Wikipedia:Reference desk/Archives/Science/2008 November 20

= November 20 =

Rotating spherical shells and gravity
The shell theorem says there is no gravity inside a hollow sphere. If that sphere is rotating, is there an acceleration which would be perceived as gravity by someone on the inner wall of the shell? —Preceding unsigned comment added by 128.194.103.45 (talk) 01:13, 20 November 2008 (UTC)


 * If you are rotating with the shell, then yes, you would feel a centrifugal force (and yes, there is such a thing). Its strength would vary depending on latitude (highest at the equator, zero at the poles). You could probably tell it apart from gravity, especially if the shell is fairly small, because of the Coriolis effect. --Tango (talk) 01:59, 20 November 2008 (UTC)


 * Although - if you're thinking of a Dyson sphere - that's not a problem. However, very large spheres have severe stability problems.  SteveBaker (talk) 02:39, 20 November 2008 (UTC)


 * Actually, I was thinking of Pellucidar and why everything doesn't just fall into the central sun (and what IS that central sun burning, anyway?). I imagine one rotation per 24 hours wouldn't provide significant g-force, though. 128.194.103.45 (talk) 04:13, 20 November 2008 (UTC)


 * Since we on Earth don't go flying off from centrifugal force, you could reasonably say that. As I recall, centrifugal force accounts for about a 1% variation in the apparent force of gravity between the equator and the poles.  Someone on the inside would notice a tendancy for things to move towards the surface, but it wouldn't be significant. --Carnildo (talk) 22:36, 20 November 2008 (UTC)


 * It's important to note that this perceived outward force would only be perpendicular to the 'floor' at the equator. The sphere can only spin about one axis at a time, so anybody standing along the equator would feel like they were standing on level ground, but as you move toward the poles, the "gravity" force (actually centripetal force) would decrease but at the same time the perceived slope of the walls would increase. The slope would reach vertical at precisely the same time as the centripetal force disappeared - that's when you reach the pole. Maelin (Talk | Contribs) 02:03, 22 November 2008 (UTC)

The Universe is Red and Purple
I look at the and I see a band of red on the left, and a band of purple on the right, with the tiniest sliver between them that fluctuates colour dramatically. I'm sure we evolved to see only that magical sliver for a reason. My question is: would we function as well, would we have been as succesful, if our eyes lived deep in the red or deep in the purple?

(Ignore this: I was thinking about the subject b/c I'm designing a spacesuit for my pet bat, Franky.  When Franky and I go to the moon, he could never "see" beyond the plate of his helmet's visor.  I feel so sorry for those species that evolved on sonar.) Sappysap (talk) 01:32, 20 November 2008 (UTC)


 * Rather conveniently and probably not coincidentally, the visible spectrum falls at a point where water and the atmosphere in general are relatively transparent. Some birds see a little more in the UV spectrum than humans do. Interestingly enough, according to infrared, that drop in opacity at 10 micrometers corresponds with infrared wavelengths radiated by humans and presumably other organisms emitting heat. 152.16.15.23 (talk) 01:56, 20 November 2008 (UTC)
 * It also coincides quite closely with the frequencies that are emitted most strongly by the Sun. --Tango (talk) 02:07, 20 November 2008 (UTC)


 * Indeed - when you consider what we need our vision to do - that little slot is perfect. If the wavelengths are too long, you can't resolve small objects like the branches that a small furry mammal needs to climb on or not walk into.  You need to be able to see small things like ants so you don't get bitten by them.  On the other end of the spectrum - energetic short-wavelength waves make things transparent - and that's no use either.  Mostly, what we need is to be able to see the relatively subtle difference in color between an unripe fruit, a perfectly ripe fruit and one that's gone off.  For (say) an apple - that's a very narrow range of frequencies - green to red to brown.  Evolution didn't need us to be able to see everything - just the things that allow us to survive and reproduce.  Other animals do see over wider spectrums - but that's because they need to - and we don't. SteveBaker (talk) 02:34, 20 November 2008 (UTC)


 * Maybe you realize this, but those long bands of red and purple in the picture you linked shouldn't be there. Most of those frequencies are outside the visible range and we don't see them at all. The whole picture is pretty sloppily drawn. I can't make sense of the frequency scale on the spectrum (it's kind of logarithmic, but not really), and the visible range is actually far narrower than shown there (assuming a roughly logarithmic scale, it should cover about a tenth of the 1012–1015 Hz range, not half). I'm surprised the image got featured in that state. -- BenRG (talk) 02:51, 20 November 2008 (UTC)
 * I think the purple and red swaths were supposed to artistically illustrate the infrared and ultraviolet part of the spectrum extending off to the sides of the visible. 152.16.15.23 (talk) 03:46, 20 November 2008 (UTC)


 * @BenRG It is featured on Commons, where accuracy is not so much of an issue. A version of this picture failed to become a feature picture on EN in large part due to the colouring issues. I didn't like it then either! Matt Deres (talk) 16:14, 20 November 2008 (UTC)


 * Perhaps organic material cannot refract frequencies that are much lower than red light light, so there cannot be eyes for these lower frequencies. Higher frequencies than blue light are blocked by the atmosphere, so eyes would be useless and would not evolve, even if possible for organic material. —Preceding unsigned comment added by 98.16.67.220 (talk) 02:59, 20 November 2008 (UTC)


 * Infrared can be refracted by plants and other such larger objects because the wavelength is small enough. That's not too much of an issue. A bigger potential biological obstacle might be coming up with a photoreceptor that is sensitive enough to be triggered by an infrared photon (which is lower energy than visible photons) yet will not be falsely triggered by routine thermal temperatures and the infrared light being generated by the organism itself. 152.16.15.23 (talk) 03:43, 20 November 2008 (UTC)


 * The graph shows that electromegnetic radiation with a wavelength of more than 11 meters is blocked by the atmosphere. A note on the diagram also says that. Yet radio waves of much longer wavelength actually are propagated through the atmosphere, as everyone knows.


