Of two hunky monkeys, which would you say has the most sex appeal?
That’s easier to answer if you’re a rhesus macaque (Macaca mulatta)—or Constance Dubuc, an evolutionary biologist at the University of Cambridge.
Since 2012 Dubuc and colleagues from New York University have studied more than 250 free-ranging rhesus macaques at a field site in the Caribbean. The goal: to learn how face color—which varies from pale pink to deep red in the species—affects reproductive success.
To isolate colour’s role in attraction, Dubuc showed each rhesus test subject two photos of faces in different shades of red. She found that dark red faces appeal strongly to females and somewhat to males—and she did so, in part, by tracking eye movements. “It’s the same as with humans,” she says. “If you see someone attractive in a bar or on the street, your eyes will linger a little longer.”
Researchers also logged the monkeys’ courtship acts by face color—and found that dark red–faced males got more propositions, from more females, than medium- or pale-colored males did.
In the best measure of reproductive success—number of offspring—dark red–faced females outdo paler ones. But for males, there’s a twist: To get more couplings, and thus more offspring, they must have dominance in their group as well as a dark red face, Dubuc says. “Colour alone wouldn’t be enough.”
PHOTOGRAPH BY CONSTANCE DUBUC
HABITAT/RANGE/CONSERVATION STATUS: The nonhuman primates with the biggest geographic range, these monkeys are plentiful and live in varied habitats, chiefly in Asia.
OTHER FACTS: Many bird species sport colours that attract mates; rhesus macaques are one of the few mammal species that do.
Header Image: PHOTOGRAPH BY CONSTANCE DUBUC