Wikipedia:Reference desk/Archives/Science/2017 July 4

= July 4 =

Is this still co-evolution?
If one species uses fancy tools to manipulate the genes of another species and the latter species is made to benefit the former species at its own expense, then is that still co-evolution? Chickens are bred to be bigger and bigger, so they are evolving. And humans are getting more food. Is this considered co-evolution? 50.4.236.254 (talk) 00:24, 4 July 2017 (UTC)


 * No, that would be selective breeding or genetic engineering. StuRat (talk) 00:27, 4 July 2017 (UTC)
 * Also see artificial selection. — Paleo  Neonate  - 06:56, 4 July 2017 (UTC)
 * "getting more food" is not evolution.
 * However, increased tolerance to alcohol, because of drinking fermented brew like beer and wine for many generations is evolution, so, you might say that Vitis vinifera and homo occidentalis (red link ?) coevolved, even-though it was all prompted by men, not by grapes.
 * Gem fr (talk) 13:39, 4 July 2017 (UTC)
 * Gem fr (talk) 13:39, 4 July 2017 (UTC)

Dating and job hunting parallels
For years, many have drawn parallels between dating and job hunting. Are they basically the same thing just with different end goals? I've seen one article mention that they are both markets with search friction. 82.132.184.18 (talk) 00:36, 4 July 2017 (UTC)
 * Including hooking up for a few years and then moving on to something else? ←Baseball Bugs What's up, Doc? carrots→ 01:31, 4 July 2017 (UTC)
 * This is probably more appropriate for the humanities reference desk. — Paleo  Neonate  - 06:54, 4 July 2017 (UTC)
 * I agree, but will nonetheless mention a few links.
 * market friction.
 * Market is such a large concept that it can be applied to pretty much everything, so why not dating and jobs? You just need to consider that girlfriend/boyfriend/husband/wife is some sort of job, while job is some sort of relationship, and voilà, they are pretty much the same, aren't they?
 * Our Matchmaking article does have a "other uses" section, related to business.
 * Our Job market article don't link to any dating related concept.
 * Gem fr (talk) 12:55, 4 July 2017 (UTC)

Eating Fish
Why people don't eat colourful fishes found in the sea? Why humans eat fish only with silver scales? And fishermen in the sea are not able to catch colorful fish. They always catch fish with silver scales in their net. — Preceding unsigned comment added by Forester7568769 (talk • contribs) 06:12, 4 July 2017 (UTC)


 * The premise of your question is wrong. Fishermen do catch more colourful fish and sell them. Here in Australia there are black, yellow or orange coloured fish for sale as well. Graeme Bartlett (talk) 06:22, 4 July 2017 (UTC)


 * How about Rainbow_trout and Salmon as food ? 06:38, 4 July 2017 (UTC)


 * People certainly do eat colo(u)rful fish, such as red grouper, red bream, parrotfish, gourami, and so on. Some fish lose their color when they die (e.g. mahi-mahi), so are not perceived as colofrul for that reason.  Some of the food fish are pelagic (scombridae. carangidae) and have countershading color scheme, whereas the most colorful fish are usually smaller tropical reef fish which are not usually used as food in the West. Hope this helps. --Dr Dima (talk) 07:04, 4 July 2017 (UTC)


 * And to the second part of your question - regarding the scales - people who do not observe kashrut do eat fish "without scales", such as catfish or eel for example. Dr Dima (talk) 07:16, 4 July 2017 (UTC)


 * Colorful fish my be aposematic, warning their would-be predators they are poisonous or otherwise unpalatable. μηδείς (talk) 17:51, 4 July 2017 (UTC)

What is this crop?
What is this crop? It won't be anything unusual - I'm simply asking because I don't know anything about agriculture.

It's in the Vienne department of France.

