Wikipedia:Reference desk/Archives/Science/2014 September 27

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September 27

Can a hearing child speak properly if he is raised by deaf parents?

How do hearing children learn to speak when they may never have heard a word other than grunts from their parents? Do they have a hearing caretaker that provides speech training or something? And how do the parents know that their children can actually hear? 71.79.234.132 (talk) 00:01, 27 September 2014 (UTC)

We have an article on it: Child of deaf adult. Mingmingla (talk) 00:09, 27 September 2014 (UTC)

OR of course, but yes my cousin's husband is one such. He is much in demand as an interpreter by the police and ambulance service.

Very few children are restricted to hearing only their parents, so a child with normal hearing and deaf parents will hear plenty of talking from other people. They learn speech pretty normally that way. These days, of course, the ubiquitous television plays a role too. HiLo48 (talk) 22:10, 27 September 2014 (UTC)

I've heard that children's dialect/accent owes more to their peers than to their parents. (If so, in Lost it made no sense that Walt spoke American rather than Australian.) —Tamfang (talk) 08:46, 1 October 2014 (UTC)

What happens to the energy produced in respiration?

What happens to the energy produced in respiration? I'm especially interested in the brain. How does the brain use energy? Where does the energy go? 49.183.204.196 (talk) 10:40, 27 September 2014 (UTC)

Do you mean the physical process of respiration? If so, the heat produced by the muscles involved in respiration is dispersed round the body and, if it is not needed, flows to the atmosphere via perspiration etc. Our article on the brain includes a section on metabolism though it gives only an outline. The energy consumed by the brain is also largely dispersed as heat. Dbfirs 11:43, 27 September 2014 (UTC)

Can the energy be converted into light for use in photosynthesis? Or otherwise converting the carbon dioxide and water back into oxygen and glucose? 49.183.204.196 (talk) 12:21, 27 September 2014 (UTC)

I can't think of any process within the body that could turn heat into light. The liver and kidneys do synthesise glucose, but I think they need more than just carbon dioxide and water. Dbfirs 12:32, 27 September 2014 (UTC)

Of course, other plants and animals are bioluminescent, meaning they convert energy into light. For example, a firefly. However, the amount of light produced is very little, and you couldn't do photosynthesis with that tiny amount. (You can tell how much brighter sunlight is because you can't even see bioluminescence in full sunlight.) StuRat (talk) 19:41, 27 September 2014 (UTC)

Why is the amount of light produced very little? Energy is conserved. Why can't you use the energy generated by respiration to power photosynthesis or otherwise turn the carbon dioxide and water back into glucose and oxygen? 49.183.204.196 (talk) 21:38, 27 September 2014 (UTC)

Let me clarify the Conservation of Energy law. While the total amount of energy is the same (except for some theoretical cases where it's converted into mass), when any conversion of energy forms takes place, some of the energy is converted into heat, and heat can not be converted back into other forms of energy (although large differences in temperature can create other forms of energy, as in a Carnot engine). Most energy conversion processes are quite inefficient in this respect, so converting energy back and forth eventually gives you nothing but widely distributed waste heat. StuRat (talk) 06:09, 28 September 2014 (UTC)

The second law of thermodynamics says that entropy can never decrease in an isolated system, but is it not possible to create a system where entropy stays the same? 49.183.204.196 (talk) 11:14, 28 September 2014 (UTC)

Theoretically, yes, but practically, no, at least not where there's friction, resistance, etc.. An exception might be possible with superfluidity, superconductivity, etc. StuRat (talk) 23:12, 28 September 2014 (UTC)

BTW, I believe there is some micro-organism that basically behaves as a plant during the daylight, using photosynthesis to produce energy, then turns into an animal at night, burning that stored energy. Does anyone remember the name ? StuRat (talk) 06:12, 28 September 2014 (UTC)

It depends what you mean by respiration. Are you asking about Respiration (physiology) or Cellular respiration? The only fuel the brain uses is glucose see [1]. The energy it gets from this is used to produce electrical energy which powers the brain's processes and the excess is lost as heat. Richerman (talk) 14:33, 27 September 2014 (UTC)

As far as where the energy goes, much of it eventually turns into heat, which then dissipates into the person's environment. This is why we tend to be warmer than our surroundings. StuRat (talk) 19:37, 27 September 2014 (UTC)

