Wikipedia:Reference desk/Archives/Science/2012 September 17

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September 17

Electron magnetic field

If an electron has no size, how does it have a magnetic north and south? Bubba73 ^{You talkin' to me?} 04:13, 17 September 2012 (UTC)

Because it has a spin, and thus an axis of spin, and thus directionality. --Jayron32 04:17, 17 September 2012 (UTC)

OK, and that spin is not the same as classical spin, right? Because you can't tell if a point is spinning (in fact it doesn't make sense for a point to be spinning). Bubba73 ^{You talkin' to me?} 04:23, 17 September 2012 (UTC)

Yes and no. It is not "Classical" spin, in that there is no internal structure to an elementary particle, so there is nothing to "rotate". Nonetheless, it is a fundemental form of angular momentum, and it does impart the sort of properties onto a particle that one would expect it to have if it did have an internal structure which could spin classically. Think of it as a quack without a duck... --Jayron32 04:32, 17 September 2012 (UTC)

Eyes without a face. Gzuckier (talk) 04:48, 17 September 2012 (UTC)

I could ask "then how does it have angular momentum if it has no size" - but I won't. Bubba73 ^{You talkin' to me?} 05:04, 17 September 2012 (UTC)

Well, the answer is it does. If you really want to understand how physics works on the "fundemental particle" level, you need to divorce yourself from what you experience with your senses. That is, don't try to logic yourself out of the existance of things which do exist, but which don't make sense on the "big world" level. Fundemental particles don't exist as little balls, even little balls with no dimensions; the most accurate models don't even treat them as discrete objects in that way. Its just there is this property of all fundemental particles that behaves as one would expect "rotation" or "spinning" to behave if the particles were, say, a basketball. Except they aren't, but the property still exists. We call it spin, but there isn't anything to spin. That is, it is spinning without anything that spins. It shouldn't be any harder to grasp than waves that vibrate without anything to vibrate in (i.e. the wave model of light), and yet we're happy to accept light as waves that don't vibrate anything. Same deal here. Just as you can have a wave that doesn't vibrate any substance, you can have a spin in an object that has no dimmensions. --Jayron32 05:31, 17 September 2012 (UTC)

Resolved

Thank you. Bubba73 ^{You talkin' to me?} 05:46, 17 September 2012 (UTC)

I wonder if it has tiny Eskimos and seals and polar bears and penguins...Gzuckier (talk) 04:50, 17 September 2012 (UTC)

Heh, this mental image of tiny people and animals sitting on electron poles is quite amusing. Thanks! :D —SeekingAnswers (reply) 14:51, 17 September 2012 (UTC)

It's just like the real north pole and it therefore does not have penguins. CambridgeBayWeather (talk) 15:34, 17 September 2012 (UTC)

If it's an anti-electron, it has negative spin. Does that mean the subatomic sun rises in the west instead of the east, or that penguins are at the north pole instead of south? I'm concerned because the lighting-variation and/or penguining could interfere with an important research project. DMacks (talk) 20:49, 18 September 2012 (UTC)

• I think that saying an electron has no size is absurd. It is fuzzy with about a Compton radius. See Rydberg atom, where electrons dutifully orbit macroscopically just like Bohr described. The electron is a little cloud of probability density, and while you don't have any good way to grab a piece of it and feel it spinning about its center, I don't know of any reason why you can't think of it actually doing that. Wnt (talk) 15:45, 17 September 2012 (UTC)
  • Well sure, that's based on defining the electron based on the laws of Classical mechanics. It's a fine model, but we've discovered a whole shitload of physics since then. --Jayron32 17:59, 17 September 2012 (UTC)
    • I'm sure I saw a report in Nature, at some point or another, demonstrating that the electrons in highly excited states (30 or so) could actually be visualized as blobs far away from the nucleus, but I'm having trouble finding it at the moment... Wnt (talk) 21:59, 17 September 2012 (UTC)
      • There's lots of ways you can visualize an electron. It depends mostly to what end you are using your model. Different models serve different purposes. --Jayron32 03:59, 18 September 2012 (UTC)

