Wikipedia:Reference desk/Archives/Science/2007 October 1

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[edit] October 1

[edit] Lightning as source of electricity

Is it possible to harvest the electricity from lightning strikes? If it is, then we can put an end to burning fossil fuel for electricity. Oidia (talk) 04:41, 1 October 2007 (UTC)

Electricity doesn't store all that well, sadly. So, if you're intending to use it all up at once -- say, launching your Delorean through time or jump-starting your monster, the I suppose lightning would work. It practice, humans just don't have a way to convert and store that much energy in that little time. Besides, you've also got to be in the right place at the right time to collect it! --Mdwyer 05:04, 1 October 2007 (UTC)
Electricity can be used for the electrolysis of water, which will produce Hydrogen, which is handy stuff to store and use energy (see Hydrogen economy). However, as Mdwyer pointed out, lightning comes in extreme bolts and it is hard to predict where it will strike, so you'd have to 'harness' it somehow. The latter can be solved by using a good lightning conductor. But then you'd have to convert all that energy into hydrogen in a split second (or could it be delayed somehow?) and for that you'd need a pretty big installation, I suppose (how big?), so that would have to be stationary, so it had better be in a place where there is a lot of lightning to be economically viable.
Btw, suppose we could somehow (by my method or otherwise) harvest all the energy in electricity. How much would that amount to? Would it be enough to fulfill all our energy needs if it were all 'harvested'? I heard on QI the other day that worldwide, there are about 200 lightning strikes per second. Stephen Fry did not say if this included minor strikes, if there are such things. The lightning article says an average lightning bolt has an energy of 500 MJ. Times 200 per second is 100 GW. Energy consumption says we use up 15 TW (2004, so probably 20 TW now). So even if we could harvest all lightning energy in the world (including in very remote places) at 100% efficiency, that would only contribute 0.5 % of our energy demand. This surprises me. I thought it would be much more. Did I make a mistake somewhere? DirkvdM 08:32, 1 October 2007 (UTC)
Apparently the idea of using lightning as an energy source is not quite as flaky as it sounds. There is a detailed discussion here and an overview article here. A company called Alternative Energy Holdings, Inc.] produced a press release last year claiming it had developed a prototype "lightning farm", but the company's website does not give an update, so practical results may not have lived up to expectations. Gandalf61 09:40, 1 October 2007 (UTC)
The real problem is that any plant that took advantage of a lightning strike - capturing and storing the energy and pushing it out onto the electrical grid - would be quite large and expensive. But how many times a year would it get struck? Even in places where the most storms are found, a handful of times at most, I'd guess. That's hardly going to be worthwhile as an investment because it's sitting idle 360 days of the year. I'm also a little skeptical about that figure of 500MJ - sure, that's the total energy of the lightning bolt - but isn't most of that consumed in ionising the air to allow the strike to reach the ground - and producing all of that light and sound energy. I always assumed that only relatively little of that actually hit the ground. SteveBaker 12:55, 1 October 2007 (UTC)
Isn't it a question of ease of collection / cost really? Surely alternatives such as solar power or wind farming would be much more economical? It does however sound like a very macho way of harvesting electricty. "We shall gather it from The Gods themselves - plucked from the heavens in my lightning-dirigible!" Don your flying goggles and scarves. Lanfear's Bane 14:06, 1 October 2007 (UTC)
I believe some places, like radio towers on top of mountains, are struck by lightning quite often, perhaps many times a month. I would expect the key would be harvesting the electrical potential before it becomes an unmanageable lightning bolt. This could perhaps be done using thin wires hanging from weather balloons, launched from mountaintops. These would pose an obvious hazard to navigation, however, so any area where this was done would have to be off-limits to airplanes. StuRat 15:03, 1 October 2007 (UTC)
Update on my calculation. The lightning article says that lightning strikes the earth only about 100 times per second (or might that difference be explained by only counting lightning striking ground, so not over sea?). But lightning between clouds is more common (doesn't say how much, nor how powerful they are). And there is also upper-atmospheric lightning. To harvest those, a solution along the lines of what StuRat says might be needed. (Possibly above the cruise altitude? Hmm, that's about 10 km I understand). But unless that lightning is much more powerful (and assuming my calculation was correct) this will even under ideal circumstances only supply a fraction of our energy needs. So unless it's real simple to develop (there is always that option, so give it some more thought), we'd better put our effort into other energy-sources. DirkvdM 07:20, 2 October 2007 (UTC)
Using airplanes isn't really going to work. Remember there is no such thing as something having a voltage - there is only 'potential difference'. It's the difference in voltage between one thing and some other thing. Unless the airplane can touch both the cloud and the ground - or one cloud and another - it can't take advantage of any difference in potential between two things. So you need a very large craft - or something trailing long cables or something. Also, lightning mostly happens in stormy weather...the very worst time to be flying! I just don't think this is a feasible idea. SteveBaker 14:33, 2 October 2007 (UTC)
I think it would fall into the same category as wind, water, and solar power, each of which are only feasible in certain places with consistently high winds, flowing water, or bright sunlight. Therefore, each can only provide a fraction of our total energy needs, but this is a good thing. We don't want to go from being overly dependent on one single energy source (fossil fuels) to another. If we used 100% solar power and the climate shifted, causing cloudier weather, for example, we would be in big trouble.
So, I think the long, thin wires trailing from weather balloons could provide some power, in certain locations (like mountaintops). Perhaps they could also be strung between mountain tops, for a system that would last a bit longer. We might even be able to adapt existing wires, like phone lines and cable-car wires, to extract some electricity. StuRat 14:47, 2 October 2007 (UTC)
Overcast skies don't affect insolation as badly as people think. It's an important factor, but not all-important. This is why solar power is even a good option in countries like the Netherlands.
Steve, of course this should not be done with airplanes. Those are real 'gas-guzzlers' that would use up way more energy than they'd collect. Balloons and electrolysis are simple enough that it might be possible to develop a cheap method of hydrogen-production that is a matter of 'let it fly and forget about it until there's enough to collect'. One problem might be that uncompressed hydrogen will make the balloon go up even further, but maybe that could be used to some advantage. Also, unattached balloons will fly off in all directions, so someone else might collect your hydrogen unless international agreements are made. DirkvdM 19:04, 2 October 2007 (UTC)