Er, not really. Our bodies are designed to run at around 37°C which may be warmer or cooler than the surrounding environment. If that doesn't happen we're soon in in deep trouble. Richerman (talk) 21:13, 27 September 2014 (UTC)

Let me explain further. Most people are uncomfortably hot in places that are at our body temperature (with an exception for when in water, which can dissipate body heat more quickly). The reason for this is that our normal metabolic processes create heat, and if we start out in an environment already at our target body temp, that extra heat would make us overheat, or at least sweat profusely to cool down by evaporative cooling. This is why we prefer cooler temps than our body temp, or, looking at it the other way around, "This is why we tend to be warmer than our surroundings". StuRat (talk) 00:24, 28 September 2014 (UTC)

Temperatures significantly above body temperature will cause the body to absorb heat from its surroundings, and cause hyperthermia. The laws of physics are a mean bitch, and since heat cannot flow spontaneously from cooler temperatures towards warmer temperatures, people cannot maintain physiologic body temperature in an environment where the ambient temperature is above physiologic body temperature. --Jayron32 00:41, 29 September 2014 (UTC)

That's true at 100% relative humidity, but evaporative cooling can allow people to survive at temps significantly above body temp, provided they have a water supply, low humidity, and perhaps some wind to help the evaporation process along. StuRat (talk) 01:05, 29 September 2014 (UTC)

Mushrooms with holes

What's going on with these mushrooms? They look like someone has been drilling into the tops. They are right outside my workshop, but I don't think I am that careless! SpinningSpark 11:21, 27 September 2014 (UTC)

Slugs? Thincat (talk) 11:28, 27 September 2014 (UTC)

Have you observed other mushrooms like them, except without holes, in the vicinity of your workshop? Nyttend (talk) 13:27, 27 September 2014 (UTC)

Yep, definitely slugs. I saw one just like that the other day with a large slug sitting on it eating away. Richerman (talk) 14:03, 27 September 2014 (UTC)

Climate Change

One quick one...why hasn't this article addressed the recently published findings by the National Academy of Science, through the Federal study by the National Oceanic and Atmospheric Administration, in conjunction with the University of Washington?

Many people say that "Wikipedia" is left-biased, and although I defend you, it is becoming more difficult when differing scientific opinions are dismissed completely.

Thank you 50.158.98.69 (talk) 14:00, 27 September 2014 (UTC)

Which findings? And WP:SOFIXIT. DuncanHill (talk) 14:02, 27 September 2014 (UTC)

The fact that recent findings haven't been added yet doesn't mean they've been dismissed - it just means they haven't been added yet. Now's your chance to add something useful to the encyclopedia anyone can edit. And I don't think people on the left wing of politics are any more likely to disbelieve that climate change is happening than those who lean towards the centre or the right are they? Richerman (talk) 14:09, 27 September 2014 (UTC)

A better place to discuss this would be on the Talk page for the article at Talk:Climate change. But it would be nice if you could give us a link to this publication so that we have at least a rough idea of what you're talking about.

As you might expect, there have been a lot of contentious debates about the Climate change article - and it's currently under discretionary sanctions from the ArbCom folks (meaning that people had better behave themselves there - or retribution will be swift!). As far as I can see, nobody has yet added a reference like that to the article - so it's not like there is some kind of active suppression of this information. You'd (perhaps) have grounds for complaint if it had been inserted, and then deleted again without good cause.

Right now, I think you should carefully ensure that the article you're planning on 'addressing' meets Wikipedia's guidelines for "reliable sources", and if you're sure that it does, go ahead and change the article. If you're not 100% sure (especially given that ArbCom are watching) - then you should perhaps discuss it first on the Talk page...and, I'd strongly advise you to follow the "assume good faith" rule and not start off by accusing the people who work on that article of being biassed! That's a fairly insulting thing to say here - and the Wikipedia rule that you assume people are behaving in a nice way (until proven otherwise) is essential in this kind of matter. So it would be better to assume that the paper you're talking about simply didn't get noticed by them - or was rejected for solid reasons - rather than charging in and proclaiming bias, as you've already done here.

Ordinarily, a little slip in your assumption-of-good-faith would go unnoticed - but because that article is on a hair-trigger (and for good reason), I advise you to tread gently and to be as polite and assuming-of-good-faith as you can manage!

