Wikipedia:Reference desk/Archives/Science/2011 June 29

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June 29

Isn't hair loss an evolutionary trait?

Is it really a health problem? I've no doubt that were it not for sexual selection, we could easily become hairless in the future. (And in case you're wondering, I've beautiful hair.) Imagine Reason (talk) 01:04, 29 June 2011 (UTC)

I think you could say that for any trait that's genetic or otherwise hereditary.

I imagine it's a very small comfort to the afflicted, though. APL (talk) 02:01, 29 June 2011 (UTC)

Is there any decent study of the different rates of hair loss among different human populations. As a mature Australian of northern European ancestry, my shiny dome seems to be becoming larger by the day, but all my Australian Aboriginal friends of similar age still have masses of wavy locks. (It seems they use the same silver hair dye as me though ;-) ) My theory is that, in an evolutionary sense, keeping one's hair for longer mattered more in the Australian sun than in the Scottish mist. Anyone got any better information than my totally original research on this small sample? HiLo48 (talk) 02:34, 29 June 2011 (UTC)

Our Baldness article does touch on a couple of studies that measured people's perception of the bald and balding, on the theory that this perception may serve a social purpose for the chrome-domed, and hence evolution and natural selection may have encouraged it. For you, that is. Comet Tuttle (talk) 03:36, 29 June 2011 (UTC)

Somewhere there is a silverback gorilla who is just aching to have access to Just for Men. --Mr.98 (talk) 03:42, 29 June 2011 (UTC)

Unexpected hair loss can be a problem, i.e. a sign of illness of some kind. However, if some of your ancestors went bald, that would increase your odds of going bald due to genetics. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:42, 29 June 2011 (UTC)

I don't know that it is a "health problem" on par with say, cancer, but it certainly can be a "quality of life" issue; if a person feels insecure about their hair loss, it can affect their quality of life in negative ways, and this is a real problem for people who are balding (and who care, I should add. There are, of course, balding people who don't give a shit). Insofar as people feel that their quality of life is diminished by hair loss, then its something that will be dealt with. Insofar as it being an "evolutionary trait", sure hair loss is an evolutionary trait, but confirming that fact is akin to confirming the fact that "green is a color" or "17 is a Prime Number". Its true, but I'm not sure that being true implies that it is also important, insofar as being bald is something that is a driving force for natural selection. Some traits are preserved in the genetic history not merely because they are advantageous, but just because they aren't disadvantageous enough to cause it never to be passed on. Since most people don't become bald until after their usually mating age (i.e. most people have their kids in their 20s and early 30s, but baldness doesn't often strike until a few years after that) would be a small bit of evidence in support of the "sexual selection" arguement, (i.e. sexual pressures push men to have a full head of hair, at least long enough to mate) though much of genetics is a complex, probabilistic situation and not strictly "X is good so exists, Y is bad so should never exist" sort of situation. Androgenic_alopecia#Hair_loss_and_genetics has some actual background on the genetic component of baldness. --Jayron32 05:46, 29 June 2011 (UTC)

Interesting link. Thanks. Imagine Reason (talk) 18:42, 29 June 2011 (UTC)

As I said in the evolution thread above, I am loath to call any common genetic variation a disease. Generally speaking, a gene variant which has existed for over tens of thousands of years, or longer, should have some merit. Now there are nuances to that where heterozygosity is involved - for example, I would argue that the sickle cell anemia gene should not be called a "disease gene" where malaria is endemic; yet sickle cell anemia is a disease; perhaps lack of that trait is also a disease when malaria is a leading cause of death - but if we can obliterate malaria from the face of the Earth, perhaps we could justly play God and say it is time for evolution to move on. But these nuances don't apply to baldness, where only one copy of the gene is affecting how men look. Any present fashion on the point is transient, without long-term significance. Otherwise... well, would you say that being black in Confederate America was a disease? Wnt (talk) 23:08, 29 June 2011 (UTC)

Antarctica without an ice sheet in the summertime?