[edit] Hall of mirrors

Just curious, but has anyone ever tested the hall of mirrors in Versailles for mercury vapor? —Preceding unsigned comment added by KeeganB (talk • contribs) 15:12, 1 October 2007 (UTC)

Why? We know that mercury is used in the manufacture of mirrors. Do you think there is a problem because of the age of the mirrors - or because there are so many of them? If it's the former, I doubt that the mirrors are the original ones - when I visited there a couple of years ago, they certainly didn't have the tarnished yellowish look of very old mirrors. If it's the latter, then there are lots of places in the world with many more mirrors than that. SteveBaker 15:29, 1 October 2007 (UTC)
I haven't looked at a lot of old mirrors to be familiar with the tarnished look Steve has in mind, but I would have thought that a "yellowish look" in an old mirror was due to the use of a cheaper reflecting metal that was yellowish to begin with. (Why would the reflecting metal tarnish if it's covered with glass?) But I was in the Hall of Mirrors last week, and what I noticed was that a lot of the mirrors have a gray or cloudy appearance. I didn't take too close a look (the place was chock-full with other tourists), but I certainly assumed that they were the originals, and this coloring was introduced during manufacture. --Anonymous, 16:26 UTC, October 1, 2007.
(The reflecting metal tarnishes because only the front face of the metal is covered with glass - the back is not. SteveBaker 19:07, 1 October 2007 (UTC)
But it's the front of the metal you look at. Are you saying the metal is then enough that the tarnish penetrates its entire thickness? I didn't think of that. --Anon, 13:25 UTC, October 2.
Yep. They paint the back of the metal on modern mirrors for precisely that reason...but many antique mirrors don't have that - or the paint cracked or whatever. I just didn't recall seeing any of that kind of damage at Versailles - so I presumed that the mirrors had been replaced at some time. However, I could easily be wrong. SteveBaker 14:28, 2 October 2007 (UTC)