 * I can't respond with certainty but the reason why the graph shows the atmosphere as opaque is that long radio waves get reflected/interfered with by the ionosphere. 152.16.15.23 (talk) 03:35, 20 November 2008 (UTC)
 * True but the image may count the ionosphere as the atmosphere. You should sign your posts by typing four tildes "~" in a row by the way 152.16.15.23 (talk) 04:04, 20 November 2008 (UTC)
 * Radio waves have to pass through the atmosphere to get to the ionosphere.


 * The ionosphere is part of the atmosphere, specifically the "thermosphere." I think the main point of the image is to show that low frequency radio waves generated from distant space may not penetrate the atmosphere all that well. Regardless, there is probably a of lot noise from solar events and random x-ray bursts colliding with the upper atmosphere and whatnot. The image may be wrong too, but I'm not an expert on the subject... 152.16.15.23 (talk) 04:22, 20 November 2008 (UTC)


 * Talking about the visible spectrum and eyes, there is a MUST READ book called Wonderful Life, by Stephen Jay Gould. It describes small fossils found in the Burgess shale (in the Burgess Pass, Canada). These fossils were the earliest creatures to develop eyes, and the author reaches the fascinating conclusion that the ability to see was the cause of the Cambrian explosion, in which evolution proceeded with great rapidity and in many directions. With eyes, predators could see their prey from a distance, and they developed many ways of catching and holding their prey. The prey creatures also had eyes, and developed many ways to evade the predators. Be sure to read this book.

One more potential evolutionary issue is that the eye does not contain anything like an achromatic doublet that would prevent chromatic aberration. At least, that's true for human eyes and I haven't heard of any species where it isn't true. With the narrow range of wavelengths of visible light, this is not much of an issue; you don't normally notice that your eyes focus red light a little differently than they focus blue light. If our eyes had evolved to see a much wider spectrum of wavelengths, they would need some other sort of improvement in order to see as sharply as we do. Whether this has actually been a factor in evolution I can't say, but it makes sense. --Anonymous, 04:57 UTC, November 20/08.


 * The yellowness of the lens blocks shorter wavelengths which the retina would otherwise be able to see, but which would make the chromatic aberration worse. People who have had the lens removed to correct cataracts can see near UV wavelengths the rest of us can't, unless they get a lens implant which blocks the shorter waves. An evolutionary compromise in favor of resolution over sensitivity. Edison (talk) 06:03, 20 November 2008 (UTC)


 * In order to prove that some "design feature" (pardon the term) is the result of "evolutionary compromise", you not only need to demonstrate that it has an advantage over some alternative that might exist, you also need to demonstrate that the alternative has existed and found wanting. In other words, you don't just need to show that the lens has this property; you also need to show evidence that an earlier form of the species, or a less successful related species, had lenses that did not block those shorter wavelengths.  Otherwise you're guessing: the alternative hypothesis would be that the lens is that color because the yellowish material was the first one that evolution produced that was good enough for a lens such as we have.  I don't have any information like that, and that's why I said I don't know. --Anonymous, 09:53 UTC, November 20/08.

A little earlier in this discusion of electromagnetic radiation, I wrote "Perhaps organic material cannot refract frequencies that are much lower than red light light". What I meant was that perhaps all organic material is opaque to frequencies lower than red light, and perhaps it is not possible for living things to develop an organic material of that type. —Preceding unsigned comment added by 98.16.67.220 (talk) 13:36, 20 November 2008 (UTC)


 * I said that it may be impossible for living things to develop an organic material that is transparent to electromagnetic radiation lower in frequency than red. However, pit vipers have an organ on each side of their head that is sensitive to heat. By this means they can detect their prey, even in darkness. There is apparently no lens so there is no refraction, but the organ is quite complex. Could there be some other form of focussing, refractive or otherwise? The organ is extremely sensitive to slight differences from the background heat. I wonder what the resolution is. See "pit viper" in Wikipedia. —Preceding unsigned comment added by 98.16.67.220 (talk) 13:58, 20 November 2008 (UTC)


 * The pit organ is essentially a low-resolution pinhole camera, which works by limiting how much of the world can illuminate any given part of the pit. --Carnildo (talk) 22:56, 20 November 2008 (UTC)


 * Carnildo, thanks for that word "limiting". It made me realize for the first time how a pinhole camera really works. —Preceding unsigned comment added by 98.16.67.220 (talk) 06:21, 21 November 2008 (UTC)

The diagram for this topic shows a vertical band of purple. Purple is a combination of red and blue, which are at opposite ends of the visible spectrum. Where did that crazy diagram come from? —Preceding unsigned comment added by 98.16.67.220 (talk) 06:17, 21 November 2008 (UTC)


 * There are actually two forms of the color purple: the red+blue that you refer to, and actual purple light: wavelengths shorter than blue but not so short they can't be seen. Because the red sensors in the human eye are also slightly sensitive to blue, the two forms look the same, giving us the color wheel you're familiar with. --Carnildo (talk) 23:43, 21 November 2008 (UTC)


 * The color band in the diagram is violet. It leads into the invisible ultraviolet. If I correctly understand the description of violet in Wikipedia, it is the color at the high-frequency end of the visible spectrum. The word "violet" can also refer to the mixture of red and blue - not a spectral color. The word "Purple" refers always and only the mixture of red and blue. I think the title of this thread should be "The Universe is Red and Violet". —Preceding unsigned comment added by 98.16.67.220 (talk) 00:39, 22 November 2008 (UTC)

Restarting the Earths spin.
Apparently the Earth will slow down to a stop after a long time, which will be hard on the nations facing away from the sun. Would a large gyroscope on a big enough motor planted in the North pole be able to slowly spin the Earth back up? Trevor Loughlin —Preceding unsigned comment added by 80.0.106.90 (talk) 03:34, 20 November 2008 (UTC)


