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| Male Broad-tailed hummingbird, Selasphorus platycercus Photo Noah Whiteman University of California-Berkeley |
One of the more idiotic and demonstrably false claims by intelligent [sic] design creationists is that the human eye is so perfectly designed that it must have been intelligently designed by magic. This claim is even hilariously repeated by spectacle-wearing Ken Ham of the disinformation site, Answers in Genesis, blissfully oblivious of the contradiction his vision-correcting spectacles betray.
However, a few minutes studying vision in other vertebrates will show that the human eye is actually fairly ordinary and unremarkable as vertebrate eyes go. It lacks the visual acuity of an eagle's eye for example, and now, as this study shows, we can see (sorry!) our eyes lack the colour vision of birds; in this case a broad-tailed hummingbirds, Selasphorus platycercus.
Humans have three types of cones in their retinas which are able to detect red, green and blue wavelengths in the colour spectrum, but birds have a fourth - able to detect ultraviolet light. This is useful to birds such as hummingbirds because it means they can see the colour combinations in flowers which have co-evolved with insects like bees - which can also detect ultraviolet light.
This range of colour-vision was demonstrated by an ingenious experiment carried out by a group of researchers led by Mary Caswell Stoddard, an assistant professor in the Princeton University Department of Ecology and Evolutionary Biology, and which included scientists from Princeton, the University of British Columbia (UBC), Harvard University, University of Maryland and RMBL. Their findings were published in Proceedings of the National Academy of Sciences (PNAS), a few days ago.
Liz Fuller-Wright of Princeton's Office of Communications explains:
"Most detailed perceptual experiments on birds are performed in the lab, but we risk missing the bigger picture of how birds really use color vision in their daily lives,” Stoddard said. “Hummingbirds are perfect for studying color vision in the wild. These sugar fiends have evolved to respond to flower colors that advertise a nectar reward, so they can learn color associations rapidly and with little training".
Stoddard’s team was particularly interested in “nonspectral” color combinations, which involve hues from widely separated parts of the color spectrum, as opposed to blends of neighboring colors like teal (blue-green) or yellow (green-red). For humans, purple is the clearest example of a nonspectral color. Technically, purple is not in the rainbow: it arises when our blue (short-wave) and red (long-wave) cones are stimulated, but not green (medium-wave) cones.
While humans have just one nonspectral color — purple, birds can theoretically see up to five: purple, ultraviolet+red, ultraviolet+green, ultraviolet+yellow and ultraviolet+purple.
Stoddard and her colleagues designed a series of experiments to test whether hummingbirds can see these nonspectral colors. Their results appear June 15 in the Proceedings of the National Academy of Sciences.
A hummingbird hovers near a flower
To other birds, this male’s magenta throat feathers likely appear as an ultraviolet+purple combination color.
Photo by David Inouye,
University of Maryland-College Park
The research team, which included scientists from Princeton, the University of British Columbia (UBC), Harvard University, University of Maryland and RMBL, performed outdoor experiments each summer for three years. First they built a pair of custom “bird vision” LED tubes programmed to display a broad range of colors, including nonspectral colors like ultraviolet+green. Next they performed experiments in an alpine meadow frequently visited by local broad-tailed hummingbirds, which breed at the high-altitude site.
Each morning, the researchers rose before dawn and set up two feeders: one containing sugar water and the other plain water. Beside each feeder, they placed an LED tube. The tube beside the sugar water emitted one color, while the one next to the plain water emitted a different color. The researchers periodically swapped the positions of the rewarding and unrewarding tubes, so the birds could not simply use location to pinpoint a sweet treat. They also performed control experiments to ensure that the tiny birds were not using smell or another inadvertent cue to find the reward. Over the course of several hours, wild hummingbirds learned to visit the rewarding color. Using this setup, the researchers recorded over 6,000 feeder visits in a series of 19 experiments.
The experiments revealed that hummingbirds can see a variety of nonspectral colors, including purple, ultraviolet+green, ultraviolet+red and ultraviolet+yellow. For example, hummingbirds readily distinguished ultraviolet+green from pure ultraviolet or pure green, and they discriminated between two different mixtures of ultraviolet+red light — one redder, one less so.
To an intelligent [sic] design creationists, with their touching obsession that a magic designer made them perfectly, at the pinnacle of creation, these revelations are a problem as they show clearly that the human eye is far from the example of perfection they claim, and which it would be if designed by a perfect designer who wanted the best for his favourite creation.
To an evolutionary biologist, this is easy to explain. As mentioned above, birds, especially these hummingbirds, which have the same need to identify flowers containing nectar as do bees, having the ability to take advantage of a mechanism which originally co-evolved between bees and flowering plants is patently obvious. There was a clear evolutionary advantage to it.
For humans, however, who have inherited colour vision from a remote simian ancestor which re-evolved the colour vision lost by an even more remote common nocturnal ancestor from the days of dinosaurs. This came about due to flowering plants producing berries for birds as a seed-disposal mechanism and signalling that they were ripe by changing from green to red. Colour-blind mammals were unable to tell the difference but an arboreal monkey would be at a distinct advantage if it could understand this same signalling mechanism. The result is that humans, like all the descendants of that early fructivorous simian, have the ability to tell red from green, but anything more would not have given any advantage. For a detailed explanation of this see Lessons From Nature.
Imagine the mental gymnastics and denialism needed to try to force-fit this into an 'intelligent [sic] design model which has ended up with a suboptimal human eye when better 'designs' exist in nature. Tweet
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