Don't get your panties in a wad, Stevie. I was just wondering if the possibility of dangerous levels of mercury vapor in the hall has ever been considered. —Preceding unsigned comment added by KeeganB (talk • contribs) 02:09, 2 October 2007 (UTC)

Oh - I wasn't upset. I was just wondering why you thought there might be a problem. Modern mirrors aren't a source of mercury poisoning - so I wondered whether you were concerned because of some ancient manufacturing process that I might be able to search for - or whether it was just the large number of them that might make you worry. I genuinely wanted to know the reason for your concerns in order to better answer your question. SteveBaker 14:28, 2 October 2007 (UTC)

[edit] Penis question

Is there any way of decreasing the time it takes for my penis to beome hard again after ejaculating? Thanks. —Preceding unsigned comment added by 90.240.244.96 (talk) 16:32, 1 October 2007 (UTC)

Well viagra is a popular 'hardening' drug, similar to starch but for people... ny156uk 16:35, 1 October 2007 (UTC)
First off, slow down and don't stress over it. I don't know that you are but I do know that stress is the anti-viagra. Slow down, and be intimate following ejaculation; touch, rub, fondle, do whatever turns you and your partner on. Based on my original research I'd say the erection is 80% in your mind. It comes when you are aroused, assuming you do not have a medical condition. Also it takes longer the older you get. I could keep going here but I'm not Dr. Ruth. Man It's So Loud In Here 17:20, 1 October 2007 (UTC)
Women. DirkvdM 07:31, 2 October 2007 (UTC)
Plural? SteveBaker 14:24, 2 October 2007 (UTC)
Or men or both, whatever you fancy Nil Einne 19:25, 2 October 2007 (UTC)
Hey, I see nobody has any scruples here about giving medical advice... ;-)) —Preceding unsigned comment added by 86.17.50.12 (talk) 18:39, 2 October 2007 (UTC)
I was asking a new question. It's only medical advice if they are wearing nurse uniforms. :-P SteveBaker 19:17, 2 October 2007 (UTC)
BTW, what you're asking about is Refractory period (sex) although I couldn't find anything specificically about suppressing or reducing it. Personally I think a MISLIH's advice is the best if you have a partner. Especially if you intend the relationship to be medium to long term, you may find it better for the relationship in the long run to take the time doing other things rather then trying to have the shorts refractory period possible. And if you aren't talking about a situation involving a partner well then DirkvdM's advice may be the best (reducing the time spent in one area may enable you to focus on another area). Nil Einne 19:25, 2 October 2007 (UTC)
There's a story that President Calvin Coolidge visited a farm with his wife. She nudged him and said "Cal, I hear that a rooster can do his male duty many times a day". The President said "But it is not with the same hen each time, is it?" So see the Coolidge effect, and consider the effect of changing partners, as in an orgy. Edison 05:20, 3 October 2007 (UTC)

[edit] Iridescence

Why does iridescence occur only in very thin surfaces such as soap bubbles and not in, e.g. 5 mm-thick glass? Goodgerster 18:04, 1 October 2007 (UTC)

If you have a soap bubble that's one micron thick, then 2.5 wavelengths of 400 nm blue light can fit within it, and 1.4 wavelengths of 700 nm red light can fit within it. If you have two wavelengths that are close together, like 500 nm green and 501 nm green, then the number of wavelengths will be very close (2 versus 1.996). The point is, the accumulated phase difference changes slowly with wavelength.
In contrast, if you have a 5 mm thick piece of glass, then 10,000 wavelengths of 500 nm green light fit inside, but 9980 wavelengths of 501 nm light fit inside. The difference is more than one whole wavelength, so the phase is very sensitive to the wavelength and in practice that just means it's unpredictable. The thick film has totally different effects on very close wavelengths, so they appear to average out over the whole spectrum (because your eye isn't sensitive to such tiny changes in wavelength).
In other words, a thin film modulates the spectrum by a slowly varying function (for example, stopping blue and passing red), and a thick film modulates it by a rapidly varying function that's impossible to perceive. —Keenan Pepper 18:24, 1 October 2007 (UTC)
Nice explanation. – b_jonas 09:08, 2 October 2007 (UTC)

[edit] What are the isomers for C7H16 (isomeric heptanes)?

