Wikipedia:Reference desk/Archives/Science/2016 December 2

= December 2 =

Rabbit habit
Is it true that rabbits eat their own crap?--213.205.252.104 (talk) 01:45, 2 December 2016 (UTC)
 * Read Rabbit. -- Jayron 32 02:06, 2 December 2016 (UTC)
 * There is a difference between being unable to vomit, and being unable too eat their own vomit. The way the question is phrased makes it all sound rather unpleasant, though in fact the rabbit has evolved a very neat and efficient solution to the problem of getting enough nutrients from a diet that would fairly quickly kill a human. Wymspen (talk) 10:50, 2 December 2016 (UTC)
 * I was familiar with the term "pseudorumination", but apparently "caecotrophy" is of relevance. Wnt (talk) 18:53, 2 December 2016 (UTC)
 * Cecotrope is the word I know for special feces that serve a nutritive function. 19:30, 2 December 2016 (UTC)


 * Here is an article about this topic, written by a veterinarian. SemanticMantis (talk) 19:30, 2 December 2016 (UTC)
 * Strange we dont have an opinion from our very own rabbit, isnt it?213.205.252.104 (talk) 02:30, 3 December 2016 (UTC)

Identify a weapon used by the South African Army
This weapon is clearly a rocket/missile launcher, but what type is it? Roger (Dodger67) (talk) 12:46, 2 December 2016 (UTC)


 * Starstreak - LML variant, with one of the three positions filled. This article has this picture of the right side of an empty LML for comparison. -- Finlay McWalter··–·Talk 13:07, 2 December 2016 (UTC)


 * Thanks, that is conclusive. Roger (Dodger67) (talk) 13:14, 3 December 2016 (UTC)

What is the reason that not any mammal can be reproductive from another different mammal?
What is the reason that not any animals can be reproductive from another different animal? For example, two mammals like sheep and cow or even a sex of human with dolphin can not results in shared offspring. Just few animals are known to be successful with different mammals, such as: donkeys and horses that make together mule or hinny. so the question is What does make those two different mammals to be successful in reproduction)? is it the number of the chromosomes the key for the issue? and then any mammal which has the same number of chromosomes (2n=46) is matached to be reproductive with human being? 93.126.88.30 (talk) 15:47, 2 December 2016 (UTC)


 * Number of chromosomes is a factor, but not the exclusive one. Some mutant animals have extra or fewer chromosomes, yet can still reproduce with others of their species.  Also, very different animals that happen to have the same number of chromosomes can not reproduce.  To understand this, think about blood type.  People with incompatible blood types can not share blood.  For organ transplants, there are far more such factors to consider when tissue matching.  Well, in our genetics there are even more such factors, making animals with two sets of incompatible genes unable to survive, meaning they may die in utero shortly after conception, if conception even occurs. StuRat (talk)


 * Organ/blood incompatibility is not the limitation - see chimera (biology). The evolution of reproductive isolation is a trickier thing.  See speciation, hybridization.  Actually, I remain very curious whether it is possible to select organisms that are good at hybridization, say, if you cross several species and keep selecting for those that form hybrids most effectively.  There are naturally occurring animals that are somewhat infamous for their ability to hybridize, e.g. mallards, and conceivably they might show surprising ways to compensate for reproductive barriers.  But I don't know any of that, nor is there good reason to think it true! Wnt (talk) 19:41, 2 December 2016 (UTC)


 * Regarding chimeras, that's two sets of genetic codes from the same species, so we would expect that sometimes they would be compatible and sometimes not. Perhaps chimera conceptions are far more common than we think, but due to genetic incompatibility many die before the mother is even aware of a pregnancy, and only the few that are genetically compatible survive. StuRat (talk) 03:57, 4 December 2016 (UTC)
 * Oh, chimerism is much more fun than that! Look it up... Wnt (talk) 04:02, 5 December 2016 (UTC)


 * You may be interested in Humanzee and Mythological hybrid. The answer to your question is that fertilization will not even occur.  (But perhaps if the DNA is directly injected into the egg this restriction could be bypassed) Graeme Bartlett (talk) 11:28, 3 December 2016 (UTC)


 * Actually, the story with humanzee is that the verdict is still out. In biology the only way you know something is to do the experiment, and in the case of hybridization, it can take many attempts before a single hybrid is obtained.  Until someone fesses up to doing the science (with proof, and completed data) nobody knows. Wnt (talk) 12:40, 3 December 2016 (UTC)

Why do animals have hearts ?
...as opposed to each blood vessel squeezing the blood past the next valve, in a process similar to intestinal peristalsis, only faster. I understand that some simple animals, such as worms, do use such a system, which would appear to be more fault tolerant and thus I would expect evolution to favor it. However, it must not scale up well. Why is this ? StuRat (talk) 15:52, 2 December 2016 (UTC)