Hmmm, found something: Rydberg ionization spectroscopy: "As the electron is promoted to higher energy levels, the spatial excursion of the electron from the ionic core increases and the system is more like the Bohr model picture." Wnt (talk) 06:03, 18 September 2012 (UTC)

Someone above said "then how does it have angular momentum if it has no size". Maybe it's the other way around? everything we know has angular momemntum AND size, it's like when people thought that "cold" was a thing, not the lack of it. Like if you touch ice, it feels like the cold is going into your fingers, not that heat is being sapped out. It makes sense to our senses, but it's not really a great interpretation of reality. Vespine (talk) 22:28, 17 September 2012 (UTC)

Electrons have no size?! O_o my life was a lie! Asmrulz (talk) 20:38, 18 September 2012 (UTC)

Have there ever been any surrogate mothers over 70 in India?

Have there ever been any surrogate mothers over 70 in India? Neptunekh2 (talk) 05:17, 17 September 2012 (UTC)

According to Pregnancy over age 50 there have been two women in India who have given birth past their 70th birthday, but both before their 71st birthday, so that depends on what you mean by "over 70". --Jayron32 05:26, 17 September 2012 (UTC)

This is a bizarre question. Neptunekh2, are you sure you understand what a surrogate mother is? Or are you asking whether any woman over 70 has used another woman as a surrogate mother? Looie496 (talk) 06:22, 17 September 2012 (UTC)

Has any woman over 70 has used another woman as a surrogate mother That's what I mean to ask.

Has any woman over 70 used a surrogate mother? It wouldn't be unreasonable, particularly since surrogacy doesn't require genetic material from the social mother. That sort of info is harder to track down, though, as "someone who didn't deliver a baby" isn't terribly remarkable from a records-keeping standpoint. There's a good chance that some rich person who wants an heir has done it at some point. On the other hand, if we ask whether any woman over 70 has been a surrogate... well, per Jayron's comment above, there are two cases of Indian women who, at 70, gave birth to children conceived with donor eggs. Since they intended to keep the children themselves, though, I'd think the bigger question is whether that constitutes surrogacy. — Lomn 18:07, 17 September 2012 (UTC)

Circuits problem

How would I go about solving the following Q ?

A) You are given three resistors: two 4Ω resistors and one 6Ω resistor. Given that each individual resistor can dissipate up to 1 watt of power before burning up, how much total power in watts (W) can the smallest-valued composite resistor dissipate before burning up?

I know p = iv = i²r = v²/r, but I don't know either i or v. I can't seem to figure this out; I must be missing something obvious. Any hints ?

StuRat (talk) 07:11, 17 September 2012 (UTC)

First, find the value of the "smallest-valued composite resistor", basically all three resistors in parallel.

$R_{\mathrm {total} }={\frac {1}{{\frac {1}{R_{1}}}+{\frac {1}{R_{2}}}+{\frac {1}{R_{3}}}}}={\frac {1}{{\frac {1}{4}}+{\frac {1}{4}}+{\frac {1}{6}}}}=2.67\Omega$

Let the total power be x, it follows that

$x={\frac {V^{2}}{R_{\mathrm {total} }}}={\frac {V^{2}}{2.67\Omega }}$

Rearranging and we have:

$V={\sqrt {2.67x}}$

For parallel resistors, the smallest resistor would consumer the most power, thus we have:

$1W={\frac {V^{2}}{R_{\mathrm {smallest} }}}={\frac {V^{2}}{4\Omega }}={\frac {2.67x}{4\Omega }}$

$x=1.5W$A8875 (talk) 07:41, 17 September 2012 (UTC)

Thanks, but I see a math error on the first step:

        1        
 1/4 + 1/4 + 1/6

         1         
 6/24 + 6/24 + 4/24

   1  
 16/24

 24/16 = 1.5Ω

StuRat (talk) 07:55, 17 September 2012 (UTC)