What are the isomers for C7H16 (isomeric heptanes)? —Preceding unsigned comment added by 69.179.253.76 (talk) 19:03, 1 October 2007 (UTC)

The isomers of C7H16 are the different structures that have that formula.
Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misevaluation, but it is our policy here to not do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn how to solve such problems. Please attempt to solve the problem yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. Thank you. DMacks 19:35, 1 October 2007 (UTC)
Heptane may be of use. Algebraist 19:38, 1 October 2007 (UTC)

C7H16 is an alkane because it fits the CnH(nx2)+2 definition. So all you have to do is figure out how many structures you can create with 7 carbon atoms. Remember to look out for structures that look different on paper but bond can be rotated to give the same structure. Don't forget a linear molecule, and make sure that no C has more than 4 carbons attached to it! Good luck, have fun - I used to love these kind of questions! Aaadddaaammm 23:04, 1 October 2007 (UTC)

I could find 8, fyi. I could have missed some, though. Aaadddaaammm 00:29, 3 October 2007 (UTC)
Trust me, you don't want to know how many isomers it has. You want to know how many constitutional isomers it has. There is a big difference.
Mrdeath5493 05:30, 3 October 2007 (UTC)

[edit] "God initiated the Big Bang and then burned and died in the flames of his own creation..."

Would this statement be any less wrong than any of the other current theories about what happened just before and just after the Big Bang? --Kurt Shaped Box 19:18, 1 October 2007 (UTC)

Well, most theories of God suggest he is all-powerful and omni-present, do they not. So He should not be able to be killed, surely? I much prefer the simpler and more logical explanation: God doesn't exist. --80.229.152.246 19:45, 1 October 2007 (UTC)
  • There is currently no scientific theory describing anything "before" the Big Bang, so this is purely a philosophical question. The general idea behind objection to your theory is that the only reason to include God in the picture is that no one likes the idea of something coming from nothing. Unfortunately, you still have that problem because you start the story with God already existing; anything you can say about His provenance, one could also say about the universe's provenance, so it really doesn't buy you anything. The only reason it sounds nicer to do an end run with "God created Himself" than "the universe created itself" is that people who believe in the supernatural are sometimes willing to accept lower evidentiary standards than those who do not. --Sean 20:20, 1 October 2007 (UTC)
Speaking about something "before" the Big Bang is absurd, since current theories consider that time was created with the Big Bang. And I'd say your statement is somewhat more wrong than the other one, since yours includes God, who is completely unnecessary for the consistence of the theory. The addition of God only adds complication, making the theory, therefore, more improbable. --Taraborn 20:31, 1 October 2007 (UTC)

If time was created by the big bang, where did all the matter that is the universe come from? And if you think it came from God, what created God? —Preceding unsigned comment added by 128.101.53.147 (talk) 20:43, 1 October 2007 (UTC)