Hayttom (talk) 12:42, 4 July 2017 (UTC)
 * sunflower Gem fr (talk) 13:08, 4 July 2017 (UTC)


 * Thank you, Gem fr! I suppose it must be this year's crop, and nearby fields with flowering sunflowers are older.  (I hadn't compared the leaves.) Hayttom (talk) 15:14, 4 July 2017 (UTC)


 * Actually, I believe sunflowers are an annual species, and fast-growing, so I think it's likely that the less developed specimens have been planted for the same growing season, but at a significantly later date.  S n o w  let's rap 18:50, 8 July 2017 (UTC)

Tube trains and onrush of air


When waiting on an underground London Underground platform, as a hat-wearer, I'm acutely aware of the onrush of air that precedes the train's entry.

As a science ignoramus, I'm puzzled and curious that the most furious burst of air seems to end when the front of the train is still some metres away from me. I'd have thought it would increase in intensity until the train passed me. But it doesn't. I presume a well-known physical force or combination of forces is at play here. Enlighten me, but go easy, I'm a science ignoramus. --Dweller (talk) Become old fashioned! 13:35, 4 July 2017 (UTC)


 * Remember the train is slowing down as it enters the station. 79.73.134.123 (talk) 14:32, 4 July 2017 (UTC)
 * That's interesting. Logically feels right, but as a passenger, I always get the feeling they brake very late indeed. Can anyone find RS about how tube drivers brake their trains? Might vary a bit - the train stock is quite different on some lines. If relevant, I'm interested in the Northern line. --Dweller (talk) Become old fashioned! 15:30, 4 July 2017 (UTC)


 * Look at Drag (physics); the first diagram/4th image show you some line of airflow around a perpendicular plate
 * "it would increase in intensity until the train passed you" in the event that air stood completely still until directly in contact with train's head, then instantaneously pushed aside in a most violent rush. This would require air speed to go from zero (just before hit by train) to close to infinite (to instantaneously move aside and let the train take the place air at previously been), which is not possible. Hence, the process is smoother: things works quite like the train had some invisible air cushion moving with the train, that begins to push air aside quite ahead of the train, a few meters ahead. I guess this what you translate as "the most furious burst of air seems to end when the front of the train is still some meters away from me". When the train's head arrive at you level, the air has already been completely pushed aside.
 * Because underground is a tunnel, you might also be interested in piston effect and Venturi effect (the effect that push you toward the fast moving train, which will kill you if you stand too close at first).
 * Gem fr (talk) 14:42, 4 July 2017 (UTC)
 * Thanks. I'll check out those links. And you explained that really well. --Dweller (talk) Become old fashioned! 15:30, 4 July 2017 (UTC)


 * The Tube, in particular, has very close-fitting tunnels between stations, with much more space for the larger tunnels at most stations (and some stations are even bigger). The draft is mostly a 'piston effect' - the train shoves a large mass of air ahead of it, down the tunnel (because it has nowhere else to go). When it enters the station though, this is much less the case - the air can be displaced to the sides of the train instead.
 * This is noticeable on the platform near the entry tunnel. As the train approaches, even at some distance, there is a strong draft. Once the front enters the enlarged tunnel section though, this draft dissipates almost immediately - even when a non-stopping train continues through at speed, let alone when the train is also slowing to a stop. Andy Dingley (talk) 21:14, 4 July 2017 (UTC)
 * How prevalent are side walkways spoiling the tube roundness? Are 2017 Tube trains all round? I have noticed the long-distance wind effect in NY without a round train though (and a little walkway on the side of the tube) Sagittarian Milky Way (talk) 21:49, 4 July 2017 (UTC)
 * The Underground is an old and large system, so tunnels and stock vary between lines. Especially for the cut and cover sections. In the minimal tube sections though (such as the Northern Line), the tunnels are formed of circular lining segments, even if the original excavation was a bit larger and more ragged. There are no walkways, access relies on stopping services - historically they didn't run overnight. Andy Dingley (talk) 22:52, 4 July 2017 (UTC)
 * Is fit closeness limited by a desire for the doors to not be too curved, margins of safety for the train contacting the tunnel, or how much air pumping drag they're willing to accept? Are they designed to not roll easily like that model of New York subway train? Do you have an idea why NY suddenly ordered trains that roll at every track blip in the 1970s or 80s? With suspension that takes so long to dampen rolling? When even 1 person gets on you can see and feel the whole car move (not as much as when it turns or goes over a switch of course). How many meters is the longest piston effect "cylinder" in London? Sagittarian Milky Way (talk) 15:21, 5 July 2017 (UTC)
 * The deep-level tube lines were all started by private companies in the late 19th and early 20th centuries, and they chose small tunnels to keep their costs down. (Part of the Northern Line was originally built with 10'2" [310 cm] diameter tunnels! These were later enlarged to 11'8¼" [356 cm] to match other lines.) The trains were then made to fit tightly so they could carry as many passengers as possible. The fact that more of the train's energy would then be used to push air through the narrow tunnels was not considered a problem; actually it was hoped (wrongly) that this effect would make ventilation fans unnecessary. One good book I can recommend on the subject of the deep tube lines is Rails through the Clay by Desmond F. Croome and Alan A. Jackson (2nd edition, 1993, ISBN 1-85414-151-1). --76.71.5.114 (talk) 21:17, 5 July 2017 (UTC)