However, when I completed the problem with that correction, I got 2.67 watts, which is the correct answer. Thanks ! StuRat (talk) 08:04, 17 September 2012 (UTC)

I intentionally inserted the error to prevent you from copying down the answer without working out the problem yourself. Oh who am I kidding, I can only dream of being that clever. You're most welcome.A8875 (talk) 08:08, 17 September 2012 (UTC)

LOL. Well, you helped me with circuits and I helped you with fractions, an equitable exchange. Thanks again. StuRat (talk) 08:18, 17 September 2012 (UTC)

Resolved

Image of the universe

Is there a good scientific reason why these images of our place in the universe are cylindrical? Dismas|^(talk) 10:08, 17 September 2012 (UTC)

Probably to give a sense of what is the orientation of these bodies in 3D...--Irrational number (talk) 12:04, 17 September 2012 (UTC)

Usually images of this type have a vertical line from the discs to each object, which unambiguously shows its location in 3D (example). These don't, though, so I can't think of any reason why they should have the discs at all. -- BenRG (talk) 23:04, 17 September 2012 (UTC)

While it may not add much actual 3D information it does create an impression of 3D. Without it you'd just have points on a plane. For some objects it limits the possible positions: anything shown above the long axis of the upper ellipse has to be in the distant half of the 3D space, anything below the long axis of the bottom ellipse has to be in the half closer to you as observer so to speak (because otherwise they would fall outside the top or bottom plane of the cylinder. Ssscienccce (talk) 17:31, 20 September 2012 (UTC)

Question number 1: Other forms of carbon chemistry

After reading hypothetical types of biochemistry I have some questions, but based on personal experience here, if I list them out in one section most of them are neglected, I ask them in different sections (is that wrong? anyway, sorry if it is). My first question is as follows. Carbon is the best candidate for ET life (any life) because of its ability to form (of course with the use of other elements) giant molecules that are not (necessarily) repetitive and do not (necessarily) behave the same in different parts of them (I think that's the best way to summarize it?). Life as we know, although not entirely "made" of aminoacids, can not function without them. Could there be other types of carbon based biochemistry that use other "minor" elements, possibly making more use of halogens or metals or even semi-metals? The article gives only one example (I mean seriously? oxocarbons?) and I just want to get a bit up to date on this, I mean carbon chemistry is so diverse. Also, can the presence of aminoacids in meteors used as an evidence that if there is ET life it has a very similar chemistry to our life and thus other forms of carbon chemistry are improbable?--Irrational number (talk) 12:30, 17 September 2012 (UTC)

The root problem is that "life" is not well-defined in a way that is universally acceptable or applicable. This is discussed at length in our main article, definitions of life. It so happens that under most conditions, carbon chemistry produces the most elaborate sustaining chemical reactions; so it's common to find complexity whenever carbon is involved. If complexity is a critical constituent of your definition of life, it's a fair bet to say that carbon is very likely to participate. And, for all we have studied exotic carbon reactions, none seem more complex than those which result in organic molecules: carbon, hydrogen, nitrogen, oxygen, and a few other important elements. This is not to say that all forms of complexity involve carbon. The magnetohydrodynamics of ionized hydrogen and helium are very complicated, yet involve no carbon. Semiconductor devices can exhibit incredible properties, and they need not involve any carbon. But, of all the self-assembling complex systems we are aware of, conventional carbon-chemistry (in salt-water solution) seems the most well-suited to any commonplace definition of life. Nimur (talk) 14:18, 17 September 2012 (UTC)

To highlight one of Nimurs points: Consider the problem of things like viruses and prions. Clearly, viruses and prions are among the realm of the living; nothing purely geologic creates them; they come from the process of Life as a big concept. They are also independent in the sense that, unlike say the skin cells you slough off or something like that, they are genetically distinct from other life forms. But they are not "alive" under most definitions. So you get the apparent paradox that a virus is not alive, but it is part of life. The nice little boxes we, as humans, try to categorize things only work most of the time. Around the edges, there are plenty of cases where our nice little categories simply don't work. --Jayron32 17:57, 17 September 2012 (UTC)