I believe the comforting part of the Judeo-Christian God is that he doesn't require a creator of his own. Someguy1221 20:49, 1 October 2007 (UTC)
How convenient! Dave 64.230.233.209 21:02, 1 October 2007 (UTC)
That's not comforting. That's infuriatingly absurd. Beekone 21:03, 1 October 2007 (UTC)
Did you miss the hint of sarcasm in there? Dave 64.230.233.209 21:09, 1 October 2007 (UTC)
It would be impossible to prove it either true or false - because no information can pass through a singularity. This makes it 'unfalsifiable' - which is a huge red flag for any theory you want science to take seriously.
It would also be impossible to disprove the statement "The tooth-fairy did it" or "Kurt the Almighty caused the initial singularity to be pooped out by his 'seagull of eternal light'" - or "A pink and purple striped hamster named Norbert created the initial singularity by running too fast on his 'hamster wheel of ultimate destiny'"...there are an infinite number of such possible statements and all of them are impossible to either prove or disprove. Why would we believe one over the other? The probability that the Christian God did it is no greater than that a Hindu god or a Roman god or a Greek god or "The Devil" or the Tooth Fairy or Norbert the ethereal hamster did it.
Worse still, all of those kinds of statement just force you to ask things like "What created Norbert?"...and when someone randomly (and without proof) says "Norbert was created by a small yellow teacup", we simply MUST ask "What created the teacup?" and when we find out who/what created THAT, we simply have another unanswerable riddle to solve. None of these complicated (and unfounded) claims are ever "final" - none has any measurable reason for being more true than the infinity of other possible creation stories. It's possible to suppose that "Norbert created the universe - and Norbert lives 'outside of time'" (whatever that means) - thereby making moot the question of what created Norbert...but why not simply say that the singularity is 'outside of time' - that's a much simpler answer.
We are typically left with two options in the case of unfalsifiable claims: Occams' Razor - which may be roughly stated as: "The simplest explanation is usually the best" and Carl Sagan's: "Extraordinary claims require extraordinary evidence" - since we have none of the latter - we'd best rule out extraordinary claims and stick with the Occam - ruling out all but the simplest explanation - which is that no weird god-like thing did the job and a simple physical explanation for the beginning of the universe is much more likely to be true.
Right now, I think the best is the one that Stephen Hawkins seems to promote - that time itself came out of the big bang, so there was no "before". Without a "before", nothing can have created the big bang - it is the first thing. To ask "what came before the beginning of time" is about as meaningful as asking what number comes after infinity. Mathematically, he could certainly be correct. But not everyone agrees with that point of view.
Another plausible suggestion is that the universe ends with a 'big crunch' as gravity pulls everything back into one gigantic black hole...the singularity of which then explodes to form the big bang of the 'next' universe. This is simple - but it's starting to look like our universe doesn't have enough dark energy/matter/whatever in it to halt the expansion - so no convenient 'big crunch' will ever happen. However, the 'previous' universes could all have had more matter/energy in them and ended in a crunch - with ours being the first to last forever.
We'll never know though.
SteveBaker 21:06, 1 October 2007 (UTC)
Be careful, Steve, or Norbert will condemn you to an eternity of hamster racing. Gandalf61 10:23, 2 October 2007 (UTC)
Trust me, I lie awake at nights fearing that very thing. :-) SteveBaker 14:23, 2 October 2007 (UTC)
In reference to God being invincible because he is all powerful: it should be noted that a necessary property of an all-powerful being would be the power of removing that power from himself. So, an all powerful being could technically commit suicide. If not, then there would be one thing which he could not do and thus he would not be all powerful. I believe the Zoroastrians had a dialog about this. I didn't see it in the article, but I'm sure they challenged several apparent properties of God.
Mrdeath5493 05:27, 3 October 2007 (UTC)
And you're assuming the concept of non-existence has any meaning to an all-powerful being. I believe, as the famously nonsensical quote goes, "There definately exists something, namely, nothing." You might say that we, in our universe, have a concept of nonexistence, but what if the entirety of the universe is the functional equivalent of a passing thought in the mind of an all powerful entity? And so our apparent concepts of existence may have no real meaning. Although, if the all powerful being can imagine it, then can't he make it...really real? I have one answer to all of this: meh. Someguy1221 06:24, 3 October 2007 (UTC)
Alright, there is a big difference between non-existence and intangibility. I think you might be equivocating the two. The phrase "nothing exists" has two meanings.
  • 1. Either there is nothing whatsoever in existence. (Which can't be true if you are discussing it), OR
  • 2. The concept of "nothing" exists.
Even if we are a passing thought in the mind of an all powerful being, there is one necessary condition of that situation: An all powerful being must exist. Otherwise we couldn't be a passing thought in his head; and, the rules still apply there too. Now, an all powerful being can do anything. So he could definitely exist while being intangible (i.e. the Christian God). However, he can't both 'not exist' and 'be all powerful'. This is because for something to have any property whatsoever, it must exist.
I believe a main theme of your statement though was how can we draw conclusions like this based on our perceptions and definitions if we have no way of verifying their ultimate truth and reliability? The answer is: it is the best we can do. Unless one of us is going to pass out of this dimension to a theoretically unquestionable position of ultimate understanding of everything, and then come back and let us know if our unique conception is reliable, then we will never know whether or not it is. Also, we can never escape the way our brains organize and conceive. So, we can never change it and can't verify it (ultimately). If you want to take the position that our perceptions might be unreliable go ahead, but then you'll never actually 'know' anything. However, most people value the type of knowledge we can arrive at through our unique understanding, so we might as well trust it until there is a reason not to. (Big correlation: this is the goal of science. We want to come as close to the perceivable truth as possible.)Mrdeath5493 18:06, 5 October 2007 (UTC)

