Wikipedia:Reference desk/Archives/Science/2018 April 30

= April 30 =

why we have so long hair?
چه عامل ژنتیکی و انتخاب طبیعی باعث شده برخلاف همرده های انسان ، موی سر تا این حد رشد کند؟ the man differed from his ancient grand parents when he went cave and started to hunting. in such condition : our tail have been fallen. our foot changed shape, because of no need to go up from trees .(from Y shape) our buttocks changed shape, for long duration sitting our body hair had been lost our head hair start to grow long--for which reason? males face start to have long hair (beard)--for which reason? our face deformed; normally we became meet eating animals; too we are still eating fruits. what is the basement reason of our hair length .too our eyebrow hair growth --Akbarmohammadzade (talk) 07:21, 30 April 2018 (UTC)
 * This site has some likely sounding answers: Why does human facial and head hair continue to grow?. -- Q Chris (talk) 11:57, 30 April 2018 (UTC)
 * See also this recent RefDesk discussion. One reference from that is What is the latest theory of why humans lost their body hair? Why are we the only hairless primate? from Scientific American. Alansplodge (talk) 19:14, 30 April 2018 (UTC)
 * I stick by my "mud ape" idea from last time. This example illustrates how humans could rely on their ability to retreat safely to muddy, watery terrain (together with teamwork and spears, that is!) to get the upper hand over far more fearsome animals.  I might notice that humans wading in muddy waters wouldn't have to worry much about getting their head hair immersed, since they have to breathe... Wnt (talk) 22:06, 4 May 2018 (UTC)
 * Another theory is that body hair got almost completely lost after the beginning of upright walking with the necessity of massive perspiration. Hairs on the head were retained as an isolation for the brain, hairy armpits and groin to minimize abrasion of damp skin. Beard and chest hairs were subsequently reintroduced to protect the lungs when man moved to cold regions.
 * By the way, buttocks didn't change shape because of long sitting (apes sit the same way as we do the whole day) but because the huge (in comparison to apes') butt cheeks are apparently necessary for us bipeds to keep the torso upright when standing and to pull the legs backwards when running. Some of this to be found by Desmond Morris. 194.174.76.21 (talk) 14:35, 7 May 2018 (UTC) Marco Pagliero Berlin

how human lost his tail?

 * Not sure who is asking this, but you should know it happened long before humans. All apes are tail-less. --Lgriot (talk) 12:52, 30 April 2018 (UTC)


 * See also Human vestigiality. All humans had a tail at a point in early life. Graeme Bartlett (talk) 12:53, 30 April 2018 (UTC)
 * Indeed, see Prenatal development, which has several pictures of embroys before they lose their vestigal tails. -- Jayron 32 16:00, 30 April 2018 (UTC)

