BEIJING, March 26 (Xinhuanet) -- American scientists have successfully introduced a human gene into mice that allows the small rodents to see the world in living color.

    The advance helps resolve a long-standing debate about how color vision arose in human ancestors tens of millions of years ago and hints at the possibility of curing some of the millions of colorblind Americans -- and even enhancing the color vision of healthy people with normal eyesight.

    "It opens up huge doors to understanding how color vision evolved and where it can go," said Brian Verrelli, an evolutionary geneticist who studies color vision at Arizona State University and was not involved in the work, published today in the journal Science.

    Most mammals have limited color perception similar to people with red-green colorblindness. Their eyes have two kinds of color detectors, or "cone" cells, each sensitive to a different part of the spectrum.

    Unable to see the difference between reds and greens, they view the world in a mixture of blues and yellows, with gray overlays added by black- and white-registering "rod" cells.

    By contrast, most people -- along with Old World primates and South and Central American female monkeys -- have three kinds of cones that allow them to see the vibrant world of reds and a vast number of related hues.

    Scientists studying the evolution of color vision already had identified the DNA mutation that gave rise to the third kind of cone cell. But they have argued about whether that mutation immediately conferred a new range of color perception or whether generations had to pass before changes in the brain's neural circuitry could take advantage of the novel inputs.

    "This experiment says it had an advantage immediately," said Jeremy Nathans, of the Johns Hopkins Medical School in Baltimore, who led the new study with Gerald Jacobs of the University of California, Santa Barbara. "And if you think about it, that's a very good way to build a brain, so that even a small evolutionary tweak can immediately give you an advantage."

    Biologists theorize the sudden ability to see red was a windfall for primates, allowing them to more easily locate ripe fruit and perhaps picking up signs of good health in potential mates.

    The fact mice never acquired -- or at least never retained -- trichromatic vision suggests it may not be of much evolutionary value to them, perhaps because they are nocturnal.

    (Agencies)