[edit] Mix dogs

Aside from the obvious physical difficulties, is it possible to get puppies from dogs of very different sizes? Are there examples of puppies from say a great dane and a chiwawa? If it doesn't work what other characteristic would it need for them to be different species? 80.200.230.7 21:49, 1 October 2007 (UTC)

Yes - all dogs can interbreed between breeds. SteveBaker 23:05, 1 October 2007 (UTC)
Dogs are in fact all of one species, and they can therefore breed and produce fertile offspring whether they are poodles or Mexican rat terriers. In fact, the subspecies of dogs, Canis lupus familiaris falls into the same species as wolves, so dogs and wolves can actually interbreed. - Nunh-huh 23:09, 1 October 2007 (UTC)

You might find reading Poodle hybrid interesting (though as far as I know poodles can be of various sizes) ---- Xil...sist! 23:16, 1 October 2007 (UTC)

(I think this user is talking more about the obvious physical differences.) Probably only if the chiwawa is the male. . . --S.dedalus 00:10, 2 October 2007 (UTC)

There can be a problem of, well, "mechanics" when two dogs of very different sizes attempt to mate. But, I once saw a video of a small dog trying to mate with a rather annoyed-looking lioness, so anything is possible. StuRat 00:12, 2 October 2007 (UTC)

I've often wondered what the offspring of a chihuahua and a Great Dane would look like. -- JackofOz 01:05, 2 October 2007 (UTC)
Apparently others have wondered before me - Wikipedia:Reference desk/Archives/Science/2007 February 5#Dog breeds -- Help! -- JackofOz 05:53, 4 October 2007 (UTC)

The whole idea that you can divide the world's population of animals into different species, such that healthy adult individuals of appropriate sex can produce fertile offspring if and only if they are of the same species, is only an approximation. Species like dogs with a wide range of sizes are one exception. For another class of exceptions, see ring species.

Incidentally, there is an analogous problem with the idea that the different ways of speaking in the world can be divided into different languages: see dialect continuum. --Anonymous Homo sapiens speaking some sort of English, 13:37 UTC, October 2, 2007.

Artificial insemination could be used to bypass the physical problems. — Daniel 22:35, 2 October 2007 (UTC)
Only the first one. There's also the matter of the size of the puppies. Although I must admit to having no experience with how the sizes of different breeds' puppies vary. --Anon, 00:54 UTC, October 4.

[edit] Is this a new question?

If there is so many breeds of dogs, why aint there more breeds of humans? Is this a new question? —Preceding unsigned comment added by 88.109.239.189 (talk) 00:14, 2 October 2007 (UTC)