I was watching a documentary about Antarctica a couple days ago and in it, it said that Antarctica is freezing, even in the summertime, because its ice sheet reflects the sunlight away from the land. But if Antarctica didn't have an ice sheet (and assuming the continent wouldn't be flooded from what I see from this image), approximately how hot would it be in the summertime, when the sun shines on the continent for half of the year? 64.229.6.52 (talk) 02:02, 29 June 2011 (UTC)

You can look to other locations on the antipodes from Antarctica which lack an ice sheet to get an idea. Barrow, Alaska has average daily temperatures about 10 degrees farenheit (5-6 degrees Celsius) over freezing. Tuktoyaktuk has similar temperatures. The closer you get to the poles, the colder it would get, even with several months of constant sun; the angle of insolation is so oblique that, though the sun is technically shining for months at a time, it provides very little heating. Imagine a ball thrown directly at a target, and then the same ball at the same velocity hitting the target with a very slight glancing blow. The amount of energy imparted to the target by the ball is very much tied to the angle it strikes the target at; its the same with the heating effect of the sun. BTW, you may also want to read albedo which is related to the initial presumptions about the effect of snow on the climate of Antarctica. --Jayron32 02:53, 29 June 2011 (UTC)

Should you really be using an analogy using momentum? Comet Tuttle (talk) 03:33, 29 June 2011 (UTC)

(edit conflict)Note that those figures for Barrow are the average high temperatures in the summer; the average temperature year-round is well below freezing. I suspect that the reflection of ice has some effect on the near-surface temperature; but not much, especially near the ocean. A good deal of the low temperatures in the coldest areas of Antarctica are due to it being as high as some of the highest mountains in the United States; due to adiabatic cooling, the higher you go above sea level, the colder it will be. Vostok Station, which had the coldest temperature ever recorded on the Earth's surface, is almost 3,500 metres (11,500 ft) above sea level, atop a giant ice sheet miles thick. Compare its mid-summer average temperature of (−32.1 °C (−25.8 °F)) to that of Alert, Nunavut, Canada (3.3 °C (37.9 °F)), which is further north about the same equivalent latitude in the Northern Hemisphere, but is at sea level; this is almost the exact difference you would expect for an elevation change of 3.5 kilometers.-RunningOnBrains^(talk) 03:37, 29 June 2011 (UTC)

West Antarctica without an ice sheet would be largely ocean, and this has happened as recently as the Eemian interglacial. The albedo effects of any vegetation would also be a factor. ~AH1 ^(discuss!) 01:11, 30 June 2011 (UTC)

Gases

1.many properties of gases (and other states of matter) are explained by the movement of the particles in them, but my problem is that I can't add them all together to have a general image of gas behavior. so my question is what is the difference between motions that make currence(like wind),thermal motions,mechanical motions that let the sound propagate in the gas,motions that cause the matter to make electromagnetic radiation(heat),etc.Iknow that some of them are probably the same but I want to clearify it.Thermal motions are described "random" but what is th definition of random anyway?and about mechanical waves, how can the random-moving particles suddenly oscilate in srtaight lines? is exactly that way?

2.another question I have is that if you have acloud of Ionoized gas(plasma) and make sound waves in it will the cloud propagate electromagnetic waves with exactly the same frequency because of its moving charged particles?thanks a alot.--Irrational number (talk) 07:04, 29 June 2011 (UTC)

I'm mostly unable to understand what you are trying to ask in #1, but as far as the definition of "random", see our article randomness. ~ Mesoderm (talk) 08:38, 29 June 2011 (UTC)

What I mean is what is the difference (if there is any difference) between microscopic motions that cause macroscopic phenomenon like I mentioned above (currents,heat,sound,radiation,etc).Because when I ask my teacher what is the cause of heat,sound and other effects the answer is always motions of microscopic particles.I hope you understood me (i'm not a native speaker of English, so I apologize!).Thanks in advance. — Preceding unsigned comment added by Irrational number (talk • contribs) 09:38, 29 June 2011 (UTC)

In the kinetic theory of gases the macroscopic properties of a gas (such as temperature and pressure) are related to the microscopic motions of its individual molecules. We cannot follow the individual motions of every molecule, so instead we assume these motions follow some given random distribution, and we relate the macroscopic properties to statistical averages (across time, space or population space) of these random motions. Usually the motions of the individual gas molecules are assumed to be distributed in such a way that the time average of the total momentum of the molecules is zero. But a constant wind could be modelled by adding a non-zero constant wind velocity on top of these random thermal motions, so as to give a non-zero time average. And a sound wave could be modelled by making one boundary (or wall) of the container vibrate with, say, a sinusoidal function of time, thus creating a pressure wave that propogates through the gas. In practice, it usually more feasible to study wave propogation by modelling the gas as a continuum and applying a differential equation such as the wave equation. But, in principle, all of the macroscopic phenomena that you mention could be deduced from the motions (and rotations) of individual gas molecules, if we knew them in sufficient detail. Gandalf61 (talk) 10:52, 29 June 2011 (UTC)