 * A very round-about way of answering is asking why we have a 4-chamber heart. Consider just the heart and lungs so this doesn't need to take 30 pages of biology... One side takes blood from the lungs, full of oxygen, and pushes it out into the body. The other side takes dirty blood from the body and pushes it into the lungs. That can be done with two hearts. One to pull blood out of the lungs and push it through the body. The other to pull blood from the body and push it into the lungs. Why do we have two of nearly everything and only one heart when our system is designed for two hearts? With one heart, we don't have to keep it in sync. Both sides beat at the same time. It is simpler - and nature seems to like simple things. With that in mind, consider having about 500 miniature valvular hearts throughout the body. There is a lot of redundancy, but there is also a lot of room for error. Throughout evolution, blood circulation was consolidated to a single structure and then that structure split into chambers to perform multiple functions per beat. Please don't read this to imply that "evolution made it that way." As always, evolution is not an engineer. Evolution is just an observation of what happened in the past. 209.149.113.4 (talk) 16:49, 2 December 2016 (UTC)


 * Consider a system where an animal had hundreds - or thousands - of pumps distributed throughout their circulatory system. The distribution of nodes might be more fail resistant (not unlike the internet) but what happens if a few of those pumps fail? What happens if they pump out of rhythm? Sometimes it makes sense to put all your eggs in one basket if you're willing to build an extremely reliable basket. Matt Deres (talk) 17:39, 2 December 2016 (UTC)


 * The heart does most of the work, but not all the work, in the human circulatory system. Please see the Skeletal-muscle_pump. Dr Dima (talk) 18:40, 2 December 2016 (UTC)


 * Of some relevance to this is that some reptiles have a 3-chambered heart - see Reptile. DrChrissy (talk) 20:18, 2 December 2016 (UTC)


 * Humans have a three chamber heart for a significant time during development. Many people don't fully form a wall dividing the large chamber. It leads to multiple health problems. — Preceding unsigned comment added by 71.85.51.150 (talk) 02:26, 3 December 2016 (UTC)
 * Not exactly. See fetal circulation. The fetal heart normally develops four chambers, but there are holes in the septum to allow oxygenated blood from the placenta to mix. These normally close at birth, but sometimes they don't, which can lead to health problems. I think this is what you're referring to. --47.138.163.230 (talk) 04:03, 5 December 2016 (UTC)


 * Note that arthropods have an open circulatory system, where their "blood" (formally hemolymph) is not always contained in vessels, so your proposed system wouldn't work for them. I skimmed a few articles but couldn't find anything about the evolution of the circulatory system and whether it evolved independently in vertebrates and invertebrates. If not, the reason would be pretty simple: the heart came first, and closed blood vessels came later. As others have touched on, in general, evolution works on the principle of "good enough". Animals developed a single heart for whatever reason, and it's good enough, so there isn't much selective pressure to develop an alternative. --47.138.163.230 (talk) 23:24, 3 December 2016 (UTC)


 * Just looking at humans, heart disease is a major cause of death, and while most women so affected are past their reproductive years, that's not true of men. So, that would put selective pressure on humans. StuRat (talk) 04:01, 4 December 2016 (UTC)


 * A bit, but not a lot. Cardiovascular disease generally manifests many years after sexual maturity, so its impact on an animal's reproductive fitness is small. Also, there's an important distinction to make here. Although "heart disease" is often used to mean "cardiovascular disease" (indeed, here on enwp one redirects to the other), the most common type of cardiovascular disease is coronary artery disease. This is not a disease of the heart proper, but rather of the arteries supplying the heart with its blood supply. If you didn't have a heart, you would still be susceptible to atherosclerosis. I also wonder about the feasibility of your proposed system. Arteries already have to be thick to withstand the arterial pressure. If arteries did the actual pumping of blood, they would need even thicker muscle layers. This might cause issues with the amount of space arteries take up, and in getting the blood supply to the muscle layer. --47.138.163.230 (talk) 04:03, 5 December 2016 (UTC)


 * The previous statement from StuRat appears to based on the idea that "heart disease" is limited to the heart. That is not common. If birth defects are thrown out, nearly all heart disease is a localized problem caused by cardiovascular disease. Weak arteries, arterial plaque, etc... If modern humans had hundreds of hearts spread out over the body, there is no obvious way how that would limit cardiovascular disease. Without limiting cardiovascular disease, all of the hearts would be under a greater load and risk heart disease. 209.149.113.4 (talk) 16:46, 5 December 2016 (UTC)


 * Since there would be lots of redundancy, if some segments were clogged up, there would be automatic bypasses. The blocked segments could then be cleared out, and the flow restored.  As for the space taken up by this, the lack of a central heart of large blood vessels (aorta, vena cava, etc.) would free up some space. StuRat (talk) 17:03, 6 December 2016 (UTC)


 * See also here. Count Iblis (talk) 00:13, 4 December 2016 (UTC)

How heartless animals might work

 * There would be more, but smaller, veins and arteries, with redundancy, so that severing one would not cause death.