SteveBaker (talk) 14:39, 27 September 2014 (UTC)

It may have something to do with this, although I can't see at first glance how this would would impact on the climate change article. Mikenorton (talk) 16:07, 27 September 2014 (UTC)

That workshop looks quite technical to me, and at first and second glance does not contain much that would affect our current articles. I certainly found nothing that seems to conflict with my high-level understanding. --Stephan Schulz (talk) 17:25, 27 September 2014 (UTC)

More to the point perhaps, the title and content suggest that if anything, info from there is more likely to lead what the OP would call a left wing bias and not demonstrate it by excluding it. I think the OP is more likely referring to [2]. My uninfotmed thoughts are 1) It was published in PNAS but as with all such articles it's simply the peer reviewed work of the authors not the findings on the NAS. (I suspected this.) 2) It's simply a single recent article, peer reviewed sure, but as with all such things on both sides, needs to be used with care compared to more established stuff from reviews or at least studys which have become well accepted etc. 3) It hasn't even been published now (although accepted) it's even more silly to get worked up about it not being currently used. Nil Einne (talk) 16:45, 30 September 2014 (UTC)

Climate change is a significant political issue along the left/right divide only in the United States so this may be a good opportunity to point out that this website is not the Yankopedia. Roger (Dodger67) (talk) 16:14, 28 September 2014 (UTC)

scale of climate belts

Hi,
I wonder why the climate belts' scale is constant, and why it is what it is.
I mean, why one year can't the northern belt reach the equator? what prevents it?
Exx8 (talk) 16:59, 27 September 2014 (UTC)

1) Sunlight hits the tropics more or less straight on, while near the poles it hits at a shallow angle. This means much less light hits there, and as a result, there's much less solar heating. See insolation.

2) Ice at the poles exaggerates the above effect, by reflecting most of the little sunlight they get.

3) Heat can move around a bit, in the atmosphere and oceans. But most of the heat in the atmosphere moves around parallel to the equator. If you look at Jupiter's cloud bands, it's more visible there. The rotation of the planet causes this.

4) So, the atmosphere doesn't move much heat away from the equator, but the oceans do. See the Gulf Stream for one example. (I believe, in the absence of land, water currents would continue to move parallel to the equator, just as air currents do.)

5) The atmosphere can also be redirected, at times, by the jet stream. So, when it gets a kink in it, heat may be directed away from the equator, or cold air away from the poles. StuRat (talk) 17:09, 27 September 2014 (UTC)

Even in the absence of land the currents wouldn't go parallel to the equator but form cells because of the Coriolis effect. The great red spot on Jupiter is probably one of these. Dmcq (talk)

Well, the primary direction is still East-West on Jupiter, and I'm sure it would be in our oceans, too, if the path wasn't blocked. StuRat (talk) 19:21, 27 September 2014 (UTC)

Is it possible for a camera to take photos in low light conditions without image noise

Even the most expensive and advanced digital camera still produces Image noise in low light conditions. My friend bought a $2,000 digital camera and it still has image noise in low light conditions. My question is this a physical inevitability or is it a technological limitation and with sufficiently advanced technology, cameras in the future will not have this problem? ScienceApe (talk) 18:53, 27 September 2014 (UTC)

It's a technology/price limitation. I believe astronomers have cameras that can detect a single photon, and record them over time to build up a complete image. Noise on those would make them useless. Apparently either $2000 isn't enough, or he got ripped off. StuRat (talk) 19:25, 27 September 2014 (UTC)

See (Digital camera ISO speed and exposure index) and F-number. As far as "future technology" is concerned, in theory it is a matter of recording photons hits and sorting out the signal from the noise. 71.20.250.51 (talk) 19:59, 27 September 2014 (UTC)

Concerning the practical example, (using current technology) presumably the expensive camera has a decent max ISO; buying a lens specifically for low light photos might be a solution (i.e.: f/1.2 lens). 71.20.250.51 (talk) 20:06, 27 September 2014 (UTC)

As an old film photographer who has made many interesting photos with l-o-n-g exposures in low light conditions:, I wonder if a time exposure similarly allow integration of light over a period of seconds or minutes in a digital camera? Edison (talk) 20:48, 27 September 2014 (UTC)

Yes. Of course that requires a tripod and a subject that doesn't move (unless a blurry subject is desired, which often makes for an interesting photo). 71.20.250.51 (talk) 21:06, 27 September 2014 (UTC)

Detecting one photon at a time when there are not many photons will still give you a noisy image. There is a limit to how much information there is in the light, and you cannot get that information if it is not there. Graeme Bartlett (talk) 21:35, 27 September 2014 (UTC)

