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Monkeys stop on red, too

June 9, 2011
Courtesy of the Association for Psychological Science
and World Science staff

Al­most un­iver­sally, red means stop. Red means dan­ger. Red means hot. And an­a­lyz­ing the re­sults in the 2004 Olympics, re­search­ers have found that red al­so means dom­i­nance. Ath­letes wear­ing red pre­vailed more of­ten than those wear­ing blue, es­pe­cially in hand-to-hand sports like wres­tling.

Rhesus macaques (im­age cour­tesy D. Ma­es­tri­pieri, U. of Chi­ca­go; home­page im­age cour­tesy of Lau­rie San­tos, Yale U.)


Why? Is it ran­dom? Is it cul­tur­al? Or does it have ev­o­lu­tion­ary roots? A new study in­di­cates some male mon­keys al­so back off in the pres­ence of red, sug­gest­ing the ten­den­cy is a prod­uct of ev­o­lu­tion, re­search­ers say. Mon­keys are rel­a­tives of the dis­tant an­ces­tors of hu­mans.

“The si­m­i­lar­ity of our re­sults with those in hu­mans sug­gests that avoid­ing red or act­ing sub­mis­sively in its pres­ence may stem from an in­her­it­ed psy­cho­log­i­cal pre­dis­po­si­tion,” said neu­ro­sci­ent­ist Jer­ald D. Kra­lik of Dart­mouth Col­lege in New Hamp­shire, one of the in­ves­ti­ga­tors. The find­ings are to be pub­lished in an up­com­ing is­sue of the jour­nal Psy­cho­log­i­cal Sci­ence.

Two hu­man ex­pe­ri­menters, one male and one fema­le, en­tered a col­o­ny of free-rang­ing  rhe­sus macaque mon­keys in Cayo Santi­ago, Puerto Rico and ap­proached iso­lat­ed males. Both peo­ple knelt down, put a Sty­ro­foam tray in front of them, drew an ap­ple slice from their back­packs, held the slice at chest lev­el for the mon­key to see, then placed the ap­ple on the trays. Both stood up sim­ul­ta­ne­ously and took two steps back.

The mon­key typ­ic­ally went di­rectly to the slice he wanted, grabbed it and ran off.

The hu­mans wore T-shirts and caps, whose col­ors—red, green, and blue—were changed in each of four con­di­tions: red on fema­le, green on ma­le; then vice-versa; red ver­sus blue; blue ver­sus green.

The mon­keys paid no mind to the sex of the ex­pe­ri­menter. Green or blue made lit­tle dif­fer­ence to them ei­ther. But in the sig­nif­i­cant ma­jor­ity of cases, they steered clear of the red-clad hu­mans and stole the food from the oth­er tray, the sci­ent­ists said.

“We – pri­ma­tes and then hu­mans – are very vi­su­al,” Kra­lik ex­plains. “We are al­so very so­cial.” In both realms, col­or has im­por­tant ef­fects, from tell­ing us which food is ed­i­ble to help­ing us gauge the emo­tions of oth­ers by the rel­a­tive red­ness of their skin. Put the two to­geth­er, he said, “and we start to see that col­or may have a deeper and wider-rang­ing in­flu­ence on us than we have pre­vi­ously thought.”


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Almost universally, red means stop. Red means danger. Red means hot. And analyzing the results in the 2004 Olympics, researchers have found that red also means dominance. Athletes wearing red prevailed more often than those wearing blue, especially in hand-to-hand sports like wrestling. Why? Is it random? Is it cultural? Or does it have evolutionary roots? A new study indicates some monkeys also back off in the presence of red, suggesting the tendency is a product of evolution, researchers say. “The similarity of our results with those in humans suggests that avoiding red or acting submissively in its presence may stem from an inherited psychological predisposition,” said neuroscientist Jerald D. Kralik of Dartmouth College in New Hampshire, one of the investigators. The findings are to be published in an upcoming issue of the journal Psychological Science. The study involved male rhesus macaques, a species of monkeys that is sensitive to red, green, and blue, ranging freely in Cayo Santiago, Puerto Rico. Two human experimenters, one male and one female, entered the monkeys’ colony and found isolated males to test. Both people knelt down, put a Styrofoam tray in front of them, drew an apple slice from their backpacks, held the slice at chest level for the monkey to see, then placed the apple on the trays. Both stood up simultaneously and took two steps back. The monkey typically went directly to the slice he wanted, grabbed it and ran off. The humans wore T-shirts and caps, whose colors—red, green, and blue—were changed in each of four conditions: red on female, green on male; then vice-versa; red versus blue; blue versus green. The monkeys paid no mind to the sex of the experimenter. Green or blue made little difference to them either. But in the significant majority of cases, they steered clear of the red-clad humans and stole the food from the other tray, the scientists said. So it’s It’s no accident, they added, that humans know that red means no. “We – primates and then humans – are very visual,” Kralik explains. “We are also very social.” In both realms, color has important effects, from telling us which food is edible to helping us gauge the emotions of others by the relative redness of their skin. Put the two together, he said, “and we start to see that color may have a deeper and wider-ranging influence on us than we have previously thought.” While we learn what those influences are, the researchers warn the organizers of competitive activities, such as sporting events and even academic exams, to avoid using color “in ways that may unfairly influence people,” said Kralik.