See Selective breeding --S.dedalus 00:24, 2 October 2007 (UTC)
On the first part, you've made it so, so yes it is now.
On the second part, humans almost went extinct a few million years ago (when was that again), so they started off with a very narrow gene pool. As for dedalus' answer, he means humans have pushed the limits of what one could squeeze out of the canine gene pool. Natural selection doesn't work like that. It only creates the useful varieties. DirkvdM 07:40, 2 October 2007 (UTC)
There are plenty of breeds of humans. I see groups of people at least as different from one another as, say, a German shepherd is from a Rhodesian ridgeback, and that's without even looking at different races. We're all the same species, genetically speaking, but if you ask me we're not by the taxonomical definition: Organisms are said to be of the same species if they normally interbreed. There are plenty of girls who wouldn't normally interbreed with me, and that's a fact (for the humor-impaired, that was a joke with a germ of truth in it). And I have to say that I don't think natural selection applies to humans the same way it does to the other animals. "Usefulness" of traits in humans depends on more than a trait's contribution to mere physical survival; a person's accidental resemblance to a famous person can confer advantage, for instance. Humans can alter their environment, too, allowing even those who made no contribution to altering it to survive, and we help one another survive things that would kill any animal no matter how social it was. --Milkbreath 12:37, 2 October 2007 (UTC)
I disagree - there are strong evolutionary pressures on humans - we are most definitely still evolving - check out lactose tolerance for example - we've evolved that trick over just the last few thousand years. With dogs, we intervened and things are different. There are two ways to look at what happened:
  • We deliberately bred them in ways that are contrary to evolution - often looking after dogs that could never survive in the wild in order to prevent evolution from culling the 'useless' ones that we happen to like.
...OR...
  • Dogs (like all animals) evolve to exploit the prevailing environment. In a world full of humans - with food, health-care and all other needs fully taken care of if you are a pet - it makes sense that dogs would evolve to fill the niche of being a 'pet'. If a particular kind of 'look' or temperament pleased humans then those breeds of dog got to breed on into the next generation. Breeds of dog that look terrible or bite their owners generally don't get to breed - (or at least they don't get kept as pets - so they are tossed out into a hostile environment that they aren't evolved to cope with) so they die out. In a sense, dogs are evolving to suite humans.
There is no similar pressure on humans - we evolve to suite our environment - at the same time as we are changing our environment, that's true. For there to be more than one species of human, there would have to be two different environments and very little gene interchange between the populations in those environments. With the prevelence of international travel - it's hard to imagine a population getting cut off from the rest of the world for tens of thousands of years with no genetic interchange. Sure, we're evolving - but without prolonged separate gene pools, we can't become different enough from each other to form separate species because any new gene gets stirred into the pot almost as soon as it appears. We can't build up enough genetic differences to get to the point where we can split. It's worth pointing out though - that even the more extreme differences between dogs don't yet qualify them as separate species - they can all still interbreed. SteveBaker 14:13, 2 October 2007 (UTC)
There are human gene pools that have been cut off from each other for tens of thousands of years, and birds of a feather still tend to flock together. (I'm deliberately avoiding giving examples to avoid this discussion becoming what such discussions too often do.) I'm not really saying that there are different species among humans, but only because I consider species to be defined genetically and not "culturally". Our minds can completely override any of our instincts, if instinct can indeed be said to come into play at all, and people of the most disparate genetic makeups imaginable will marry and have children, and no big deal. Certain monkeys, however, who live not far from each other, will not breed because of a slight difference in the patterns of their markings. This amounts to cultural selection. We humans have that, too, to the point where traits are selected for that confer no direct survival or reproductive benefit. If a culture selects for the ability to grow a good moustache, for instance, that culture is playing the same role in molding humans as humans do in molding dogs. --Milkbreath 16:52, 2 October 2007 (UTC)
Either I don't understand what you're saying or I don't agree. Artificial selection is different from sexual selection... Sexual selection is part of natural selection, artifical selection is not. Artifical selection is one species specifically breeding another species often without any real regard other then their what suits their requirements based on conscious thought. It means amongst other things that, artificial selection is still usually a lot faster and is goal directed. Sexual selection as it occurs in many animals including humans is only occuring within one species and is part of evolution. While it's true that sexual selection can similarly result in traits which are not directly an advantage evolutionary wise the two still aren't the same thing. Even taking into account cultural influences on sexual selection including the fact that individuals not involved directly in the reproductive event have an influence IMHO it's still useful to have the distinction (in humans obviously people like priests, leaders etc; in other animals there is probably also some influence e.g. the matriarch in elephants). I guess at the extreme of eugenics especially for example those advocates by the Nazis, it get's very hazy although even in this case, it's still within one species. (Of course if you believe some conspiracy theorists, aliens may be artificially selecting humans and some religious people who accept evolution believe God/gods are influencing us so could be said to be involved in artificial selection) Artificial selection may also have some similarities with co-evolution (although the selective pressure on humans is IMHO usually very limited) but there are still many differences IMHO Nil Einne 18:59, 2 October 2007 (UTC)
(edit conflict) My theoretical "moustache" example was not intended to be sexual selection. I didn't mean that women like the tickle, I meant that both sexes would perceive a good moustache as a desireable trait. The magnificently moustachioed would enjoy material and social advantage in additon to sexual. The male body is thus modified by selection in the same way we modifiy dogs for inessential physical characteristics. I think this would be a form of artificial selection, with culture as the agent. This is not deliberate, granted, but the result is the same. I don't want to put too fine a point on it, but I'm contending that humans have undergone a kind of de facto artificial selection within cultures, and that we have, especially recently, thwarted natural selection both positively and negatively with modern medicine and modern warfare. We're talking about breeds, not species, remember. The original question was why there aren't many breeds of human. I say there are. (And, in case you're wondering, my moustache looks like a pair of eyebrows, so I don't grow it.) --Milkbreath 19:36, 2 October 2007 (UTC)
What you are saying is of course true - but you can look at it from another direction.
  • From a human perspective: You breed a new kind of dog by getting a few litters of puppies from a different breed (or breeds) of dog - and you pick the ones that are most like what you want - and breeding from those while you neuter the others to prevent them from reproducing. From the human perspective, we artificially selected the right puppy - so this is 'artificial selection'.
  • From the dog/dog-gene's perspective: The environment the dog is evolving to fit is an unusual ecological niche where it is a parasite (or at least a symbiote) of a human family. In order to engage in this parasitic behaviour, it must not displease the humans by biting their kids - and it must meet various other arbitary criteria. Those animals that pass the test are those most likely to have offspring - classic 'survival of the fittest' where 'fittest' is defined as 'most able to reproduce in their environment'. But in the end, from a gene's point of view, this is no different to evolving to suite a new food source or to being able to hunt in a different set of weather conditions...it's just an environment that it's optimising itself to fit. The genes that most suited that environment were the ones that survived into the next generation - which is natural selection. The only unusual part is that the survival/not-survival rate is an unusually hard cut-off, so evolution happens fast. SteveBaker 19:14, 2 October 2007 (UTC)
My opinion is it's best to look at it from neither perspective. From an external perspective, one species is consciously selecting another species to achieve an outcome they desire. The second species may be 'evolving' within the environment provided by the first species but the fact that this first species has a conscious goal directed selection role is IMHO an important distinction from natural selection to most extents. The mechanisms may be the same, the outcomes may be somewhat similar to possibilies but the process has an important distinction Nil Einne 19:33, 2 October 2007 (UTC)