I don't follow. A telescope on Earth can be expected to get stray photons from reflections/refractions in the atmosphere, if that's what you mean. But a telescope in space shouldn't do that much, especially when looking at a very narrow speck of space. Is this the "noise" you meant ? As for the signal, if you only get one photon at a time from a distant spiral galaxy, you should eventually be able to see the spiral shape emerge, if you collect enough photons and are able to place them in the correct location. StuRat (talk) 00:29, 28 September 2014 (UTC)

Extremely low noise cameras already exist. The problem that has to be overcome is to reduce the amplifier noise; this requires cooling the camera to extremely low temperatures. You can then take extremely long exposures at extremely high ISO settings without much noise.

In practice, it's quite easy to eliminate the noise you get using ordinary cameras when taking long exposure pictures. What you do is you take multiple exposures with shorter exposure time instead of a single, long exposure. You then combine all the individual images, but instead of simply adding up the grey values for each pixel, you take the median. This automatically removes outliers. Count Iblis (talk) 22:58, 27 September 2014 (UTC)

Back to our question, expensive hardware can help, but as with other photography, or other just about anything, there's a lot more to it. Astrophotography hints at the great mental effort require to do it well. As with just about anything. Jim.henderson (talk) 00:45, 28 September 2014 (UTC)

The lowest possible noise for any sensor is the Poisson noise, caused by the discrete nature of light. If a certain pixel receives 100 photons, for example, the Poisson noise will be 10 photons (square root of 100), which is 10% of the signal. This limitation is imposed by the laws of mathematics, and no amount of clever engineering can defeat it. The only solution is to collect more photons, for example by having a bigger lens or bigger pixels. --Bowlhover (talk) 00:56, 28 September 2014 (UTC)

As 71.20.250.51 has already pointed out, you're trying to solve the wrong problem. With DSLR's there's two separate things to consider when working at a fixed shutter speed: 1) the ISO or light sensitivity, which is a function of the sensor (or of the film, in the case of older SLR's) and 2) how "fast" the lens is, ie. f-stop, or in other words how wide you can make the aperture. Obviously a wider opening (lower f-stop) lets you shoot in lower light without having to increase the ISO. At high > 3000-ish ISO no matter how good the sensor, it's still going to look noisy, although some sensors are of course better than others, it's likely in the $2000 range that your friend has purchased a camera with a full-frame sensor, so that's probably not the issue. It's not lack of light that generates the noise, it's the fact that you're increasing the sensitivity of the sensor that's the problem, since you're picking up more stray light. Basically it's a signal-to-noise problem. If you're trying to shoot in near darkness, and don't want a noisy image, either get a fast lens (f < 1.8) which can be pricey, or increase the exposure time, the later option being the more cost effective since it only requires purchasing a small tripod (and probably a remote trigger) to keep the camera stationary until the exposure is complete, that way you can shoot at a low ISO and just keep collecting light until you have an adequate exposure. Never crank the ISO higher than it needs to be, or your image will be noisy. I would suggest that the OP's friend, having just invested in a $2000 camera body should probably also read up on the fundamentals of photography. (+)H₃N-Protein\Chemist-CO₂(-) 13:28, 28 September 2014 (UTC)

OP's friend here. The image he is referring to is one I took of a firework on the 4th of July, with an ISO of 6400 (as it was well into night time at the time the photo was taken), a zoom lens whose F-Stop was (unfortunately) F/3.5, and a 1/640th second shutter. The noise was already controlled in the unaltered photograph (being mostly limited to the areas I didn't want the viewer to focus on), and the camera itself (A Nikon D600) had won good scores for its low noise performance even at ISOs up to that level. While the unaltered image has noise, some very basic sharpening and a touch of smoothing eradicates it, turning it into a more pleasing fine grain and produces a fine photo. Simply put, he believes "any noise is a failed photograph," even if it's grain-like noise, and despite my attempts to tell him some noise (hopefully grain as opposed to color) is inevitable in pretty much any photo you take, nothing seems to be able to sway him in the slightest. Any adjusted photo (be it even basic things like color correction) is also a "fake" photo, as it does not represent exactly what the eye sees, which is his golden standard for a good photo, and hence why any noise makes for a bad photo. That's not to say I'm not learning (still am - I think I would've tried ISO 3200 or perhaps a quicker shutter speed now), but I think that he is making the picture sound far worse than it actually is. 74.77.153.216 (talk) 16:35, 28 September 2014 (UTC)