 * Assuming, of course, such a stop will happen before the sun engulfs the earth as a Red Giant. According to our article on the subject:  the earth is slowing down at a rate such that 2.3 milliseconds are added to the day every century.  At this rate, the day will reach 25 hours (as measured on our scale) 828,000,000 years in the future, and the day will be twice as long as it is now (i.e. 48 hour day) 19,872,000,000 years in the future.  By comparison, the Sun will reach "red giant" phase, at which point it will likely engulf the earth, in a mere 5,000,000,000 years.  The earth is not going to stop before it is destroyed... --Jayron32. talk . contribs  04:00, 20 November 2008 (UTC)


 * And even if it did - the amount of energy required to spin it back up again would be immense - more than we could possibly obtain by any means I could imagine. Worse still - because of conservation of momentum - in order to spin the enormous mass of the earth up to a 24 hour rotation period would require spinning something else just as heavy in the opposite direction with a 24 hour rotation period...or something half as massive to a 12 hour rotation - or a quarter as massive to a 6 hour rotation.  What you'd find (and it's too late in the evening for me to crunch the numbers - so this is a guess) would be that for a sensibly massive, buildable gyroscope to provide enough inertia to equal that of the earth would require it to spin so fast that it would fly apart no matter how strong the material it was made from.  So I don't think it's a practical engineering possibility so spin a planet up to any kind of useful speed.   But as Jayron correctly points out - it's not going to be a practical problem. SteveBaker (talk) 04:28, 20 November 2008 (UTC)


 * Honestly, I wouldn't mind a couple extra hours of sleep at night. That's one of the reasons I look forward to Mars colinization. ;) 216.239.234.196 (talk) 13:26, 20 November 2008 (UTC)


 * The folks a million years ago probably could not imagine the levels of energy we posses now, so logivcally, we cannot forsee the technology of a million years in the future (assuming there are still any people around). Maybe Earth's aliens, robots, or Uber cockroaches will have figured out ways to exert force on a planet-spinning level. Edison (talk) 06:00, 20 November 2008 (UTC)
 * According to the Kardashev scale we will get there a lot faster than in a million years. We are already 72% on the way to a Type 1 civilization, which is the minimum power we would need to get our planet spinning again. Sandman30s (talk) 11:18, 20 November 2008 (UTC)


 * Rather than "stopping" with one side permanently facing the Sun, Earth is much more likely to become tide-locked to the Moon. —Tamfang (talk) 09:06, 20 November 2008 (UTC)


 * Not to worry, the Sun is gradually getting warmer. In about a billion years, it will be too warm for liquid water to exist on Earth, wiping out all life on the planet.  216.239.234.196 (talk) 13:24, 20 November 2008 (UTC)
 * OH MY GOD! What a shock! I misread the previous post, and for a minute I thought that "all life on the planet" only had a million years to live! Edison (talk) 00:33, 21 November 2008 (UTC)
 * Thing that bothers me is the the speed of the path leading to that end, and what conditions for existence is that life existing under until the point of annihilation (if not all life, then species by species being wiped out every week). Perish the thought, but...there it is – the slanty bit to doomsday. Julia Rossi (talk) 00:40, 21 November 2008 (UTC)
 * I calculated in a recent answer to a similar question that it would take over 5 TRILLION years for the earth to cease rotating at the current rate of decrease (1.7ms per century) - so not exactly an urgent issue. Exxolon (talk) 03:16, 22 November 2008 (UTC)
 * I think you calculated the time it takes the rotational period to reach 48 hours. --Bowlhover (talk) 07:59, 23 November 2008 (UTC)

Compounds:both ionic and covalent
Which compounds are ionic in solid state AND covalent in vapour state? --Siddhant (talk) 10:13, 20 November 2008 (UTC)
 * Strong acids are a class of compounds which are covalently bonded, but are also strongelectrolytes; i.e. they are ionic in the "aqueous" state. At room conditions, all strong acids are either gases or highly volatile liquids; they may form ionic solids in the solid state; I am not sure on that one.  What you are probably looking for is a compound with highly polarized covalent bonds, such that the lattice energy of the solid form of the compound is greater than the bonding energy of at least one of the covalent bonds in the gasseous phase.  It make take some research to find them; but your best guess is to look for compounds with bonds between elements with an electronegativity difference very close to 1.5 .  That number is generally taken as the "boundary" between a "polar covalent bond" and an "ionic bond".  Compounds that lie RIGHT on the line are likely to display some hybrid behaviors between the two.  As one real example, ZnCl2 has an electronegativity difference of 3.16-1.65 = 1.51 .  Zinc Chloride is definately an ionic solid, but also has a low melting and boiling point, and displays some molecular character at higher temperatures.  I know for a fact that SnCl4, aka Tin(IV) chloride is in fact a molecular substance (despite being a metal-nonmetal compound) as it is a liquid at room conditions.  --Jayron32. talk . contribs  14:05, 20 November 2008 (UTC)

What about PCl5?--Siddhant (talk) 06:20, 22 November 2008 (UTC)
 * Yeah that one looks like it fits. See Phosphorus pentachloride. --Jayron32. talk . contribs  06:31, 22 November 2008 (UTC)

PCl5 is definitely yes. Also AlCl3? See this link the period three chlorides. Has some nice information (which wikipedia can use). Are there more than two such compounds? --Siddhant (talk) 08:53, 22 November 2008 (UTC)

genius of firefox
hello wikipedia,

i've recently downloaded firefox 3.0 and am just wondering how the 'ominibar' works. if you type a phrase/word (i.e. not a complete web address) it either directs you to the wikipedia entry, the google search results or the actual specific website. what amazes me is that it so accurately reflects what i want- 90% of the time its like its reading my mind! What i'd like to know is how, when i type 'gmail' (for example) does it know i'm looking for the website and not the wikipedia entry on gmail, or indeed, the search results for gmail? What's the algorithm involved does anyone know? thanks, 82.22.4.63 (talk) 14:02, 20 November 2008 (UTC)
 * Here's one of Mozilla's blog posts about the subject. In short, the bar runs a search on your history and bookmarks, both against the URL text and against plain-text titles.  If no option is selected (that is, you type text and press enter), it throws that string to a search engine -- though that functionality isn't anything revolutionary. &mdash; Lomn 14:10, 20 November 2008 (UTC)