Try this on for size. Start with a gas with absolutely no non-random motion. That is, you have a perfectly "still" set of conditions. What you have in that case is all of the particles moving randomly, as individual particles, that is there are equal numbers of particles moving "left" and "right" so that, in the bulk material, their effect is to exactly cancel. Now, introduce a disturbance to this material, say in the form of a force acting on one end of the gas (in other words, "wind".) What happens now is that some larger fraction of the particles is now moving in one direction more often than the other; that is whereas if before 50% were moving left and 50% were moving right, say 60% are moving left and only 40% are moving right. Now you have wind. --Jayron32 18:41, 29 June 2011 (UTC)

Wave propagation works via the energy transfer from particle to particle of converted random motions, so that this energy has peaks and troughs in intensity that travel in a constant direction away from the source. ~AH1 ^(discuss!) 01:09, 30 June 2011 (UTC)

General Tau Theory

Is this real? I just looked at General Tau Theory and it seems to be nonsense to me. 78.25.219.244 (talk) 07:59, 29 June 2011 (UTC)

Looks like ramblings of a mad-man to me. Note that the one reference is a dead link and so is the external link to "Dave N. Lee". The one relevant internal link is James J. Gibson, which appears to be a proper article.

This might very well be some "new age" theory, but those don't have any scientific basis. We might remove the article, in that case, unless it's notable enough. That is, even the whacky theories of certain cults are allowed articles here, not because anyone believes that they are true, but because they are notable. StuRat (talk) 08:26, 29 June 2011 (UTC)

The criteria for "odd theories" is described at WP:FRINGE. --Mr.98 (talk) 13:47, 29 June 2011 (UTC)

Apparently, yes. [1][2][3][4][5] Provided that "real" includes a theory of motor coordination processes discussed by academics in the peer reviewed literature. Dragons flight (talk) 08:41, 29 June 2011 (UTC)

OK, in that case it needs a major rewrite, so it actually defines it's terms, like "tau" (right now it just has a link to a general discussion of the Greek letter). StuRat (talk) 13:57, 29 June 2011 (UTC)

I've fixed the links in the article - it seems to be genuine, or, at least, hosted on Edinburgh University's website. Scottish taxpayers' money gets spent on this sort of thing? Ah well... Tevildo (talk) 22:12, 29 June 2011 (UTC)

Two words define this sort of situation... "professor emeritus" I don't know why - I don't believe for a minute that it's truly an age-related effect. Rather, I think there is a complex social process by which people become marginalized and begin to seek perhaps overly innovative strategies. For that matter, I don't know if "rogue humans" can be defined biochemically. Wnt (talk) 23:12, 29 June 2011 (UTC)

All Gibsonian stuff tends to look weird to those who are unfamiliar with it, and this is no weirder than a lot of it. There don't seem to be any RS-level sources for this particular article, but Lee has a very extensive reputable publication record, including a (co-authored) paper in Nature. In short, there perhaps is not a proper basis for a Wikipedia article, but there is no call for this "ramblings of a madman" stuff. Looie496 (talk) 00:14, 30 June 2011 (UTC)

It seems to be a form of antireductionism, coupled with something related to the tau-function, which is an oscillation that seems to exponentially increase in amplitude. ~AH1 ^(discuss!) 01:06, 30 June 2011 (UTC)

No, it has nothing whatsoever to do with that. In Lee's version of motor control theory, tau is an estimate of the expected time until some event occurs. For example when a person swings a golf club, tau is the estimated time until the club comes in contact with the ball. When a person brakes a car to avoid hitting something, tau is the estimated time until collision given the current velocity (I think). Looie496 (talk) 01:38, 30 June 2011 (UTC)

