Why do humans see colour? Every other creature seems to have eyes that have evolved to what they need them to be. So.....why do we see such a (relatively) wide range of colours? What do we need these colours for? I'm thinking maybe it's because we ate berries so long ago as a prime food source. But still, would we need as wide a range as we have?
It has been suggested that wolves can see partially into the infrared. That eagle has distance vision supreme. That owl have outstanding night vision. Each adapted to its need. Humans seem to have a general ability. To notice movement, to see color, adequate peripherals vision, and fair depth perception. Not outstanding in any one category but covering a broad range. It is one of the characteristics that give us the adaptability to do a wide range of tasks. From seeing fine detail to general overall scans of terrain we do nothing extremely well but all fair. It suits us, as we need a wide range in tool making and using. Color has its advantages too and I would suspect that you are close to the original reason for it. In nature, a lot of animals have distinct colors, some of which are either deadly or capable of making one sick. Berries that mark themselves by color, once again some deadly, others rather good. Color perception would go a long way towards identifying, which is which.
Finally a thread that really belongs in the Human Science section and it ends up here... *sigh*oh well. Tyler, It is indeed a very tricky question that has been bothering ecological psychologists and, to a lesser degeree, cognitive psychologist. There are quite some philosophical and theoretical problems sticking to the most obvious answers. Still one may think it is most probable that colour vision has the eveolutiory advantage of telling good from rotten food (in case one has a cold and smell is impairedPlease Register or Log in to view the hidden image!). here some links to (links to) papers on the subject: http://cogprints.soton.ac.uk/view-phil-mind.html http://twinearth.wustl.edu/~pp/pp/12_2.html .. just use google to find more
Cones are the structures that allow humans and other mammals to see the colors of the visible spectrum. For example, having fewer cones and more rods in the eye would not allow us to see more colors but would allow us to have better night vision, like a cat. Therefore, the eye cannot see a full array of colors and have good night vision due to the amount of rods and cones in the eye. Color blindness is simply a failure of a particular cone. It is believed that the number of rods and cones in an animals eye is often related to the animals instincts and habits. Nocturnal animals have developed eyes with more rods and less cones allowing them to have better night vision. Hawks have more cones than rods (much more than humans) that allow them to see their prey from long distances.
Q, is there a subject you can't discuss intelligently? I have a question: How can we tell whether or not another animal sees in color?
Q, is there a subject you can't discuss intelligently? Yes. You only need one guess to that answer. Please Register or Log in to view the hidden image! I have a question: How can we tell whether or not another animal sees in color? Although vision is a very complicated process, the difference as to whether an animal will see color or not is dependent on the pigment type (red, green, blue) and amount of cones in the retina. It is only the cones that allow the eye to see colors. Many animals have no cones in their retinas, therefore they do not see colors. If you ever get a chance to see the guns or cannons of a projector, like the older ones that hung on the ceilings of bars and pubs which projected images on a screen, you'll notice there are three of them, red, green and blue.
Xev Of course. We are seeing less of him lately, aren't we? Actually it's not a person, it's a state of mind. Please Register or Log in to view the hidden image!
(Q), Yes we all know how we can see colour. But WHY do we see colour? That is a totally differnt question. And it is the question at hand. (Tyler wrote:"So.....why do we see such a (relatively) wide range of colours? What do we need these colours for?") Besides, your story may give the impression that more cones in the retina will lead to more colours that can be seen. That is of course not true. The detection limit will only be lower. I am not sure that birds of prey have sharper eye vision for the reason of having more cones. Actually cones are larger than rods and therfore one would expect sharper eye vision with more rods, not with more cones!
Q: Oooh! I guessed wrong....hmmmm. An emotion....a specific emotion...that cannot be discussed intelligently or rationally.... Ah! 'Tis love, the consoler of mankind, the preserver of the universe, the soul of all gentle creatures, gentle love. Did I guess right? Melijn: I presume that, since our ancestors ate a lot of fruit and berries and vegetables, we needed color vision to distinguish between poisionous and safe, ripe and un-ripe, etc. As Tyler hypothesized. Also, could color vision have helped us hunt? And can chimps see our range of colors?
