Red can symbolize danger, heat and even anger.
It's true: The color's appearance in road signs, stoplights, labels and flushed cheeks often cautions humans to avoid harm.
One study even found that Olympic competitors donning red uniforms were more successful at winning events, suggesting the color intimidates the competition.
And a recent set of experiments featured in the journal Psychological Science indicates humans' apprehension of red may have evolutionary roots, leading to greater consideration of the color's use in human sports and primate habitats.
In the study, Dartmouth College researchers measured reactions from rhesus macaque monkeys when they were given the option to take food from human testers. The species was studied because these primates have similar visual capabilities as humans and use redness as an expressive form of communication - just like people blush or redden when aroused or angry.
Scientists set up several experiments allowing the monkeys to "steal" food from human testers, each of whom dressed in a different color T-shirt and baseball cap - either red, green or blue. Researchers predicted the monkeys would avoid stealing from the tester wearing red, and they were right.
Monkeys preferred testers wearing green or blue and avoided those dressed in red, regardless of the tester's sex. The team says the monkeys' submissive actions suggest our avoidance of red may have evolved in humans' last common ancestor with Old World monkeys.
But the research isn't without caveats. For starters, the experiments were only performed among male monkeys, making it difficult to generalize. Also, drawing conclusions from experiments in which animals react to individuals outside their own species may confound results.
Though the conclusions confirm primates' avoidance of red, what drives our hesitation around the color is still unknown. It's possible that aversion to red evolved more than once across primate species, including humans.
It also could have given early humans and other nonhuman primates the benefit of distinguishing ripeness and toxicity in foods such as fruits and plants. And as evident from humans' tendency to turn red when angry, aroused or upset, such color recognition assists visual communication, too.
But before suggesting sports organizations ban red in athletic apparel - as the authors write - it seems more research is needed to confirm the color's negative effects on athletic performance.
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