How often are all 8 planets on the same side of the sun?
How often are all 8 planets on the same side of the sun (i.e. in a 180 degree arc), when was the last time/will be the next time and are there any resonances among the planets that make it more/less likely than if there were no resonances. If things were completely independent, I believe that the answer would be 1/128th of the time (without loss of generality, assume that Mercury is the most counterclockwise in the arc, and then each of the other 7 have a 50/50 chance of being within 180 degrees clockwise of Mercury, so 1/(2^7).Naraht (talk) 14:17, 30 April 2018 (UTC)
 * Long-term predictions of the positions of the planets are not all that simple to work out; given the intricacies of an n-body problem with that many interacting bodies. As noted at the Stability of the Solar System, the movement of the planets is chaotic in the long term, as noted at Lyapunov time, the Solar System loses its useful predictability after 5 million years. -- Jayron 32 15:10, 30 April 2018 (UTC)
 * Okay, but I think Naraht is asking for a simple and approximate answer, for which the effects you note are of secondary concern. Attic Salt (talk) 15:18, 30 April 2018 (UTC)
 * Not really. Let's say (I don't have the numbers at hand, but let's make some up), that the type of orientation Naraht is talking about only happens once every 10,000,000 years by some overly simplistic calculation.  If that were the case, then such a calculation would beyond meaningless since the Solar System is chaotic on any scale larger than 5,000,000 years.  It may not be on that scale; if it's every 1000 years or so, then we could work that out.  I'm just noting the complexities of the problem.  -- Jayron 32 15:23, 30 April 2018 (UTC)
 * Well, I'm happy to learn, but 1/128th of the time is pretty often. Is there something wrong with his/her calculation? Attic Salt (talk) 15:27, 30 April 2018 (UTC)
 * 1/128th of what time? They aren't all moving at the same speed... -- Jayron 32 15:50, 30 April 2018 (UTC)
 * Regardless, it's a pointless academic discussion anyways, and I seem to have lead you all astray; it seems to happen on order of once every millenium or so; according to this the next time will be in CE 2492. -- Jayron 32 15:53, 30 April 2018 (UTC)
 * I don't see anything in that linked article that mentions "millenium or so". Perhaps we might be confused by what is meant by "how often". I suppose the calculation by Naraht is about answering what "fraction of the time" are the planets all on the same side of the Sun. That the next time this happens is what I would call a "deterministic question". Assuming the source you cit is right, and the next time it happens is in year 2492, that would, indeed, be about millennium away from now, but the alignment would then persist for a duration of time. In other words, I don't think that having to wait a while is inconsistent with the possibility that the "fraction of the time" the planets are aligned is 1/128th of the time. Attic Salt (talk) 16:28, 30 April 2018 (UTC)
 * Presumably, the longest period of time at once that could be true would be 1/2 of a Mercurial year of 87 days, which would be 43ish days.  Hypothetically, if both Mercury and Venus were aligned when the entered the same side of the sun as the other 6 planets, they would be able to squeeze in such 43 day windows 2 more times before Venus passed out of alignment. -- Jayron 32 16:37, 30 April 2018 (UTC)
 * Okay, but I don't see anything wrong with Naraht's calculation regarding what fraction of the time the planets are on the same side of the Sun. Do you? Attic Salt (talk) 17:11, 30 April 2018 (UTC)
 * 1/128th of what time period, though? It would be 1/128th of the time it takes for all 8 plants to "reset" to the same position; we'd have to do that calculation to figure out the amount of time we're talking about.  I mean, if we mean 1/128th of a year, that's every 4 months.  It doesn't happen that often.  -- Jayron 32 17:22, 30 April 2018 (UTC)
 * Well, clearly, over timescales much longer than the longest orbital period (Neptune), but shorter than the timescales over which the orbital parameters change. Attic Salt (talk) 18:33, 30 April 2018 (UTC)
 * I thought the OP's analysis was rather clever, if not entirely helpful. The duration of any one event is 44 days (half the orbital period of Mercury). I started to write a very boring orrery program to work out an approximate answer. But it was so tedious I gave up. Greglocock (talk) 10:30, 1 May 2018 (UTC)
 * Fun fact: this is called syzygy. There's a good Scrabble word. Note as stated in the article, sometimes this is used to mean an exact straight-line alignment of bodies (such as occurs in an eclipse), but it can also be used more generally to mean when all the planets in the Solar System are on the same side of the Sun. --47.146.63.87 (talk) 22:34, 30 April 2018 (UTC)
 * Unfortunately, a standard English Scrabble set contains only two y's. Deor (talk) 16:34, 1 May 2018 (UTC)
 * And two blanks, which make it possibly to spell "syzygy", using one of the blanks for one of the ys -- Jayron 32 16:38, 1 May 2018 (UTC)
 * A word like aqueous seems rather more useful. Wnt (talk) 01:43, 2 May 2018 (UTC)
 * I like Naraht's idea of estimating the proportion of time that this condition holds, but I think that that's an underestimate because having Mercury most counter-clockwise doesn't include all possible combinations. Imagine an arc defined by ±90o around bisector of the (smaller) angle Mecury-Sun-Venus. This 180oC arc always includes both Mercury and Venus, then has a 1/(2^6)=1/64 chance of also including the other 6 planets. I think that even this is an underestimate of the proportion of time the 180o condition holds. As others have noted this doesn't help to determine the next time it will happen, but it's an interesting question by itself. Klbrain (talk) 23:27, 1 May 2018 (UTC)
 * Your probability is missing a factor 8. For each planet x, the chance that all the other 7 planets are within 180 degrees clockwise of x is 1/27 = 1/128. The 8 cases are mutually exclusive so the chance that at least one of them is happening at a given time is 8 × 1/128 = 1/16. A Monte Carlo simulation with 108 random constellations gave me 1/16.002. The longest possible duration of such an event is slightly longer than a Mercury orbit of 87.97 days. The planets rotate in the same direction. If all 8 planets are lined up exactly at some time then they are within 180 degrees from around 44 days earlier to around 44 days later. PrimeHunter (talk) 23:29, 1 May 2018 (UTC)
 * I think that I am, the Mercury is the farthest Counterclockwise is a case, but not all...Naraht (talk) 09:01, 2 May 2018 (UTC)
 * Last time was 07/14/10 to 09/09/10 (57 days). Last time before that was pre-2003 since the configuration of the gas planets made "everything on the same side" impossible from 12/31/2002 to 09/02/2009 (also 2/22/11 to 7/11/17). Next time is July 3 to August 30 this year (Counting Pluto doesn't change anything for as far as I checked (20/02/2002 20:02:20.02200220022002 to 2020)). Considering only Uranus and Neptune, 1993.3 is when they lapped each other essentially removing 1 planet from the odds, 87 years later in 2080.1x is the next time they're on opposite sides of the Sun making it 1/64tb of the time instead of 7/64th of the time. From 7/11/17 to 9/24/28 the gas planets allow, if it's not all on same side for 4,093 uninterrupted days it's the rock planets' fault. Also all gas planets will fit within 72.2 degrees in 2024 — the smallest in 164 years (1997 to 2161). These things will probably make the next decade a fairly good time for "all planets on the same side of the Sun." Sagittarian Milky Way (talk) 08:17, 2 May 2018 (UTC)
 * Great data! What software are you using for this?Naraht (talk) 09:01, 2 May 2018 (UTC)
 * Astrology software. Their positions are extremely good the times I've compared them with the official Jet Propulsion Laboratory (U.S. spaceprobes) ones so I think they're accurate. The version that makes it so easy to find these costs money, I don't know if I want to give free advertising. Sagittarian Milky Way (talk) 16:19, 2 May 2018 (UTC)
 * I'll happily advertise this for free. 81.155.220.223 (talk) 17:21, 3 May 2018 (UTC)

