A new study suggests that primates' ability to see in three colors may not have evolved as a result of daytime living, as has long been thought.
The findings, published in the journal Proceedings of the Royal Society B, are based on a genetic examination of tarsiers, the nocturnal, saucer-eyed primates that long ago branched off from monkeys, apes and humans.
By analyzing the genes that encode photopigments in the eyes of modern tarsiers, the researchers concluded that the last ancestor that all tarsiers had in common had highly acute three-color vision, much like that of modern-day primates.
Such vision would normally indicate a daytime lifestyle. But fossils show that the tarsier ancestor was also nocturnal, strongly suggesting that the ability to see in three colors somehow predated the shift to daytime living.
The coexistence of the two normally incompatible traits suggests that primates were able to function during twilight or bright moonlight for a time before making the transition to a fully diurnal existence.
"Today there is no mammal we know of that has trichromatic vision that lives during night," said an author of the study, Nathaniel J. Dominy, associate professor of anthropology at Dartmouth. "And if there's a pattern that exists today, the safest thing to do is assume the same pattern existed in the past.
"We think that tarsiers may have been active under relatively bright light conditions at dark times of the day," he added. "Very bright moonlight is bright enough for your cones to operate."
This article originally appeared in The New York Times.