.Um... prions aren't genetically distinct. They just happen to fold into different shapes, one of which convinces your own prions to become traitors and switch to the other shape. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 18:39, 17 September 2012 (UTC)

Fair enough. But prions are still part of life, but not alive, like in the same way we think of viruses. No non-biological process has ever produced a prion. --Jayron32 18:56, 17 September 2012 (UTC)

Question number 2: Silicon biochemistry

In that same article, it argues that silicon is not a good candidate, but one of the reasons it gives is a bit weird, it says that such a life must absorb O2 and release SiO2 which can make the animal choke to death (and goes on to say that temperatures must be higher than usual so that SiO2 can be in liquid from, blah blah...) but it's like we're taking a familiar C-based cell, taking out all the C's and replacing them with Si, while this is a bit flawed because biochemistry as we know it relies on the properties of Carbon, not silicon. Doesn't it require for a hypothetical Si-based life to have a different biochemistry and therefore metabolism? I mean there are many other candidates for a Silicon compound that can be released easily other than molten SiO2, like TMS (which is a good candidate if the life is partially based on Carbon too) which is volatile. Also, the article argues that if life could be silicon based, it would be in here because terrestrial planets are mainly silicon, but do we have enough examples to conclude anything?--Irrational number (talk) 12:41, 17 September 2012 (UTC)

The article actually comes up with some good reasons - while the solidity of SiO2 is surely an obstacle that can be evaded, the lack of double bond formation sounds much more serious. What isn't said there - a lack of double bonds is particularly serious because conjugated double bonds are the "wires" by which our biochemistry often transfers charge at the molecular level. Look at chlorophyll and accessory pigments like carotenoids and anthocyanins, for example, and you'll see that they have these "wires" arranged not only to serve as antennas to receive the energy in the light, but to transfer the charge around within pretty large complexes. Then the energy is transferred on plastoquinone, which uses the quinone double bond structure to take up electrons and move them around. Of course, computer designers know that silicon is not useless for making circuits and solar panels, but it's a different technology - for now very macroscopic and thus inaccessible to early evolution - and it remains to be seen how elegantly it would be used in an independent origin of life. Wnt (talk) 16:25, 17 September 2012 (UTC)

What if by some fluke, carbon, nitrogen and oxygen is only present in trace amounts, and instead the atmosphere is composed of phosphorus and sulfur gas? I imagine a superheated planet with high atmospheric pressure, where silicon sulfide is exhaled as a gas by silicon based life, and liquid deterated sulfane has replaces water. Plasmic Physics (talk) 06:48, 18 September 2012 (UTC)

The real point is not that silicon is a bad candidate for life, but that's it's a bad candidate for life resembling what we are familiar with. Someguy1221 (talk) 06:56, 18 September 2012 (UTC)

Question number 3: Cosmic Abundance

When Arguing whether or not some elements can be the base of life forms or solvents, many are eliminated from the list based on low cosmic abundance. But doesn't it assume that there is a pretty even distribution of elements in the universe? Is that a correct assumption? Also, aren't different kinds of stars likely to produce different proportions of elements? Like stars with different metallicity? Could uneven distribution of elements make other kinds of biochemistry more possible?--Irrational number (talk) 12:50, 17 September 2012 (UTC)

Actually no, the elements with fewer protons are far more common then the other elements and as expected there is an article specifically on this issue, although it isn't exactly linear and their are some interesting outliers. In general stars all function generally the same. They start out largely hydrogen and overtime convert a chunk of that to helium and lesser and lesser amounts into higher elements before dying or exploding. Chris M. (talk) 13:56, 17 September 2012 (UTC)

