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By Patricia Reaney
LONDON, Mar 14 (Reuters) - Humans have apes and monkeys to thank for their acute sense of color, scientists in Hong Kong said on Wednesday.
If our primate ancestors had not needed to distinguish red from green to survive--to find tasty ripe fruit and nutritious leaves in forests--humans may not have evolved with the ability to enjoy such a colorful world.
"We humans owe our unique color vision to our primate ancestors," Nathaniel Dominy, of the University of Hong Kong, said in an Internet interview.
Apes and monkeys from Africa and Asia can see vivid reds, greens and blues just like humans in contrast to all other nonprimate mammals. Dominy and his colleague Peter Lucas studied four species of Old World primates in Uganda to find out why.
"Our study is the first to link a nutritional value with primate food colors," said Dominy.
In research reported in the science journal Nature, the scientists monitored the eating habits of primates in the Kibale Forest in Uganda to see how their ability to see colors influenced which fruits or leaves they ate. Distinguishing the healthiest food is essential for primates to survive.
Dominy and Lucas found that apes and monkeys can choose fruit using only yellow/blue vision but the animals had to see red and green to find the most nutritious young leaves which often have a tinge of red that sets them apart from the green forest.
"We found that a primate lacking the ability to discriminate red-green could still detect ripe fruits but not red leaves. There is value to this because young leaves are rich in protein and easier to chew. All primates, even those that eat mostly fruits, have to rely on young leaves during the year when fruits are unavailable," Dominy explained.
But he added that more humans suffer from color blindness than monkeys so we may be losing our ability to distinguish red from green.
Only about three percent of monkeys are red-green color blind compared to eight percent of Caucasian males.
"So it looks like the selective pressure on we humans has been relaxed, perhaps because we have lived outside the forest for some time now," he added.
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