View Full Version : Another question on evolving
Speaker for the Dead
07-15-2000, 06:13 PM
I must sound like the complete ignorant person regarding Darwinian Theory, oh well. I have another question:
How come site, taste, hearing, touch (I know THAT one) and smell are so common? How come no animals have the kind of ability as those grey d00ds in 'A wrinkle in time'? That would be very nifty. But honestly, are there any animals that can 'see' the small amounts of radiation that everything emits? Then they'd have excellent vision night OR day... Maybe these are just the delusions of a 13 year old, but I'm honestly curious.
BTW, sorry that I'm too lazy to correct my many typing errors.
07-15-2000, 07:55 PM
Maybe because small amounts of radiation do not give sufficient resolution to be of use to any crature either to find food of avoid becoming food. Huge honking amounts of radiation (such as the fraction of the electromagnetic spectrun that can penetrate our atmosphere) can produce echoes and reflections that are useful for even the most primitive phototropic bacteria.
There are not enough natural strong sources of radioactivity to give an organism the first step towards developing a more sophisticated system. It is very difficult for natural selection to select for something which does not impact the organism's environment significantly.
07-15-2000, 08:39 PM
Rattlesnakies and other pit vipers can sense heat in the form of infrared radiation, and use it to locate prey.
07-15-2000, 08:45 PM
Several aquatic species can sense electrical fields. In sharks, this is due to the organs of Lorenzo (correct if needed).
There is a small african fish which uses electric pulses to communicate to others of the same species. It has been used extensively in neurology experiments. I'll see if I can go find a cite.
07-15-2000, 08:47 PM
Here's a site that has an atlas of the brain of the Apteronotus leptorhynchus, a weakly electric fish.
07-15-2000, 10:06 PM
Interesting question, Speaker. As has been pointed out, there are other senses that we don't have. I'll add to these the possible magnetic sense used by migratory birds and the sonar of bats and dolphins (yes, I know it's technically just hearing, but it's so highly refined to a specific purpose that I'll include it anyway).
My guess as to why the five senses we have are so common is just that they're very useful for the world in which we live. Just think - the ability to see, hear, and smell something coming, the ability to recognize a possible food source by taste, and the ability to know when you've run into something by touch are very useful survival tools. This line of reasoning is supported by the observation that in environments in which one or more is useless, they are quickly lost (think blind cave fish).
As to why there aren't more senses around, off the top of my head, I can't imagine what other field is around strongly enough to make sensing it useful. Electromagnetic has some limited uses (like sharks and migratory birds), but the earth's field is so strong it tends to damp out any others that may be related to life.
07-15-2000, 10:35 PM
Alpha, and Beta radiation are particulate, and are fairly easily blocked by any intervening material, a putative sense organ for detecting those must of necessity occupy the surface of the creature, and in order to have any range detection, occupy a number of different locations. A whole lot of tissue directed toward something which only occurs in very small amounts in living creatures. Difference in levels of alpha and beta radiation present in any given direction conveys very little in useful information for predators, or for their pray in the most likely case where the predator or pray are not specifically radioactive.
Gamma radiation is present in the world in more common amounts, although less differentiated according to any concerns regarding other living things. However there are a number of other reasons having to do with detection of gamma radiation, which make it far less useful to have gamma vision. The wavelength of gamma rays make it extremely difficult to reliably “capture” the rays with any type of normal plant or animal tissue. Chemical processes that would be triggered by gamma rays, and not triggered by much more common light rays are not common in living tissue. Gamma rays do destroy living tissue, so a gamma detector would need to be very active in regenerating its tissue to remain operable.
Directionality of gamma irradiation is very hard to establish. Since it penetrates the stuff of living things it would be hard to tell if the gamma boogey man was behind the elephant, behind you, or right in front of you, if you had to rely only on gamma eyes. Living things that are more common than gamma boogey men are not particularly good sources of gamma rays, and would be invisible. Actually, mountains devoid of gamma sources, the ground below you, a few distant astronomic objects like the sun, and stars, and an occasional lunar eclipse would be pretty much all you could see. Not much payback for this development from a survival benefit point of view.
07-16-2000, 01:48 PM
Wasn't the primary sense of the "grey d00ds" in A Wrinkle in Time hearing? I presume that you're referring to Aunt Beast's species.
As for other regions of the electromagnetic spectrum, many animals can see longer or shorter wavelengths than us, but there are some limitations. For one, if you want to get any sort of resolution, you need sense organs of a size at least comparable to the wavelength of the radiation-- Smaller organs, and you can't determine the direction of the wave, and have a hard time detecting it at all. Since most sense organs are of order a few centimeters across or smaller, this rules out microwaves and radio waves. Infrared can be detected by some animals, notably the pit vipers and some insects, but the resolution is terrible: A viper can sense that there's prey somewhere generally in front of it, say, but it can't pin it down from infrared alone. For shorter wavelengths, ultraviolet is blocked rather efficiently by most organic materials, so you'd need a detector on the skin surface, without any lenses. In fact, the human retina is actually sensitive to UV, but none ever reaches it. Without lenses of some sort, you're not going to be able to resolve images, making it of limited usefulness, although a few birds and insects did manage to evolve UV-transparent lenses. Beyond the UV, you've got X-rays and gamma rays, which would be useful to detect if present (let the creature know to get out of the area), but there's just not much X or gamma radiation around to be worth detecting it. According to the original comic books, Superman's X-ray vision relied on x-rays emitted by his eyes (or some other organ near them) illuminating whatever he was looking at. Unfortunately, it's rather difficult to produce x-rays, and no organism has yet figured out the trick.
07-16-2000, 04:21 PM
Originally posted by TheNerd
Several aquatic species can sense electrical fields. In sharks, this is due to the organs of Lorenzo (correct if needed.)
Ampullae of Lorenzini.
Speaker for the Dead
07-16-2000, 08:55 PM
No, didn't the Beasts (no other name that I remember) have the ability to 'sense' what was around them... THey couldn't see so light differenses didn't effect them, but they knew exactly were everthing was. The author doesn't explain how this is possible.
07-16-2000, 10:13 PM
And since Madeline L'Engle didn't explain how it worked, we're free to postulate that it worked via feeling subtle air currents, or distortions in local electrical fields, or sonar, or any of a host of other possible senses which have, in fact, evolved on Earth. While we're at it, why hasn't any Earthly creature yet developed the ability to tesser? Now, that woud be way cool.
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