This is a very Drake equation-esque problem. The answer is simple, if you break it apart into constituent pieces. What is the probability that some phenomenon that meets your definition of life will develop, given a certain soup of chemical precursors? How likely is that soup to exist, given abundance curves predicted by stellar nucleosynthesis? Multiply these probabilities, and sum over all possible cases that meet your criteria, and you have your answer. We can quantitatively predict certain parts of the formula, such as the cosmic abundance of various elements, based on astrophysical observations. Other parts of the formulation are as-yet unknown: we don't have great estimates for "how likely" life will evolve in a billion years, given any set of conditions. Again, you can break that problem into sub-problems with better bounds on the probabilities; but the end-all is that we have more unknown variables in the mix, so we can't compute a definitive result. Nimur (talk) 14:33, 17 September 2012 (UTC)

Considering that there are natural objects which concentrate heavy elements, like planets, moons, comets, and asteroids, the answer is that elements are highly unevenly distributed throughout the cosmos. And, in an area with many previous supernovae, the relative abundance of heavy elements should be increased even before this concentration effect. StuRat (talk) 18:57, 17 September 2012 (UTC)

Supernovae tend to produce elements in roughly the same proportions (since it is the same process going on), so lots of supernovae in an area will just produce more metals (ie. elements heavier than helium), not different relative abundances of metals. --Tango (talk) 22:30, 17 September 2012 (UTC)

Are you sure about that ? I was under the impression that you rarely get anything heavier than iron in a normal star (and then only in the final stages). Therefore, an area which had never had anything but normal stars would be deficient in heavy elements, while one that had lots of supernovae in the past would contain quite a lot. StuRat (talk) 02:56, 18 September 2012 (UTC)

Majority of the elements heavier than iron are produced by s-process, which takes place during the final stages of the evolution of low mass stars. Ruslik_Zero 18:46, 18 September 2012 (UTC)

Sorry, I thought we were comparing many supernovae against few supernovae rather than none. An area which has had no supernovae nearby will have different relative abundances, that is true. --Tango (talk) 19:32, 19 September 2012 (UTC)

This: The Elements: Their Origin, Abundance, and Distribution, by P. A. Cox of Oxford, is one of the most fascinating and well written books I have ever read. μηδείς (talk) 02:03, 18 September 2012 (UTC)

Ajax solution successful

Referring back to this question, I finally tried squeezing the cans because they were, in fact, cardboard. I didn't even have to cut the cans.— Vchimpanzee · talk · contributions · 15:38, 17 September 2012 (UTC)

Wow, it took you 3 years to try that ? Presumably we can mark this resolved. StuRat (talk) 19:01, 17 September 2012 (UTC)

Yes. I forgot the cans were even there. But I found them and I was almost out of the newer cans.— Vchimpanzee · talk · contributions · 20:19, 19 September 2012 (UTC)

Resolved

Arabian desert

Hi,
I look on a climate map:
and I saw that from some reason the Arabian Desert is hotter than other places in the same longitude; I ask whyExx8 (talk) —Preceding undated comment added 15:53, 17 September 2012 (UTC)

I assume you mean latitude, because areas north or south of Arabia are likely to have colder temperatures. It has to do with the how the wind blows. In that band of latitude, the wind blows west to east (see Trade wind) so before getting to Arabia, the winds basically traverse the entirety of Africa (the Sahara Desert). The land doesn't cool the air as much as the water does (the cooling effect of water is due to its high heat capacity). Other areas on that same band of latitude, like India and Central America, may have lower average temperatures because the prevailing winds have long stretches of water over which they can cool the air. --Jayron32 17:52, 17 September 2012 (UTC)

The image in the trade winds link actually shows easterly winds over the Arabian peninsula. - Akamad (talk) 22:37, 17 September 2012 (UTC)

In addition to having a large land mass in the tropics and winds blowing in the proper direction, another issue is elevation. South Asia looks ripe, but the Hindu Kush and Himalaya mountains break up what might otherwise be a massive desert. Those, in turn, are the result of the plate tectonics of the Indian subcontinent ramming into Asia. The Americas, on the other hand, have both a smaller land mass in the tropics, and mountains (the Rockies and Andes), so have only small deserts.

