What Birds See [evolution of the eye]

Scientific American ^ | July 2006 | Timothy H. Goldsmith

[doc30]

We humans customarily assume that our visual system sits atop a pinnacle of evolutionary success. It enables us to appreciate space in three dimensions, to detect objects from a distance and to move about safely. We are exquisitely able to recognize other individuals and to read their emotions from mere glimpses of their faces. In fact, we are such visual animals that we have difficulty imagining the sensory worlds of creatures whose capacities extend to other realms--a night-hunting bat, for example, that finds small insects by listening to the echoes of its own high-pitched call. Our knowledge of color vision is, quite naturally, based primarily on what humans see: researchers can easily perform experiments on cooperative human subjects to discover, say, what mixtures of colors look the same or different. Although scientists have obtained supporting information from a variety of other species by recording the firing of neurons, we remained unaware until the early 1970s that many vertebrates, mostly animals other than mammals, see colors in a part of the spectrum that is invisible to humans: the near ultraviolet. ...

[doc30]

Essentially, the article says that fish, reptiles, amphibians and birds all evolved the capacity to see in the UV in the form of tetrachromic vision. Mammals were once that way, too. But during the time of the dinosaurs, mammals became nocturnal and lost two of the four receptors but gained better light sensitivity for nocturnal vision. Hence, all mammals are dichromatic. A certain lineage of primates experienced a mutation that shifted slightly one of the color receptors and evolved a weak version of trichromatic vision. Humans are part of that lineage. So, for those that say the eye could not have evolved because it is too complicated, be aware that it has now been shown that our eyes have de-evolved from non-mammilian vertebrates. They became much less 'complex' then genetic changes re-evolved some lost features. It sahows evolution works in both 'directions.'

One of my favorite examples from the article was about how birds of prey, kestrels in particular can see UV. Rodents leave urine-based scent trails, but urine has a 'UV color' that these birds can see. If you were a kestrel, you could see lines of urine trails zig-zagging across the coutryside and follow a trail to find your lunch. Also, birds without sexual dimorphism (i.e. you can't tell male from female visually) actually do have sexually dimorphic coloration in the UV. Other birds can see it but we can't.

[doc30]

ping

[Central Scrutiniser]

[GSlob]

Thanks for the smile.

[RadioAstronomer]

Thanks for the post. Interesting read.

[conservativefreak]

The cartoon was funny, however, it oversimplifies what a creationists means when s/he says that they don't believe in evolution they mean that they don't believe that random mutations can add complexity to an organism that didn't already have it in it's genetic code, and that successive generations of bacteria won't mutate into a frog, no matter how many generations you have.

[PatrickHenry]

Evolution Ping The List-O-Links

A conservative, pro-evolution science list, now with over 380 names. See the list's explanation, then FReepmail to be added or dropped. To assist beginners: But it's "just a theory", Evo-Troll's Toolkit, and How to argue against a scientific theory.

[Mike Darancette]

If you were a kestrel, you could see lines of urine trails zig-zagging across the coutryside and follow a trail to find your lunch.

I wonder if the nocturnal Owls have the ability to see in the UV?

[jagusafr]

...if you believe in that sort of thing...

[sully777]

Ouch.

[Windsong]

You do know that this is a Conservative site, right?

[hometoroost]

If one is making one's point with a Gary Trudeau cartoon they should begin to question if they understand the issue at all. It's not surprising that they wouldn't understand the creationist point of view.

Liberals always simplify and label things they disagree with because it's easier than thinking. Trudeau is the poster boy for that type of argument.

[Kenny Bunkport]

I agree with your comment, except the part where you said the cartoon was funny.

[Billthedrill]

Five posts until some horse's patoot turns this article into an opportunity for another infantile crevo pissing contest. Counting down...

[djf]

There was a show about bird vision on Discovery a few years back.

At the very back of the retina, birds have this sort of "dimple" formation, packed with visual receptors.

The net result is that for the peripheral vision of birds, everything is seen as normal. But for a small circular section in the center of their field of vision, everything is magnified. So if they look straight at something, they "zoom in" on it.

[villagerjoel]

I saw that comic yesterday and thought to myself that it was a poor argument. The point should have been, "Do you want me to treat you for TB, or the AIDs that it evolved into." MY point is that it is the same thing. TB is TB, with variation, and I don't think many of those who don't believe evolution to be fact are arguing that organisms don't adapt and change. The point is TB doesn't be come Aids, or plankton, or a cow.

[pgyanke]

Five posts until some horse's patoot turns this article into an opportunity for another infantile crevo pissing contest.

Why not? It only took 14 for someone to throw a stream...

[Sentis]

You know that a person can believe in evolution, in God, and in Jesus and still be conservative. Oh my god a Bhuddist or a Hindu could be conservatives also and have a completely different set of creation beliefs. Hey I had a thought I think even an atheist could be a conservative.

[Kenny Bunkport]

To use a Trudeau cartoon to make a point, it's evident that this whole discussion about Darwinism on FR has less to do with science, and more to do with a philosophical agenda.

[BaBaStooey]

Its such a shock that we are at the top of the food chain despite being "de-evolved."