I occasionally see that purist sort of view, though more often in discussion of audio recording. The problem is that every image recordation technology since daugerrotypes has been subject to inbuilt bias or limitation based on the system, the camera, and its reproduction process. All digital images are subject to some form of processing before we even get a chance to make our own manipulations, depending on what the engineers at Nikon, Canon or Sony have built into the imaging system to make it functional, particularly at high ISOs. For instance, Canon sensors are known to produce vivid reds, which can be an opportunity or a problem depending on one's goals. Anyone who's spent time in a darkroom will know that photography is highly subjective and malleable, which is where its potential for artistic effect is realized. Acroterion (talk) 17:37, 28 September 2014 (UTC)

Yes, that's why we need the International Commission on Illumination to try to standardize things as best as possible. Count Iblis (talk) 19:01, 28 September 2014 (UTC)

Re: remote trigger: another work around, if time is not an issue, is to set the camera for a delayed shot (2 or 10s). If you're shooting on a tripod, it will allow the shakes of pressing the button to die down before the photograph is taken, and thus reduce / eliminate blur. I did that with my Canon EOS 60D for a candlelight only shot, and it worked perfectly. The text of the book I was photographing remained perfectly legible.13:53, 28 September 2014 (UTC)

People used to hold a black page or similar very close to the lens, press the shutter, wait some seconds, and then take it away very very quickly. Sagittarian Milky Way (talk) 12:02, 29 September 2014 (UTC)

Two things. I used to shoot on ISO800 film because I actually used to LIKE the slight grain to the resulting images, (the Fujifilm 800 in particular was pretty well known for its subtle but pleasant grain). Secondly, I was interested in night time astro photography and can say that, some, perhaps not all, but a decent portion of "noise" is NOT stray light, but in fact, caused by essentially brownian motion in the CCD. You can prove this by taking long exposures with HIGH ISO in the middle of the night, with the window shades drawn, with the lens cap on, with the camera in a heavy black garbage bag, under a heavy bed sheet. etc:) You will still get a photo with noise. Vespine (talk) 06:47, 29 September 2014 (UTC)

Interesting point. You're right, I've done that with my Canon 60D. Even with the lens cap on in a shaded unlit room, there is still visible noise, so I'd have to agree that it can't be just stray light. However, CCD's are solid state, and brownian motion requires that *something* be moving diffusively in response to thermal fluctuations, so what is the "something" in this case? The only thing I can think of would be that it's light being scattered by dust, but then where does the light come from? (+)H₃N-Protein\Chemist-CO₂(-) 14:32, 29 September 2014 (UTC)

Or, were you thinking that thermal fluctuations were directly triggering excitation of the CCD? In which case the relevant process would be thermal noise. (+)H₃N-Protein\Chemist-CO₂(-) 14:34, 29 September 2014 (UTC)

Yes, it is thermal noise, which is why in professional applications where they need extremely long exposures at extremely high amplifications, they cool the sensors with liquid nitrogen or liquid helium. Count Iblis (talk) 15:22, 29 September 2014 (UTC)

Imaging the cosmic background radiation sky to WMAP precision with a CCD must be a pain in the neck... Sagittarian Milky Way (talk) 22:51, 29 September 2014 (UTC)

A low focal length (to reduce magnification) telescope is another solution. They make field flatteners too for photography with telescopes, they minify it somewhat. Sagittarian Milky Way (talk) 12:02, 29 September 2014 (UTC)

Sorry yes I accept the correction. I think I heard it once described like Brownian motion, but having just a brief look at the article it's clearly NOT Brownian motion, but thermal noise. Vespine (talk) 02:28, 1 October 2014 (UTC)

Color changing material

I've recently learnt about chemical clock phenomenon and it made me wondering whether there are any solid materials that change colour overtime.85.141.229.250 (talk) 20:06, 27 September 2014 (UTC)

Loads of them. Copper turns green over time, silver turns darker, iron turns rust-colored, bright colored paper and plastics tend to fade (although one pigment may fade faster, changing the color, too). On artificial plants, the greens tend to turn blue over time. And tattoos also lose their bright colors over time, leaving only greens and blues. White paper and bones/ivory tend to yellow over time, too. StuRat (talk) 20:44, 27 September 2014 (UTC)