However, note that you can get a different type of dessert desert at altitude, such as the Gobi and Atacama. StuRat (talk) 19:06, 17 September 2012 (UTC)

Indeed, but neither the Gobi or Atacama are particularly hot. The OP seems to be asking about temperatures. --Jayron32 20:04, 17 September 2012 (UTC)

Or Bombe Alaska. -- ♬ Jack of Oz ♬ ^{[your turn]} 22:16, 17 September 2012 (UTC)

thank you all very much! Exx8 (talk) —Preceding undated comment added 23:14, 17 September 2012 (UTC)

You're quite welcome. I'll mark this resolved. StuRat (talk) 02:37, 18 September 2012 (UTC)

Resolved

Has any woman over 70 has used another woman as a surrogate mother or Vice versa?That's what I mean to ask.

Duplicate question removed; see Have there ever been any surrogate mothers over 70 in India? above. — Lomn 17:57, 17 September 2012 (UTC)

molluscum contagiosum

Sorry, we can't give medical advice here. StuRat (talk) 19:47, 17 September 2012 (UTC)
can you give someone molluscum contagiosum without having any of the symptoms yourself & if so can you be treated for it so you cant pass it back to them once there treatment is complete& thanks — Preceding unsigned comment added by Ianibdecorating (talk • contribs) 19:41, 17 September 2012 (UTC)

Clostridium

Can someone point me in the direction of references which tell me which types of Clostridium would infect cats? --TammyMoet (talk) 19:49, 17 September 2012 (UTC)

You should state that our clostridium article doesn't discuss this. StuRat (talk) 19:52, 17 September 2012 (UTC)

Well, I can point you in the direction of references by suggesting that you do a Google Scholar search for feline clostridium infection. That brings up a number of papers describing various sorts of clostridium infections, but not any sort of authoritative review. Looie496 (talk) 19:58, 17 September 2012 (UTC)

Thanks both for confirming my own searches. --TammyMoet (talk) 01:40, 18 September 2012 (UTC)

Skinny gene

I've heard that scientists have recently discovered a "skinny" gene which makes it harder for some women to put on weight despite how much they eat. Could the same gene be responsible for some men finding it difficult to put on muscle mass despite working out and eating properly? Clover345 (talk) 19:56, 17 September 2012 (UTC)

There are actually dozens of genes that affect metabolic rate -- no way to tell which one you are talking about. Most of them probably wouldn't affect muscle mass gain to a great degree, if a person eats enough to allow the necessary nutrients to be available in the bloodstream. "Enough", of course, means more for a person with a high metabolic rate than for a person with a low metabolic rate. Looie496 (talk) 20:07, 17 September 2012 (UTC)

(edit conflict) Just as there's no single factor that determines weight (it's a combination of genetics, diet, physical activity, and other environmental factors), there's no single "skinny" or "fat" gene. There are combinations of genes that predispose a person toward a lighter or heavier weight, but the effect of individual genes or combinations of genes remain poorly understood. Yes, some combination of genes that causes some women to not gain weight could have the same effect in men, but the fact that genetics affect weight has been known for many decades (it's no recent discovery) and is no miracle solution for those wishing to adjust their weight upwards or downwards given the vast number of genes involved and the complexity of their interactions. —SeekingAnswers (reply) 20:16, 17 September 2012 (UTC)

Would it be possible for sentient species to be carnivores, herbivores or flyers?

Possibly possessing ability to eat grass+leaves without cooking or flight removes the need for intelligence? And pure carnivorism would severely limit a planet's intelligent species population. I believe a lack of the hunting tools being integral (claws, long teeth, etc.) foments intelligence (also foments modern warfare because ancestors had less to lose from unarmed aggression). And why aren't there any walking creatures that gets at least some energy from photosynthesis? If these things were possible what would their bodies and evolutionary history look like? 96.246.70.87 (talk) 21:26, 17 September 2012 (UTC)

There is a "walking creature", the pea aphid, which gets energy from sunlight. Our article doesn't cover it, but see Photosynthesis-like process found in insects-gadfium 22:05, 17 September 2012 (UTC)