While we're up: when I type something in (for example) WP's search box, where does the list of suggestions come from? They're clearly not from my history. —Tamfang (talk) 19:52, 20 November 2008 (UTC)
 * It's from the list of all Wikipedia page titles starting with your string. Algebraist 20:02, 20 November 2008 (UTC)
 * So does Firefox keep a list of these? How often does it update? —Tamfang (talk) 08:50, 21 November 2008 (UTC)
 * It's done by Wikipedia, not by Firefox. It should be documented somewhere, but I can't find it. AFAIK it updates as soon as a new page is created. Algebraist 09:30, 21 November 2008 (UTC)

Maybe my question wasn't concrete enough. If I enter a keystroke in the search box, a popup menu appears, very quickly. Does Firefox get that list from Wikipedia (or perhaps some other cache) before or after I start typing? Before seems wasteful; after seems impossible. —Tamfang (talk) 20:38, 21 November 2008 (UTC)


 * I'm almost sure it's after you start typing. It only grabs a dozen or so articles at most, so if you just type in an "s", it just grabs the first 10-12 articles that start with "s" and keeps moving from there. Since it's all sequential anyway, I doubt it's much of a hassle to grab that quickly. Matt Deres (talk) 21:10, 21 November 2008 (UTC)


 * Okay. —Tamfang (talk) 04:08, 22 November 2008 (UTC)


 * The browser (Internet Explorer for me, but I suspect Firefox is no different) does keep a cache of the lists, as shown by the fact that lists I've already seen still appear after I disable the Internet connection. --Bowlhover (talk) 07:01, 23 November 2008 (UTC)

Evolutionary Mammal Anatomy Blunders
A while ago, my biology teacher recited a list of evolutionary mammal anatomy blunders such as our trachea is too close to our esophagus. Thus one can easily die from choking. What are the other evolutionary mammal anatomy blunders? Please note that this is not a homework question. I am curious and just trying to remember. --Emyn ned (talk) 14:26, 20 November 2008 (UTC)
 * The human knee has always struck me as proof of Idiotic Design. DuncanHill (talk) 14:28, 20 November 2008 (UTC)

Why so, Duncan? --Emyn ned (talk) 14:35, 20 November 2008 (UTC)


 * Have you ever tried using a pair? They are too loose for walking or running efficiently, not loose enough to be able to sit on the ground comfortably, and if you kneel on them they complain. DuncanHill (talk) 14:43, 20 November 2008 (UTC)
 * I know. I tried praying on my knees for them to get better, and it only made them worse. Myles325a (talk) 03:48, 27 November 2008 (UTC)
 * Just go through a list of common ailments and causes of death - a significant number could probably be avoided by a slight modification to our anatomy (although doing so would undoubtedly introduce different problems). --Tango (talk) 14:38, 20 November 2008 (UTC)
 * Just so everyone is clear, Evolution cannot make blunders, because it is not a directed, thoughtful process. Though the trachea is too close to our esophagus, it is hardly a blunder, it is actually quite efficient to use one orifice to perform two functions.  In fact, it may be "safer" for a vertebrate to have one location for both intake of oxygen and consumption of food, because there is a decrease in infection rates with fewer openings to the environment.  Also, and this is critical, evolution cannot create parts, it has to make do with what you have.  For example, a facial nerve in a shark shifts position in humans to control the diaphragm and breathing.  Evolution is incredibly efficient in utilizing whatever we have available.  But in the end

evolution is driven my random mutations, genetic drift and natural selection, none of them very intelligent. And of course, in a few million years, after a certain group of humans dies out because it keeps choking on it's food, maybe some flap in the trachea keeps this from happening. Oh yea, we've already evolved epiglottis, which prevents that from happening. So, if I were a student in your teacher's class, I'd tell him he needs to return to college and refresh his training in biology, because he's completely and utterly wrong. Orange Marlin Talk• Contributions 14:58, 20 November 2008 (UTC)


 * Further, given how important the sense of smell is to the ability to sense food as well as simply sensing things in the air we breathe (two survival advantages), it makes a lot of sense that the smelling organ can be positioned at a shared region of "breathing" and "eating". DMacks (talk) 15:37, 20 November 2008 (UTC)


 * The word "blunder" was used in a rhetorical sense. Could it be said that God has blundered? No, God has allowed evolution to proceed without divine interference, just as God has given men free will to do good or evil. —Preceding unsigned comment added by 98.16.67.220 (talk) 15:24, 20 November 2008 (UTC)


 * Evolution does not involve the existence of any supernatural being.  Orange Marlin  Talk• Contributions 00:18, 21 November 2008 (UTC)


 * That's what I said. God does not get involved.


 * The uneven occurrence of human intelligence is an evolutionary "blunder". Most humans are still cave men; they can learn (remember) but they cannot create. All they are basically suited for is a hunter, gatherer, fighter, existence. Less than one percent of humans - the intelligent minority - has created civilization. The rest simply copy what the intelligent ones have shown them. The primitive ones nearly always have control of government, and as a result of their cave man instincts they often take their country into war, using advanced weapons placed in their hands by the intelligent ones. Eventually the human race will destroy itself - through industrial pollution, if not through nuclear war. The intelligent ones will be responsible - the cave men didn't know any better. The intelligent ones weren't moral enough - they put their brains at the service of cave men. From the standpoint of evolutionary history, civilized mankind will have lasted only a very short time indeed. There was a very patchy development in IQ without an accompanying development in MQ (moral quotient) in all humans. —Preceding unsigned comment added by 98.16.67.220 (talk) 15:40, 20 November 2008 (UTC)


 * There is an article on maladaptation, which might be related to what you had in mind, though it doesn't quite answer your question either. ---Sluzzelin talk  16:29, 20 November 2008 (UTC)


 * Kurt Vonnegut still has Internet access, apparently. --Sean 18:32, 20 November 2008 (UTC)


 * A couple of non-optimal designs spring to mind:


 * 1) The blood vessels for the retina are on top of it, not behind it, causing a blind spot.