Number of breasts/litter size
How does the number of breasts relate to the size of offspring? The 'one-half rule' (number of mammaries equal half of litter size) seems to apply well across mammals. There are some exception though. Some animals like some moles have less breasts than 'needed'. The reason is that the youngster do not tend to fight. However, what explains too many breasts per younger? Cows have 4 breast per calf. Why? --Hofhof (talk) 13:18, 4 July 2017 (UTC)

Moved from the Humanities desk. Roger (Dodger67) (talk) 13:53, 4 July 2017 (UTC)


 * Mammary_gland, Mammary_gland
 * most of the time "why?" isn't a pertinent question regarding evolution.
 * As long as all offsprings get fed, it's not important whether they share a single breast, or have 2, 4 or more to choose from. :Now, obviously, more breast than "needed" is a safer arrangement that the reverse, so evolution certainly favors that.
 * On the other hand, "too much" is pretty neutral, evolution-wise. A 2-breasted cow just wouldn't get any edge over the normal cow.
 * Note that males have breast, usually not functional (there ARE exception of male lactation), but there, still. Why? well, why not...? Evolution didn't care to wipe them off completely, since they cost close to nothing as they are.
 * Gem fr (talk) 15:09, 4 July 2017 (UTC)


 * Some thoughts:


 * 1) Too few could definitely be a problem. Even when all working, that means the litter-mates may have to fight to get a spot (wasting energy and potentially causing injuries) and the mother may need to take longer to nurse them all, providing less time to eat and do all the other things needed to keep them all alive.


 * 2) There's also a risk that some may become non-functional for whatever reason (infection, cancer, etc.).


 * 3) Even when functional, they may become sore and the mother may refuse to nurse with those nipples. This seems like it would be particularly an issue with animals that are teething while nursing. StuRat (talk) 15:50, 4 July 2017 (UTC)


 * Pinging . -- Roger (Dodger67) (talk) 16:12, 4 July 2017 (UTC)


 * The Virginia opossum normally produces more offspring than it has teats. This is a means of natural selection via sibling rivalry, as is the fact that many viviparous sharks practice sibling cannibalism in the womb. μηδείς (talk) 18:05, 4 July 2017 (UTC)

Gorilla warfare
Chimpanzee warfare exists. What about gorilla warfare? Do gorillas ever have conflicts bigger than one-on-one, or is "gorilla warfare" always just a spelling mistake? 208.95.51.38 (talk) 16:35, 4 July 2017 (UTC)
 * Kekeke. It's guerilla warfare. μηδείς (talk) 17:44, 4 July 2017 (UTC)
 * Btw, guerilla has no relation to gorilla; it is from Spanish guerrilla (guerra +‎ -illa), diminutive of guerra ("war"), coined during the Peninsular war. — 2606:A000:4C0C:E200:65B0:9134:56E3:14CB (talk) 18:48, 4 July 2017 (UTC)
 * That is why I asked if "gorilla warfare" was always a spelling mistake. 208.95.51.38 (talk) 19:09, 4 July 2017 (UTC)
 * I thought you meant it the other way around (that geurilla was meant to be gorilla). 2606:A000:4C0C:E200:65B0:9134:56E3:14CB (talk) 19:23, 4 July 2017 (UTC)
 * It's not traditional war, but this ape went ape on the zoo-going Dallas public in broad daylight, wounding four (including a child) and alarming countless birds before confronting police and going down in a hail of bullets. In 2004, the immediate theory was that this was an isolated act of revenge, committed by someone who could no longer tolerate being enslaved, oppressed and mocked by local greater primates. In 2017, they'd take one look at the name "Jabari" and it'd be settled: probably not working directly for the WWF, but clearly poisoned by their radical online propaganda. InedibleHulk (talk) 17:53, 4 July 2017 (UTC)