First, there can never be a "breed" of human because the word "breed" simply means a domesticated subspecies. So we are talking about subspecies here. In that case, there possibly has been subspecies of Homo Sapiens, including Homo Sapiens Neanderthals. As for existing subspecies, there are none that currently exist. The "races" are mostly social constructs, but there are certainly differences in skin color and facial features (like eyes) that are due to geographic distance and evolution. However these differences are not considered to be significant enough to be classified as different subspecies of Homo Sapiens. In addition to that there is a significant amount of gene flow which inhibits speciation. With airplanes, ships, etc, one can travel to the other side of the world in a short period of time. Because of this, there are no isolated groups of humans anymore, and people are free to travel and mate with anyone from any other culture if they so choose. This inhibits speciation, and thus the likely hood of subspecies arising is diminished. Malamockq 01:21, 4 October 2007 (UTC)

[edit] Locust flying speed

What is it? page does not say —Preceding unsigned comment added by 88.109.239.189 (talk) 23:38, 1 October 2007 (UTC)

~3.5 m/s or about 7.8 mph. [1]. Someguy1221 23:48, 1 October 2007 (UTC)
Note, however, that the flight speed of an individual locust is much higher than the rate of progression of a locust swarm. Each individual locust flies and then stops, and each flight is at some angle with respect to the average vector of the swarm. for example, assume that on average an individual locust spends 10% of its time flying and flies on average at an angle of 45 degrees to the average direction of the swarm. Then, the rate of progression of the swarm would be 0.1/root 2 of the flight speed of the average locust. -Arch dude 01:59, 2 October 2007 (UTC)
Swarm mechanics are much more complicated, though. Each individual's path can be thought of as a diffusion problem with a random walk. This results in a spreading swarm of ever-decreasing density. To counter that phenomenon, a "swarm" mentality exists which causes locusts to fly towards other locusts. The net motion of the swarm is a product of the random motion, as well as external stimuli such as a wind or light gradient, or the scent of food, etc. See boids for some simulations! Nimur 04:45, 2 October 2007 (UTC)