Artificially circulating blood without a heart
What makes it so difficult to circulate blood with pumps (even external to the patient) and without a heart at all? Blood pump is about something else, but recently a man in Prague survived 6 months with mechanical blood pumps. Wouldn't that be useful for some extremely ill patients? --Doroletho (talk) 15:45, 30 April 2018 (UTC)
 * Does the article artificial heart answer any of your questions? -- Jayron <b style="color:#090">32</b> 15:47, 30 April 2018 (UTC)
 * The article could benefit from some expansion around the difficulties of it. It recognizes that "A synthetic replacement for the heart remains a long-sought "holy grail" of modern medicine. " but "embodies subtleties that defy straightforward emulation" is rather a short explanation. I imagine this "subtleties" are maybe reaction to hormones and a two-way neuronal connection to the brain. --Doroletho (talk) 16:03, 30 April 2018 (UTC)
 * For any given definition of "success" there have been some successful such transplants, the AbioCor never made it out of clinical trials, but a few patients lived over a year with it. Others mentioned in the article are in various states of development and trials.  -- Jayron <b style="color:#090">32</b> 16:26, 30 April 2018 (UTC)
 * Also, the heart does not really communicate with the brain to pump. The Cardiac cycle is controlled by the heart itself, with no input from the brain, via the Cardiac pacemaker, a bundle of nerves that is part of the Electrical conduction system of the heart, which can run more-or-less independently from the central nervous system, though of course there are some feedback loops involving the Vagus nerve and the like that control things like heart rate.  -- Jayron <b style="color:#090">32</b> 16:32, 30 April 2018 (UTC)
 * I don't think that the autonomic issues is a real problem (feedback systems are fairly straighforward to implement with a pressure sensor). Rather, its damage to the blood cells as they pass through an un-natural pump undergoing un-natural motion, leading to ""pump thrombosis, and hemolysis". To reduce the thombosis, anticoagulants can be given, but they increase the risk of bleeding. Klbrain (talk) 23:42, 1 May 2018 (UTC)


 * Some things that come to mind, though I won't say for sure they apply, are: a) the intrinsic clotting pathway - essentially, blood expects to circulate in a system coated in living endothelium, and when it touches almost anything else there is a chance it will decide there is damage and a reason to clot. b) the atrium, a flexible chamber, with no valve at the rear and with just a little bit of muscle to pump, which accommodates inflowing blood while the atrioventricular valve is shut, in order to give it a way to smoothly keep moving forward and circulating so there is no water hammer effect during that time.  Note that even atrial fibrillation causes clotting and can lead to death, so a pump would have to really get that down right.  I don't know what they actually do for atria.  Also c) I wonder if the muscular contractions and fleshy valves of the heart might have an effect to minimize shear force within the blood compared to an artificial system. Wnt (talk) 13:38, 3 May 2018 (UTC)

Eastern wolf
Hello everybody! What exactly does the term lycaon in the scientific name derive from?--Neufund (talk) 18:45, 30 April 2018 (UTC)
 * The article titled Lycaon (Arcadia) may grant you some insight. Besides being the specific name of the Eastern Wolf, it is also the generic name of the African wild dog.  -- Jayron <b style="color:#090">32</b> 18:48, 30 April 2018 (UTC)
 * Note that Lycaon traces back to λύκος, which claims a Proto-Indo-European heritage. While perhaps the legend might have influenced the precise form of the scientific name, it is basically a grab bag of post hoc efforts to explain the deeds of "Wolf" as an anthropomorphic figure. Wnt (talk) 21:14, 2 May 2018 (UTC)