 * There is an article about actual "gorilla warfare" in The Atlantic -- but I can't read it without unblocking ads:
 * — 2606:A000:4C0C:E200:65B0:9134:56E3:14CB (talk) 19:29, 4 July 2017 (UTC)
 * I've always wondered if anyone has ever trained a chimp or gorilla to shoot people with a handgun... sounds like it would be a great undergrad research project, no? ;) Wnt (talk) 22:20, 4 July 2017 (UTC)
 * What could possibly go wrong? Iapetus (talk) 09:07, 5 July 2017 (UTC)
 * You've been influenced by seeing too many scientists in films do things like making sharks extra brainy. ;-) Dmcq (talk) 15:33, 5 July 2017 (UTC)

The first humans
Is it true that all humans have the same forefather? Discovery channel said that there was a race of only 2000 humans in Africa, and they migrated to different continents.

After thousands of years they became African, European, Indian, Arab, Asian. — Preceding unsigned comment added by Luckynumberninetynine (talk • contribs) 16:36, 4 July 2017 (UTC)


 * See . Tgeorgescu (talk) 16:41, 4 July 2017 (UTC)


 * See Y-chromosomal Adam. Loraof (talk) 17:35, 4 July 2017 (UTC)


 * See Most recent common ancestor, and the section on MRCA of living humans.--Wikimedes (talk) 04:55, 5 July 2017 (UTC)
 * While we're at it: Recent African origin of modern humans and population bottleneck are relevant. As the latter article says, some have hypothesized that the human population got down to 2,000 or so at some point, but this is not universally accepted. --47.138.161.183 (talk) 06:02, 5 July 2017 (UTC)


 * 1) Our others chromosomes have no reason to come from the individual that gave us our Y
 * For instance, you and all of your brothers and sisters (if any) have 4 grandparents, and only your Y (if you are male) can be attributed to a specific individual, who may have contributed any where from zero to all of your other chromosomes (with an average 25%, that is, 11 chromosomes)
 * 2) moreover, chromosomes themselves are not stable units, they switch pieces with each other: (quote from current chromosome article, emphasis added)
 * "Gametes are produced by meiosis of a diploid germ line cell. During meiosis, the matching chromosomes of father and mother can exchange small parts of themselves (crossover), and thus create new chromosomes that are not inherited solely from either parent."
 * Bottom line: chances "that all humans have the same forefather" are 0,0000000000...001 % (zero, for all practical purpose)
 * Gem fr (talk) 12:53, 6 July 2017 (UTC)
 * Don't agree with Gem fr's bottom line. Change of a common male ancestor is 1 (that is, certain); have a look at Y-chromosomal Adam linked above, and note that the estimated date is currently about 275,000 years ago. The existence of the last common ancestor (for each and all species) was well described in Dawkin's The Ancestor's Tale.

Emergency room presentations of anxiety
Are Presentations of anxiety common in ER departments? Or do they tend to present complaining of "life threatening" symptoms which they suspect is something else? 82.132.229.246 (talk) 18:01, 4 July 2017 (UTC)


 * Anxiety does often present as symptoms like a rapid pulse, high blood pressure, flushed skin, etc., and those symptoms are shared with many other medical conditions. Also, even if the person appears to have anxiety, it can also be difficult to determine if that's a result of the physical symptoms or the cause. StuRat (talk) 20:17, 5 July 2017 (UTC)


 * There are many symptoms that are presented in medical care that are special cases of anxiety, such as "white coat syndrome." 209.149.113.5 (talk) 12:24, 6 July 2017 (UTC)