The rest of the question is asking for pure fanciful speculation. We only have the life we see here on earth as a sample. Looking at the life we have discovered so far and extrapolating what we think might be possible has been notoriously unreliable and flawed. We just can not possibly know what is or isn't possible with our sample size of "one". Vespine (talk) 22:20, 17 September 2012 (UTC)

(ec) The argument against flying creatures becoming sapient is that heavy brains are a problem in flight, and for strict carnivores that their limbs are not going to be adaptable for tool use. Nevertheless, our article on animal intelligence notes the intelligence of cephalopods, bears, corvids, parrots, and cetaceans, particularly dolphins, the latter being obligate carnivores. I don't think we will have anything definitive to say until xenobiologists have examined intelligent life on several planets. μηδείς (talk) 22:21, 17 September 2012 (UTC)

I know that it has been suggested, following the Alex studies that African Grey Parrots may be (somewhat?) sentient. They fly, and are mostly herbivorous creatures. --Kurt Shaped Box (talk) 22:59, 17 September 2012 (UTC)

Grass is a very poor source of nutrition, which is why cows, etc., have to spend so much of their time grazing. While you could have an intelligent cow, you probably couldn't have a technologically developed cow because it wouldn't have the spare time to spend inventing things. Meat is a much more concentrated food source (animals like lions often only each once every few days). --Tango (talk) 22:41, 17 September 2012 (UTC)

Every vegetarian would beg to differ. Chimpanzees would, too; they're mostly herbivorous and don't spend all their time eating. --140.180.242.9 (talk) 02:38, 18 September 2012 (UTC)

I don't know any vegetarians who eat only grass, but cooking vegetables vastly increases the nutritional potential for humans. Dbfirs 06:24, 18 September 2012 (UTC)

Two things 1) Chimpanzees eat meat and insects as well. They hunt and eat monkeys, for example. They are omnivores. 2) Chimpanees don't eat grass, which is calorie poor and mostly undigetible cellulose. Chimpanzees eat mostly fruit, which is high in easy to digest sugar and very calorie dense. See Common_chimpanzee#Diet_and_foraging. Not every plant material is equal. What cows eat is very different from what Chimps eat. Now, Gorillas eat a lot more grasses and leaves and pith (the meaty part of woody plants), but they spend a lot more time foraging than Chimpanzees, and generally lead a less active and more sedentary lifestyle. Food source and behavior are closely related. See Gorilla#Food_and_foraging. --Jayron32 05:09, 18 September 2012 (UTC)

Intelligence seems to arise in a large part due to biological arms races. Unfortunately, much of the discussion of alien intelligence arise in the context of science fiction, so as for references....but see Sagan's Intelligent Life in the Universe (book). μηδείς (talk) 23:32, 17 September 2012 (UTC)

BTW, I think the relevant word here is sapience, not just sentience. There is little doubt most higher animals are sentient. μηδείς (talk) 23:43, 17 September 2012 (UTC)

What is the biological arms race that led to human intelligence? (warning: idle speculation) I would be suspicious of another explanation: complex patterns of environmental change. If you look at a place like the Okavango Delta (my personal favorite suspect for the cradle of several human species) you see an environment that ranges from desert to mostly submerged every year; one marked by rivers and islands and grassland and forests and bizarre salt deposits; one where fires ravage the land every year, and those less intelligent die in front of it while others follow behind it and enjoy cooked meals. I suspect many species are what might be thought of as highly intelligent under very specific circumstances, but that a multiplicity of threats and opportunities make for a more generalizable intelligence. And now humans, having thrived on drastic climate changes for so long, can scarcely help but cause them on their own. Wnt (talk) 05:59, 18 September 2012 (UTC)

It is certainly true that humans have used our intelligence to thrive in a wide variety of environments (I don't know any other complex life that can thrive in arctic tundra, tropical rainforest and deserts), but is that the pressure that caused us to evolve intelligence? Lots of animals cope with varying climates, but mostly by migration. The fact that we didn't need to migrate allowed us to develop agriculture, which freed up time for other technological developments, so it is certainly very important. It is difficult to distinguish between cause and effect, though. We can't even properly identify when behavioural modernity arose with any certainty, so trying to identify the cause is probably futile. --Tango (talk) 11:39, 18 September 2012 (UTC)

