The Middle East, East Africa and most of sub-Saharan Africa.
Habitat: Dry savannah to dense rain forest. Lives in crevices in rocky outcroppings.
Diet: Grasses, leaves, herbs, fruit, insects, lizards and birds' eggs.
Size: Averages 5-9 lbs in weight.
Description: Yellowish or grayish-brown coat; dorsal spot covered with black or yellow hair; rounded head; blunt nose; short, rounded ears; no tail; stumpy toes — four on each front foot and three on the back; hoof-like nails; rubbery soles.
Cool Facts: It shares a common ancestor with sea cows (dugongs and manatees) and elephants. In the past, some hyraxes were the size of oxen, which would explain their unusually long gestation period for a mammal of their size (7-8 months).
Conservation Status: Common