 * 2) Having the spinal cord inside the spine may make sense for quadrupeds, but not for bipedal humans. Something more like a notochord would make more sense for the nerves, and could run parallel to the spine but more toward the front of the body.  The spine, on the other hand, could contain a rubbery chord in the center without any nerves.  This design would hopefully eliminate pinched nerve injuries and paralysis when the spine is broken, and strengthen the spine, as well. StuRat (talk) 23:25, 20 November 2008 (UTC)


 * Sexual selection has played all sorts of havoc over the evolution of morphological or anatomic characteristics, that on the face of it, may appear to be unfavorable. For example, after too many pints how many men (or indeed women) have rued the day our baculum was selected against? And all those pale, freckled gingers from the Celtic nations? Not so great when you spend the Glasgow Fair largin' it in sunny Ibiza. Rockpock  e  t  23:41, 20 November 2008 (UTC)


 * Chromosomal shortening at the telomeres as a results of replication seems inefficient. Calamus Fortis  00:07, 21 November 2008 (UTC)


 * Actually, that may well provide an evolutionary advantage by killing off older people and allowing their resources to be used to raise their descendants. Shorter lifespans allow for faster adaptations to changing conditions and hence increase the chance that those genes will survive. StuRat (talk) 03:45, 21 November 2008 (UTC)


 * Response to StuRat. Again, since eye evolution is not "designed" by anyone, the blood vessels must exit the eye someplace, causing the blind spot.  Given what was available genetically and morphologically, as evolution of the eye progressed, the construction of the eye as it is must have some advantage to the organism over other possibilities.  As for bipedal humans, the spine works perfectly as a protective shield to the spinal cord.  Who knows what will be there 20 million years from now.  By using the word "design" you imply that there was conscious choice in how evolution proceeded.  There isn't any, so the eye and spine we have, must have had some advantage over alternative evolutionary pathways.   Orange Marlin  Talk• Contributions 00:17, 21 November 2008 (UTC)


 * We all realize that evolution has no "designer", but our language often fails us when we try to talk about the results of evolution. I tried to get past this problem by saying "sub-optimal designs".  I don't necessarily think that a design implies a designer, as you could say "those freckles on your face make a nice design", even though nobody planned them that way.  But, much as we say "the Sun has risen" when the Earth has really rotated so that the Sun has come into view over the horizon, I think it's fine to use words like "blunders" when talking about evolution.


 * I also don't buy your argument that "the eye and spine we have must have had some advantage over alternative evolutionary pathways". That would only be the case if all evolutionary pathways had been tried.  Only a small portion of them have been.  Then there is the issue of gene-linkage.  Perhaps there were better evolutionary pathways tried but they were on the same chromosome as a gene which caused more harm than that advantage, so died out. StuRat (talk) 03:35, 21 November 2008 (UTC)


 * Blind spot is actually a good example of an evolutionary blunder. Note that cephalopods have the blood vessels existing behind the retina and have similarly good arrangement with the nerve endings so they have no blind spot. The issue here is a bit more subtle; blind spots aren't a big deal and once the mammalian eye was set up the way it is it is difficult to evolve away from that and there's little incentive to do so. Keep in mind that evolution generally only makes moves that are either neutral to local fitness or improve local fitness. Thus, one something has evolved in a more or less suboptimal way if there's no simple mutational fix or then evolution won't move to fix it. One helpful analogy might be to think of evolution as an ant that is taking a semi-random walk trying to find high points on a bumpy surface. The ant cannot see points that are far away even if they might be much higher. JoshuaZ (talk) 01:08, 21 November 2008 (UTC)


 * No offense, but this is a singularly silly subject. Basically we are assuming that "x" is a blunder because it is not "y" .... or "z" or any other letter you wish to choose.  As we can only but guess what a creature's existence would be like if x were y (seemingly better) we can but hypothesise re that alleged "improvement".  Ah, but if x were y, would c be c or would it have been d?  Then given that change would n still be n ot would it be p?  Think it through, woud these changes represent an improvement, or would they so signifcantly change life aswe know it that we'd not be having this discussion?   &#0149;Jim 62 sch&#0149; dissera! 01:42, 21 November 2008 (UTC)


 * Not really. We can ask "if a given organism X has fitness f(X), and we put in organism X' in that situation would we have f(X')> f(X)". This is well-defined both biologically and mathematically and biologists talk about it all the time. The most relevant Wikipedia article is fitness landscape. JoshuaZ (talk) 01:47, 21 November 2008 (UTC)


 * OK, it's not silly, agreed. I was being pissy.  &#0149;Jim 62 sch&#0149; dissera! 01:52, 21 November 2008 (UTC)


 * Also, one of the misconceptions about evolution is that it will only preserve those traits which are "best" and that, through evolution, all life is somehow "improving". That's not the case at all.  Evolution preserves any trait which does not kill the carrier of the trait before it had the chance to breed.  Basically, a trait will be passed on not because its the best, but merely because it didn't kill you.  Also, life isn't "improving", its merely constantly changing in response to environmental changes.  Life isn't always getting better, its merely getting different.  --Jayron32. talk . contribs  03:41, 21 November 2008 (UTC)


 * Sure, but life as a whole is "improving" because the traits that happen to be preserved just because they're not lethal don't become widespread. Only traits offering an advantage to a species become more common in that species' population.