That's the type of thing we need in the article, to make it more accessible. The topic doesn't seem all that complex, but the author chose to make it sound complex by inventing all those odd terms. This seems to be a common practice in academia, to make themselves seem smarter by intentionally obscuring a topic so that few people can understand it. This, of course, runs firmly against (what should be) the mission of academia, to educate the masses. StuRat (talk) 16:16, 30 June 2011 (UTC)

OK, I moved (and reworded) a paragraph to the lede, to hopefully make this article more accessible, including defining all the terms. How does it look now ? StuRat (talk) 16:48, 30 June 2011 (UTC)

Comprehensible, thanks. --Tagishsimon (talk) 16:56, 30 June 2011 (UTC)

You're welcome. StuRat (talk) 07:56, 1 July 2011 (UTC)

50%t

What is %t?Curb Chain (talk) 19:23, 29 June 2011 (UTC)

A typographical error? The "t" is directly under the "5" key on most English language keyboards, which could easily lead someone to accidently depress it when typing "shift-5" to make the % sign. It should read "a relative humidity less than 50%" --Jayron32 19:29, 29 June 2011 (UTC)

Looking at the linked source, it shouldn't make any mention of humidity because the source only discusses temperature. -- kainaw™ 19:30, 29 June 2011 (UTC)

fixed. Dauto (talk) 20:27, 29 June 2011 (UTC)

potassium and sodium in seawater

Earth's crust contains 2.6% potassium and 1.8% of sodium so this roughly the same amount. But seawater contains 0.39 g/L potassium and 10.8 g/L sodium. This is a large difference. Both elements form nearly only water soluble salts which readily dissolve in water. Only the more complex silicates retain both elements. .I read somewhere that clay minerals retain potassium better than sodium, but is this effect enough to create this large difference in seawater? A nice book as a reference would be very nice. Thanks!--Stone (talk) 21:04, 29 June 2011 (UTC)

An intriguing observation. These lecture notes go into the general problem of how the chemistry of seawater differs so much from average river water. As to potassium they say "Potassium is added to seawater by hydrothermal circulation as well as river inflow. The dominant sink is less clear but appears to be low temperature scavenging by basalts on the flanks of midocean ridges during low-temperature alteration". Given the inbalance this must be a pretty powerful sink, with the potassium eventually being returned to the continental crust during the subduction process presumably, but I'm not sure that this process has been fully supported by later observations after it was first proposed a few decades ago. I think that there is as yet no definitive answer to the question 'where does all the potassium go?'. Mikenorton (talk) 19:38, 30 June 2011 (UTC)

Low-gear torque

Hello. How can I prove that lower gears yield more torque than higher gears? Thanks in advance. --Mayfare (talk) 22:57, 29 June 2011 (UTC)

Probably by using the magnitude formula specified in the torque article. --Tagishsimon (talk) 23:07, 29 June 2011 (UTC)

• You'll also have to refine your claim. I think I know what you mean, but as-written it is false. SemanticMantis (talk) 02:24, 30 June 2011 (UTC)

This looks like a homework question. We don't do people's homework for them. However, here are some thoughts to start you thinking. A gear train can transmit energy, but it can't store energy. Therefore the work done on the input shaft must be equal to the work done on the output shaft, but the two will be rotating in opposite directions so the resultant work will be zero. When a torque T rotates through an angle A (measured in radians) the work done is TA. So the work done on the input shaft is T_iA_i and the work done on the output shaft is T_oA_o. The ratio of angles through which the input and output shafts move is related to the ratio of the number of teeth on each gear. Use this information to examine what the relationship might be between the torques on the two gears. Dolphin (t) 08:29, 30 June 2011 (UTC)

If my suggestion above is a bit complex think about this alternative way of proving it. Think of the two gears as being called A and B. A exerts a force F_A on gear B. F_A acts a distance b from the center of gear B, and so it exerts a torque b*F_A on gear B. Conversely, B exerts a force F_B on gear A. F_B acts a distance a from the center of gear A, and so it exerts a torque a*F_b on gear A. You know the relative dimensions of a and b because they are proportional to the number of teeth on the respective gear. All that remains is to establish the relationship between forces F_A and F_B. If it isn't immediately obvious what that relationship is, have a look at Newton's laws of motion to get some ideas. Dolphin (t) 07:56, 1 July 2011 (UTC)