I See You. In Color.
Color vision is something that you, like me, probably take for granted on a daily basis, unless you’re a part of the 8% of men or 0.5% of women that are color blind. Seeing color sets us apart from some other mammals, and places us in a group with a variety of invertebrates, reptiles, birds, and more!
The earliest ancestors of primates, researchers believe, started out with either monochromatic or dichromatic vision. If they had dichromatic vision, they could see in shades of blue and green, whereas if they had monochromatic vision, they would have seen in shades of grey. Somewhere along the line, primates developed the proper equipment for seeing the color red. Grant Allen, a 19th-century biologist teaching in Jamaica, theorized that primates needed color vision to readily identify ripe red and orange fruits (as opposed to inedible, unripe ones) amongst the green leaves of tropical trees.
The thing is, a lot of primates eat more leaves than fruit, and some fruit-eating primates can’t see reds, and some fruits are green when they’re ripe. So Peter Lucas and Nathaniel Dominy of the University of Hong Kong, China, put together a study of primates in Uganda to see if color vision had anything to do with eating just leaves. As it turns out, newer leaves have shades of red in them whereas older leaves are just green. Fresher leaves, according to this article on the study by the BBC, possess more protein and are easier to digest, which means there’s an advantage to seeing red.
Another awesome theory has been developed by some researchers at the University of California. Emily Liman and Hideki Innan found that two phenomena in primate pre-history appeared to have occurred around the same time: the decline of a heightened sense of smell, and the ability to see red. Most mammals have a great sense of smell, but primates – and especially humans – have largely lost the use of it. Liman and Innan conjecture that, because some female primate species have big, red, swellings in their genital areas during estrus, the development of better color vision would have allowed males to tell when females were in heat. With a good sense of smell, males would have been able to smell pheromones put off by the females, but as the ability to smell pheromones declined, it appears that the ability to see reds increased. The same article claims that mammals have more than a thousand genes for olfactory receptors, but that more than 60 percent of those genes are nonfunctional in people! (Imagine what we could be smelling! …or maybe we shouldn’t imagine such things.)
Other critters have color vision, and some can see things we can’t. Bees and birds, for example, can detect ultraviolet light, which humans can’t see. Some, like the helmet gecko, can detect color in dimly-lit situations, something else that humans can’t do. Still others, specifically the mantis shrimp (which is neither a mantis nor a shrimp) may have the most sophisticated vision on the planet: this creature can see colors ranging from infrared to ultraviolet.
Whatever its evolutionary benefit, having color vision is one of the great things about being a human. We’re a fortunate species to have the opportunity to experience a sunset in the smoke of a wildfire, a field of wildflowers, or a stained glass window.
The Color Vision & Art page of WebExhibits.org (if you haven’t been, it’s an amazing site – interactive online museum stuff!) explains that humans may see four basic colors (green, red, blue, yellow), but they work in pairs. Color blindness presents as one of three impairments: the inability to discern blues from yellows (not very common), the inability to discern greens from reds (most common), or just total monochromacy. Please go here and play with the little exhibits. It’s fun. I promise. I’m doing it right now.
Palomar University has this REALLY FREAKING COOL webpage dedicated to color vision in primates that features neato images.
Posted on August 15, 2010, in Biology/Ecology and tagged advantage, blue, color vision, cones, estrus, evolution, green, humans, mantis shrimp, natural selection, naturalist, nature, primates, red, roaming naturalist, rods, sunset, yellow. Bookmark the permalink. 6 Comments.