 * Some blunders could be/include Vestigial organs, for instance wisdom teeth. EverGreg (talk) 12:23, 21 November 2008 (UTC)


 * It has been postulated that wisdom teeth were useful to our evolutionary forbears, who were herbivorous. These molars helped them grind their vegetable food. The human race has become omnivorous and fewer molars are now needed. Also in the course of evolution, the human jaw seems to have become smaller, causing crowding of teeth at the rear of the jaw. Hence, impacted wisdom teeth. (See wisdom teeth in Wikipedia.) I wonder what the advantage of a smaller jaw has been. Could it be random change with no use? Evolutionary change has been thought to be advantageous (survival of the fittest). Could some evolutionary change be meaningless - neither good nor bad, just change? Actually, as far as wisdom teeth are concerned, a smaller jaw is a disadvantage. Could there be an offsetting advantage? —Preceding unsigned comment added by 98.16.67.220 (talk) 14:45, 21 November 2008 (UTC)


 * Wisdom teeth may be a case of seeing an evolutionary change that's only halfway complete. If your diet is high in vegetable matter, a large grinding surface is an advantage.  As you increase the amount of meat in the diet, a smaller jaw with better leverage for cutting and tearing becomes advantageous.  Jaw size and number of teeth are controlled by different genes, though, so after you've got the smaller jaw, you need a second evolutionary step (and a corresponding selective pressure) to get rid of the wisdom teeth. --Carnildo (talk) 23:59, 21 November 2008 (UTC)


 * Perhaps wisdom teeth should be called stupidity teeth. They no longer have a use and sometimes cause trouble. —Preceding unsigned comment added by 98.16.67.220 (talk) 03:14, 22 November 2008 (UTC)


 * This issue often pops up in watchmaker analogy-type evolution debates, and in that context, I've read a detailed "design review" of the eye a few years back. This article covers most of the points, but I also remember reading that the lens is controlled by six muscles; only three are needed.  This Talk.Origins archive] gives a much more comprehensive list of less-than-optimal design.
 * As for whether the word "design" is appropriate, I don't see why not. Evolution, as a process, can be considered a conscious designer in the same way that the brain is conscious even though its cells are not.  --Bowlhover (talk) 06:45, 23 November 2008 (UTC)

Egg nutrition
Aside the size, does the chicken eggs and quail eggs have the same nutritional value? The article on Egg (food) only mention nutrition value of mostly eaten chicken eggs. Does nutrition vary on eggs size? --202.168.229.245 (talk) 14:59, 20 November 2008 (UTC)
 * Take a look here and here (set them both to "100 grams" for a fair comparison). The biggest difference seems to that quail eggs have about twice the cholesterol of chicken eggs.  --Sean 18:38, 20 November 2008 (UTC)

BACON...cholesterol
I'm trembling to ask, but does bacon contain the 'good' kind of cholesterol??

My heart says no, but my head says yes, yes, yes!!! —Preceding unsigned comment added by 94.27.160.199 (talk) 19:21, 20 November 2008 (UTC)

Kosher bacon has no cholesterol. In fact, it is nonexistent. —Preceding unsigned comment added by 98.16.67.220 (talk) 19:29, 20 November 2008 (UTC)
 * In fact, many approximations of kosher bacon exist. They're just not pork bacon.  Depending on the variety (and how far you're willing to stretch your definition of "bacon"), they may be cholesterol-free -- tofu bacon would certainly seem to qualify. &mdash; Lomn 19:48, 20 November 2008 (UTC)
 * Or lean chicken breast. —Preceding unsigned comment added by 94.27.160.199 (talk) 20:52, 20 November 2008 (UTC)
 * Actually, the focus on dietary cholesterol is probably a red herring, nutritionally speaking. The way that your body processes the foods it intakes, there is little correlation between macronutrients you eat (such as lipids, carbohydrates, and proteins) and how your body makes its own lipids, carbohydrates, and proteins.  For a long time, the adage "you are what you eat" has really produced some starkly bad nutritional advice; its also entirely not true.  Eating higher cholesterol foods does not raise cholesterol; eating higher fat foods does not raise your body fat in any direct way.
 * When doctors tell you that you need to lower your cholesterol its not because cholesterol is itself harmful; cholesterol is a symptom of an underlying problem. Its like having a runny nose.  The runny nose is not itself a disease, but is an indicator of infection.  Likewise, your cholesterol numbers (and all 3 are important, your total cholesterol, your LDL cholesterol, and your HDL cholesterol) can tell doctors that there is an underlying problem, but the cholesterol itself is no more than an indicator of that problem.
 * Now understanding the function of cholesterol is important to understand why these numbers are so important. Cholesterol is an important structural component to every cell in your body.  When your body needs to make extra tissue, the liver produces the cholesterol from availible lipids (and its important to note that your liver does this even if you ingest no cholesterol in your diet.  Your liver can even make cholesterol from just about anything, even if you take no lipids in at all.).  Also, as your body breaks tissues down, the cholesterol is sent back into the blood stream, where the liver can take it and break it down to make other stuff as needed.  Now here's where it gets really important: your body needs to be able to distinguish between these two cholesterols; that is the cholesterol destined for your tissues to make stuff, and the cholesterol destined for your liver to be recycled.  However, its just all cholesterol, so you need some "marker" to determine where the cholesterol is headed.  Its sort of like a train ticket.  Some of the cholesterol bears an "outbound" train ticket, and some bears an "inbound" train ticket.  Those tickets take the form of lipoproteins, which tag the cholesterol molecules for their destination.  Cholesterol heading from the liver to the rest of your body is tagged with LDL (or low density lipoprotein) markers, while that headed towards your liver is tagged with HDL (or high density lipoprotein) markers.
 * If you haven't seen where this is going, and some of you may, here's the most important bit. Having high LDL levels means that your body is making lots of new cells.  An adult body should probably not be making lots of new cells, aside from general maintenance, so elevated LDL levels means that your body is probably busy making lots of fat cells, which is the primary way in which an adult can "grow".  If you have elevated HDL levels, this is an indication that your body is primarily breaking down these fat cells, and transporting the products back to the liver, which is generally pretty healthy thing to be doing.
 * Now back to the nutritional aspect of this. The body makes all of these compounds on its own, irrespective of what you are eating.  It is going to do this cycle regardless of whether you eat a high fat diet, a low fat diet, lots of carbs, little carbs, etc. etc.  Your body doesn't wait for cholesterol and fats and decide what to do with them when they arrive, it is going to make them or break them down as conditions dictate.  The most important factor in deciding how your body is going to operate in this manner (i.e. will it be involved primarily in making fat tissue or breaking it down) is what is known as blood glucose level.  Elevated blood glucose levels tell your body that you have eaten more calories than you are using, and your body, not being wasteful, starts to put this energy away in long-term storage, which is, you guessed it, fat.  Elevated glucose levels are caused whenever you eat too many calories for your level of activity, so the way to signal your body to produce the good cholesterol is to keep this glucose level low; i.e. either eat less food or exercise more.
 * What is the upshot of all of this? Well, don't feel bad about eating bacon.  Go ahead, because eating bacon in-and-of-itself isn't going to raise your cholesterol level.  However, knowing that you ate that bacon, you should probably eat less of something else (like say, have 1 waffle instead of 2) or go run an extra mile.  --Jayron32. talk . contribs  20:51, 20 November 2008 (UTC)