Chromatophores on cuttlefish is a more interesting example. 71.20.250.51 (talk) 20:52, 27 September 2014 (UTC)

Timber fades or darkens over time, depending on the type of timber and conditions. HiLo48 (talk) 22:02, 27 September 2014 (UTC)

Metals turning colors would be due to oxidation, which would technically mean the material itself is changing, wouldn't it? ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:04, 27 September 2014 (UTC)

It's a chemical change, yes, but not always oxidation. I'd bet that most color changes relate to some chemical change within the material itself. StuRat (talk) 00:16, 28 September 2014 (UTC)

Oxidation is a "chemical change within the material itself." - Eron^Talk 20:56, 28 September 2014 (UTC)

I think he meant that oxidation is one possible chemical change that could occur, but there might be others. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:04, 28 September 2014 (UTC)

Cobalt chloride in solid form changes colour quite dramatically in response to hydration from the environment. —Quondum 17:57, 28 September 2014 (UTC)

Yes, and our cement basement floor turns from light gray to dark grey, depending on the humidity. However, this is a reversible change, so probably not what the OP meant. StuRat (talk) 19:53, 28 September 2014 (UTC)

• I think everyone above is missing the point of the question. The OP did say "solid materials that change colour overtime" -- but of course chemical clock doesn't just refer to any change over time, it refers to periodic change over time. The whole point is that it reverses itself over time, and with regularity. That is why it's called a 'clock.' (Didn't anyone look at the article before responding?!) The classic example is the BZ reaction, detailed in the article. To my knowledge, none of the examples above display periodic changes over time. The key to the periodic behavior in the BZ reaction is that it is a nonlinear dynamical system and constitutes a reaction diffusion system that is an example of an excitable medium. Theoretically, you could perhaps pour out the BZ reactants into some aerogel or agar or some other solid/porous object, and it may well continue to periodically change color. I don't think you'll be able to make a true 'solid' chemical clock. SemanticMantis (talk) 15:23, 29 September 2014 (UTC)

Can someone identify this green animal?

On this Life in green BBC page all the green animals are identified except the one at the very top, the first one you see when you get to that page. At least I can't find anything. Can you tell what it is? Thanks. Contact Basemetal here 22:27, 27 September 2014 (UTC)

Oxybelis fulgidus (aka the green vine snake or the flatbread snake). ---Sluzzelin talk 22:33, 27 September 2014 (UTC)

Wow. That was fast. Did you get it by Googling the image? I got nothing with that at first, then once (after you'd answered here) Googling the image did give me Oxybelis fulgidus, and now again it gives me nothing. Odd. Or do you just happen to know what that snake looks like? In any case, thanks. Contact Basemetal here 23:07, 27 September 2014 (UTC)

Google keeps doing it: from time to time when I Google for the image of the BBC site it finds this match and I am thus able to find out it's Oxybelis fulgidus and at other times it only returns the very BBC image I was searching for as a match and so I get nothing. And it's doing this apparently at random. I didn't know Google was so unreliable. Contact Basemetal here 23:53, 27 September 2014 (UTC)

TinEye led me to Getty Images [3]. Thanks for the question about this elegant creature! ---Sluzzelin talk 23:58, 27 September 2014 (UTC)

Allergy rates across countries

Is there any significant difference between developed countries in the level of diagnosed allergies? I remember reading somewhere that the UK has much higher rates than other rich countries, but I can't find the reference and now suspect it was just a made-up factoid. 213.205.251.92 (talk) 23:45, 27 September 2014 (UTC)

One published study said that only a few countries have credible data on allergy rates in children. Edison (talk) 00:04, 28 September 2014 (UTC)

It seems like whether a condition is a "sensitivity" or an "allergy" is subjective. That being the case, how can you come up with a meaningful comparison when different people may use different criteria to decide ? StuRat (talk) 01:10, 28 September 2014 (UTC)

It is known that indigenous people in Africa like the Hadza people have far lower allergy rates than people who live in Western countries, see e.g.. here: "One hunter-gatherer community was found to not only have a higher diversity of bacteria, but only one in 1,500 suffered from an allergy - compared with one in three in the UK.". Count Iblis (talk) 01:56, 28 September 2014 (UTC)

Right, that would be the hygiene hypothesis, but the Q was specifically about developed countries only. StuRat (talk) 05:59, 28 September 2014 (UTC)