@ Wnt. Other humans. The article itself mentions intraspecific biological arms races. Not that it says much. Read Nicholas Wade's Before the Dawn. μηδείς (talk) 18:25, 18 September 2012 (UTC)

Seems like bootstrapping to me. If humans developed intelligence in a biological arms race with other humans who became intelligent -- why not squirrels? Heck, we know the squirrels are locked in a cloak-and-dagger contest to secure their caches of nuts against rivals with keen eyes and a good memory... Wnt (talk) 04:01, 19 September 2012 (UTC)

Because squirrels don't live in small 30-member warring bands, or lie to each other, or woo their mates with complex strategies, whereas the lifetime mortality rate of young males due to intergroup violence is about 30-35% for chimps and tribal humans. Read Nicholas Wade. μηδείς (talk) 17:24, 19 September 2012 (UTC)

The only thing I can think of that might play a role: while hunting requires some intelligence (see how wolves hunting in pack behave), I assume that such a basic function wouldn't offer much opportunity for developing or discovering new skills. Eating is an essential, daily requirement, changing a winning strategy could get you killed. For animals living in herds, the same applies when it comes to attacks by predators, surviving is the norm. For solitary prey however, most attacks will result in death. Adopting a different strategy doesn't effect outcome when it's worse, but a better strategy increases the survival rate. Maybe natural selection would favour predators and herds that stick to a routine, and solitary prey that are inventive, creative. Just an idea... Ssscienccce (talk) 14:48, 19 September 2012 (UTC)

An interesting idea, but what observation are you trying to explain with it? Early humans weren't solitary prey... they tended to be predators more than prey and were very social and lived in groups. --Tango (talk) 19:34, 19 September 2012 (UTC)

Ssscienccce's model would work with bears which hunt alone and Elephants which don't hunt. They both have large ranges, remember many varied resources, and are quite creative. μηδείς (talk) 01:30, 20 September 2012 (UTC)

That's the opposite of what Ssscienccce was saying - neither bears or Elephants are solitary prey, yet they are creative. --Tango (talk) 18:13, 20 September 2012 (UTC)

Not trying to explain an observation, the OP asked about other species developing intelligence, I'm just suggesting how the odds could depend on the type of species. Humans aren't exactly build as a predator, they don't have the speed to escape most predators, and a herd of them would just be an all you can eat buffet for wolves, lions, tigers etc... That may be why they needed intelligence. Ssscienccce (talk) 17:54, 20 September 2012 (UTC)

Science is all about explaining observations. Having interesting ideas isn't much help if what they predict doesn't match what we see. --Tango (talk) 18:13, 20 September 2012 (UTC)

Length of the hair under the skin

Hi, I would like to know what is the length of the hair under the average scalp of a human. thank you Exx8 (talk) —Preceding undated comment added 23:13, 17 September 2012 (UTC)

I haven't had much luck finding hair follicle length in humans, but in mice it seems to vary (sinusoidally, for some reason) over their lifetime from 250 to 1500 μm: [1]. StuRat (talk) 02:21, 18 September 2012 (UTC)

I googled "hair follicle millimeter" and this source says 3-4 mm. μηδείς (talk) 04:27, 18 September 2012 (UTC)

...which is 3000-4000 μm, for comparison. StuRat (talk) 06:05, 18 September 2012 (UTC)

A reliable secondary source PMID 21919898 indicates a range in hair follicle length of 580 μm (for vellus hair) to 3864 μm (for terminal hair) in humans (full statement: "The dimensions of the scalp hair follicle are well documented in morphometric analysis (Fig. 2). The total length (mean ± SD) of the follicle and the length of the infundibulum differ significantly in terminal (3864 ± 605 μm) and vellus hair follicles (580 ± 84 μm)."). -- Scray (talk) 12:05, 18 September 2012 (UTC)