 * That seems to be entirely too rosy of a picture. Bad cholesterol in the circulatory system is actually the cause (or at least a contributing factor) of plaque formations, which can ultimately cause heart attacks, strokes, and other problems. And bacon does indeed include bad cholesterol, whereas vegetable fats, like avocado and most salad dressings, tend to contain good cholesterol fats. StuRat (talk) 22:55, 20 November 2008 (UTC)


 * That is entirely true, however the blood cholesterol level has really very little to do with ingested cholesterol. Metabolism just doesn't work that way.  The bad cholesterol IS in fact the source of many things such as artierial plaques, which are quite dangerous.  However, this cholesterol is made by the liver and sent to other parts of your body.  Any cholesterol that you eat is digested before being processed.  The LDL-cholesterol in your blood is not there because you ate it.  Just as a runny nose if left untreated may lead to a sinus infection, high LDL-cholesterol levels if left untreated can do nasty stuff to the body; however cholesterol is still not the primary cause of the problem.  The primary cause of the problem is elevated blood-glucose levels, caused by an imbalance between diet and activity level.  And to correct StuRat, only animal-derived cells contain cholesterol.  Plants do not make any cholesterol.  Bacon contains lots of saturated fats; which given their difficulty in digesting do lead to all sorts of health problems.  Vegetable fats tend to be unsaturated fats, which are easier for your body to digest, and so are generally seen as "healthier".  But vegetables contain no cholesterol at all.  Once again, there is a confusion here between cholesterol and fatty acids.  Both are classified lipids, but the production, disgestion, metabolism, and use of them in the body is not at all the same! --Jayron32. talk . contribs  03:28, 21 November 2008 (UTC)


 * Yes, I confused good and bad fats with good and bad cholesterol. I'd still like to see some proof that dietary cholesterol has no effect on our health, however.  Do you have any sources ? StuRat (talk) 03:56, 21 November 2008 (UTC)


 * Oh, you are probably right. I may have overstated the case some.  Certainly dietary intake of cholesterol DOES matter some.  However, the single-minded focus on the cholesterol molecule has placed a out-of-proportion focus on intake of cholesterol.  The greater problem for overall health is persistant elevated blood glucose levels, brought on by an out-of-balance diet and activity regimen.  There is no real adverse health problems associated with eating an occasional piece of bacon, so long as a) your diet is balanced (i.e. you don't subsist SOLELY on bacon) and b) your overall caloric intake is low and your activity level is high.  That basic relationship is probably the most important for determining overall heart and vascular health more than anything.  Eat some bacon once in a while, just be sure to also keep your diet balanced and apporpriate.   --Jayron32. talk . contribs  06:32, 21 November 2008 (UTC)


 * I hate to ask this, but, could you tell us whether you have or ever had anything that might be construed as a financial or family interest in anything related to bacon?94.27.160.199 (talk) 20:57, 20 November 2008 (UTC)


 * I am a semi-retired chemistry teacher, and current "stay at home" parent of a 2 year old. My parents are a retired hospital receptionist, and a service technician for a computer printing equipment firm.  My grandparents were a) a nurse b) a machinist c) a homemaker and d) a shoe store manager and salesman.  I have no connection to any food service industry at all.  But I do get annoyed when gross misunderstandings of physiology lead to poor nutrition advise... --Jayron32. talk . contribs  22:45, 20 November 2008 (UTC)


 * The world is filled with urban myths and such. I'm sure if I had a reasonable diet of Big Macs and fries in reasonable amounts, with lots of exercise, no smoking, etc., I could live a long time.  Or not.  Because so much depends on genetics, bad luck, and many other things.   Orange Marlin  Talk• Contributions 00:22, 21 November 2008 (UTC)


 * I don't think it's possible to be healthy on a diet of just Big Macs and fries, as you would be missing some important nutrients we get from veggies, etc. However, a small portion of your diet could be BMs and fries, as long as the rest of your diet was healthy. StuRat (talk) 04:01, 21 November 2008 (UTC)


 * Here's the nutrition data for an ounce of pan-fried bacon, but it doesn't distinguish between good and bad cholesterol: . StuRat (talk) 23:08, 20 November 2008 (UTC)


 * Thanks Jayron32 for your concise and thorough explanation - better than any Doc (who was allowed to give medical advice) ever did for me :) - I'm sure you'll take some hits for your candor.  -hydnjo talk 00:27, 21 November 2008 (UTC)


