Colour blindness more common than in the past

LONDON - Humans have apes and monkeys to thank for their acute sense of colour, scientists in Hong Kong say.

And if you are colour blind, it might be because we have been out of the forest too long.

Had our primate ancestors 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 colourful world.

"We humans owe our unique colour vision to our primate ancestors," Nathaniel Dominy, of the University of Hong Kong, said.

Apes and monkeys from Africa and Asia can see vivid reds, greens and blues just like humans, unlike all other non-primate 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 colours," 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 colours 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 red tinge.

"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.

He added that more humans suffered from colour blindness than monkeys, so we may be losing our ability to distinguish red from green.

Only about 3 per cent of monkeys are red-green colour blind compared to eight per cent 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."

- REUTERS