(Q), Yes we all know how we can see colour. But WHY do we see colour? That is a totally differnt question. And it is the question at hand. (Tyler wrote:"So.....why do we see such a (relatively) wide range of colours? What do we need these colours for?") I thought I answered that. But one could also ask why do we need our senses at all, why do we need arms and legs, why aren't we just sacks of meat. One could pressume it is simply linked to our survival. I wouldn't want to speculate. Besides, your story may give the impression that more cones in the retina will lead to more colours that can be seen. That is of course not true. The detection limit will only be lower. I am not sure that birds of prey have sharper eye vision for the reason of having more cones. Actually cones are larger than rods and therfore one would expect sharper eye vision with more rods, not with more cones! I don't think so. Rods are actually larger than cones. Rods are sensitive to light, not color. Most retinas have a larger number of rods compared to cones. However, the more cones a retina has, the more sensitive it is to color, not light. Therefore, if a retina has more cones, it has the ability to see colors better than a retina with less cones, as in the example of the hawk.
sorry (Q), Norally I really respect your posts, but now you are wrong. This happenes to be my field of study. As Eric Cartman so strongly put it: "RESPECT MY AUTHORATAH!" Cones are larger than rods. here you have it: Please Register or Log in to view the hidden image! And "evolution made us so" is not an answer to WHY. I thought this forum was for a large part about speculation. Please Register or Log in to view the hidden image!
sorry (Q), Norally I really respect your posts, but now you are wrong. I looked it up. You're right. Cone size: 1-4 micrometers diameter X 50-80 micrometer length. Rod size: 1 micrometer diameter X 60 micrometer length. Good on ya, I stand corrected. As Eric Cartman so strongly put it: "RESPECT MY AUTHORATAH!" Okie Dokie. Who's Eric Cartman? And "evolution made us so" is not an answer to WHY. I said we could presume it is linked to our survival. There really is no concrete evidence as to why, unless you can produce evidence. I thought this forum was for a large part about speculation. Perhaps for others. I don't like to speculate without evidence.
never mind all that. My guess is that in very keen eyes, such as those of a hawk, get their acuity from smaller number of sensory recepotors per ganglion cell (see picture in previous post).
Rod type retinal receptors provide an animal with the ability to notice movement, since they deal only in contrast of light and dark, as some people say black and white. Cone type receptors deal with colour, and allow much greater definition and precision. The human eye has both. In the focal area in the centre of the retina, it is mostly cones with a small proportion of rods; in the surrounding retina, it is mostly rods with a small proportion of cones. Additionally, the human eye's lens flexes to work with varying distances, much like the eyes of certain birds and such. We also have a blind spot in each eye. This is where the nerves leading from each receptor bunch up and run through the retina into the optic nerve. Luckily we have two eyes, and the vision from each eye covers the blind spot from the other side, so usually we never notice. Why do we have such eyes? Look at us. Forward facing eyes and sharp canines of a carnivore. Cutting incisors and flat molars of the herbivore. We are omnivores, and developed the tools to suit that. We needed high-definition stereoscopic vision and also the ability to operate in near-darkness and the ability to discern one type of berry from another.
thank you adam for your summary of our posts Please Register or Log in to view the hidden image! However A single receptor can never pick up higher level information such as structure. Since movement is picked up as changes in structure in thew information, a receptor cells in the retina can never pick it up. One need brain structures for that. (in fact there are some specific regions in the primary visuao cortex concearned with processing of motion in visual information. Again, it is highly unlikely that cones alllow for much greater definition. You must not forhget that the yellow spot in the retina (the focal area) has a completely distinct anatomy from the rest of the eye. It is the difference in structure that makes it more hidef not the type of cells! take care Merlijn
why we see color A pretty good theory of why we see color is that our Ape ancestors needed it to see ripe fruit. Monkeys and Apes aren't very fast creatures, that's why they stick to the trees. It's very advantageous to look across the grasslands and see if the fruit (such as a banana) is ripe or not. The best way to tell ripeness is color. It's very disadvantageous to scamper across the grassland, risking life and limb, only to find that the fruit isn't ripe. The one thing that I don't understand about the evolution of vision is why our ability to see the "blue" spectrum evolved differently from the rest of the colors. I could see how it could evolve first (better twilight and night vision) but the way the brain is set up, it seems to have evolved after the other spectrums. Does anyone have ideas on that? -Xenu
not entirely true For the most part, it's your brain that is covering up your blind spots. Close your left eye, do you see the blind spot? Do you see a big hole in your vision. No. Now hold out your hands in front of you with your index fingers pointing up and side by side, at eye level (still left eye closed). While fixing your left eye on your left finger slowly, very slowly, move your right finger to the right periphery, maintaining the same height. If you do it right, you right finger will disappear. Do you see a black hole now? Again, no. You see a blurry continuation of the background. Your brain is filling it in! -Xenu
Ultimately it's the ratio of photoreceptors to ganglion that determine acuity. As far as I know all cone cells have a 1 cone cell to 1 ganglion ratio, making those ganglions very accute. While rod cells have a many cells to 1 ganglion ratio, making those ganglions less accute but more sensitive to light. The fovea is (almost?) entirely rigged up with cones, a one to one ratio, making it very accute. I don't think Adams claim... is that radical of a leap considering the "wiring" make up of each type of receptors. The disagreement between you two seems like semantics. -Xenu