 * If you'd really like to start worrying about your breakfast consider this: frying or grilling your bacon produces Nitrosamine which is known to cause cancer. This goes for some "heart healthy" varieties like turkey bacon, too. see liquid smoke  There is a way to inhibit nitrosamine formation by adding ascorbic acid.  If you then add a diet soda, however, you might end up with benzene in your test tube (=body).  You can compound the problem by adding cheese and a pickle.  In our best efforts to feed the ever growing masses foods that taste better than the sawdust a lot of it is made from and neither kills them off nor makes them ill in unacceptable numbers we often identify culprits to be avoided and end up being led up the garden path.  Remember we ended up with trans fats because butter was deemed unhealthy. Simple truths like eat less and exercise more no one wants to hear because they don't fit the way we live.  "Life is dangerous to your health." - Just a thought. 76.97.245.5 (talk) 04:44, 21 November 2008 (UTC)

It has never been shown to cause cancer in humans. One telling difference between humans and the animals in which nitrosamine has been shown to cause cancer is that humans have a long history of eating scorched animal flesh. Hamsters... not so much. Of course we are exposed to a lot of nasty chemicals in this modern world in which we live, but you can't take something that has been shown in an animal model (even if the model in question is a primate, but especially if it's a rodent) and say that it happens in humans. For that, you need research in humans. --121.127.209.126 (talk) 00:44, 22 November 2008 (UTC)


 * And then I read the reference that the "nitrosamine causes cancer" statement in our nitrosamine article points to. It's a toxicological evaluation of nitrosamine in condoms. Its evaluation: Safe. --121.127.209.126 (talk) 00:52, 22 November 2008 (UTC)


 * And then I read the other reference on the page and it was a useful epidemiological study. That makes it more likely to be relevant. --121.127.209.126 (talk) 00:57, 22 November 2008 (UTC)


 * I also have to argue with your assertion that animal studies are useless. If a given chemical causes cancer in animals, it's quite likely to also cause cancer in humans.  It would be unethical to intentionally expose people to a chemical that is a suspected carcinogen in order to perform such a test.  Also, animals are frequently exposed to much higher levels than humans in the test.  If it only causes cancer in one in a million subjects at the usual exposure level, this would be difficult to detect in animal testing, requiring tens or hundreds of millions of subjects.  However, by increasing the exposure level you can also increase the cancer incidence, if it is indeed a carcinogen, to a level which can be detected in animal tests.  So, in conclusion, if animal tests show a chemical is a carcinogen, we should play it safe and avoid the chemical wherever possible. StuRat (talk) 06:54, 22 November 2008 (UTC)


 * The other issue is that while it's true that humans have long been eating scorched flesh, the selective pressure for many times of cancer is not great since very frequently they may have died long before any cancer would take hold. Nil Einne (talk) 09:03, 22 November 2008 (UTC)


 * It doesn't take very much pressure to change the genes, I would have thought it is pretty certain that we have some adaptations for eating scorched food and for protecting against any cancers from it by now. Older members of the community can help bring up the children. Dmcq (talk) 11:07, 22 November 2008 (UTC)


 * Let's say that eating scorched food will only kill one in a million people before they can pass on their genes and that 1% of the people are somehow immune to this effect. Then, after one generation, one part in a million of the 99% will have been eliminated from the gene pool.  By my calcs, somewhere in the neighborhood of 1.000001% would be immune in the next generation.  You can see that the entire human population won't be immune anytime soon, at that rate.  You might argue that a one in a million chance of getting cancer is insignificant, but, in the US that would mean 300 people would die from cancer before they can pass on their genes and likely far more after.  That's significant enough to ban a chemical (if there are non-carcinogenic alternatives), or just put out an advisory, if no substitute is available.  In the case of scorched food, just telling people not to eat food that's burnt to a cinder is likely to work.  Incidentally, this might be exactly how people develop an immunity to dying from eating burnt foods, by developing an aversion to eating such foods. StuRat (talk) 16:27, 22 November 2008 (UTC)
 * It's not just having the children that matters, it's that the children grow up on an equitable basis with others. That's what I was saying about older people mattering. And yes it would have to affect at least 1 in 100000 rather than a million and probably more like 1 in 10000, which if it is detectable in animals it probably would. Dmcq (talk) 17:57, 22 November 2008 (UTC)


 * Yes but although older people help they aren't essential. The children might be slightly worse of then other children but by how much? If the chances of survival is reduced by 1 to 10000 and the chance of an old person dying is 1 to 1000000 then that's still a very small effect. Genetic drift could easily have a far greater effect. Remember as well when we say old people, we're talking about an average of around 55 years or younger (according to ). I'm not saying there is absolutely no adaption, but I don't expect the effect of the adaption to be much. Nil Einne (talk) 08:12, 23 November 2008 (UTC)


 * First how do you get such low effect for an older caregiver even discounting that a parent might die? The job of bringing up children is shared round and depends on older people. That's how humans managed to reproduce so quickly. Secondly cancer does affect people of fifty and an average of 55 includes quite a few older people. Plus how did humans get to defer cancer so long except by evolution? I'm not at all certain people in the past suffered so many other diseases as are prevalent nowadays. Where did you get the business of an older person's chance of dying being as low as 1 in a million if the effect can be demonstrated easily on rats? What I was saying is it probably would have had to have affect ed about 1 in 10000 to have a strong effect and that seems quite possible to me given the rates of colon cancer and scorched food being the main new thing people ate. Dmcq (talk) 11:10, 23 November 2008 (UTC)


 * Well, in normal dosages a 1 in a million risk of cancer wouldn't be detectable in animal studies. That's why they give rats megadoses.  That will increase both the rate and the speed of cancer from any carcinogen.  As for people past reproductive age helping their descendants survive, there is some effect there, but they also consume resources that could otherwise be used by those descendants.  I would argue that our natural lifespan (which is limited by factors like cancer) evolved based on when, in prehistoric days, the genetic cost of keeping the elderly alive surpassed the genetic benefit.  Also note that in a tribal society with extended family groups, there is rarely a lack of caregivers to raise the young.  That's more of a problem with the modern nuclear family.  StuRat (talk) 17:07, 23 November 2008 (UTC)