 * Each valved segment would contract X milliseconds after the previous segment, or after Y milliseconds, if no signal is received. The brain would send out signals modifying X and Y, to increase the blood circulation rate during athletic events, slow it down while sleeping, etc.

So, if this system just wouldn't keep up for animals with a fast metabolic rate, how about slower animals, like sloths ? StuRat (talk) 13:38, 4 December 2016 (UTC)


 * I think we need to be very careful about terminology here. This sub-thread heading uses the word "heartless".  Even a tube-like structure such as discussed above is called a "heart" - see Heart. DrChrissy (talk) 23:56, 4 December 2016 (UTC)


 * If you did that, then such an animal might have thousands of "hearts". I think a different name would be in order. StuRat (talk) 05:06, 5 December 2016 (UTC)


 * "The heart in arthropods is typically a muscular tube that runs the length of the body, under the back and from the base of the head." This is a quote from Heart (my emphasis). DrChrissy (talk) 20:24, 5 December 2016 (UTC)


 * Yes, but note the "a" in the quote. When you have thousands of them working in unison, they are more of a collective heart, rather than thousands of individual hearts.  For comparison, look at a compound eye, where each individual lens segment is not called an eye, but rather the collection of many is. StuRat (talk) 03:37, 6 December 2016 (UTC)

Sea anemone. Count Iblis (talk) 08:20, 5 December 2016 (UTC)

Atomic particle identification
I don't know how to express the following, please try to understand:

There is a particle you find sometimes after an artificial (man made) atom collision that exists in two places at the same time. Does anyone know what the name is? 103.230.104.6 (talk) 18:20, 2 December 2016 (UTC)


 * I believe that applies to all sub-atomic particles, before or after collisions. See wave function and Heisenberg uncertainty principle. StuRat (talk) 18:57, 2 December 2016 (UTC)


 * I'm not thinking of anything specific either, but see two-slit experiment. Wnt (talk) 18:58, 2 December 2016 (UTC)


 * Yes, that might be what they meant. There's no collision involved, but the particle sent towards the slits behaves as if it travels through both slits at the same time.  Here we get into wave-particle duality. StuRat (talk) 19:00, 2 December 2016 (UTC)

Are you guys sure, cause I'm not. All I recall (which could be wrong), a rare particle displays in two places at the same time (sometimes) after bursting an atom, in less than a milli/nano second or so. They are identical/twins. 103.230.104.18 (talk) 08:10, 3 December 2016 (UTC)


 * Some sort of quantum entanglement, such as this experiment? DMacks (talk) 10:48, 3 December 2016 (UTC)


 * And some type of quarks spontaneously change type. Seems less likely to be what you heard though. StuRat (talk) 03:53, 4 December 2016 (UTC)

supermassive black holes
Scientists have found black holes that are several billion solar masses. Is there evidence or scientific speculation of much more massive black holes, perhaps trillions, octillions or even more solar masses?144.35.45.53 (talk) 19:26, 2 December 2016 (UTC)
 * See Supermassive black holes, which states that there is no known mechanism for the generation of so-called ultramassive black holes, and that there is thought to be a limit of the size. Robert McClenon (talk) 21:17, 2 December 2016 (UTC)
 * The actual paper that produced that claim only states that black holes cannot grow beyond this size through the consumption of an accretion disk, while they can still grow further through black hole collisions. The maximum size of a black hole that expands through accretion is proposed to be 50 billion solar masses in ordinary conditions, and 270 billion solar masses in "perfect" conditions. Black holes beyond this size, not having a visible accretion disk, would be hard to detect. Someguy1221 (talk) 22:48, 2 December 2016 (UTC)
 * Ultramassive black holes might be detectable by the effect of their gravitational field on nearby galaxies or by gravitational lensing. Graeme Bartlett (talk) 11:54, 3 December 2016 (UTC)

alcohol hand gel
Please can you tell me what percentage of alcohol this specific product contains, and whether or not it will kill most bacteria and fungi within 30 seconds. The page is vague and does not say. I see these hand gels in hospitals and I want to know if they would be effective. Thanks for your help. — Preceding unsigned comment added by 125.141.200.13 (talk) 19:59, 2 December 2016 (UTC)
 * You might do better by asking the makers.
 * As to its effectiveness, then many products will kill or remove "most" bacteria. However that's nothing like effective enough. Even the much touted TV advert claims of "Kills 99% of all known germs" are nothing like effective enough - 1% of a contamination remaining will still be "contaminated", in practical terms.
 * Alcohol gels are remarkably effective though, compared to handwashing with soap. Their other advantage is that they're effective even with poor technique - unlike soap, which needs conscientious scrubbing to be comparably effective. Andy Dingley (talk) 21:54, 2 December 2016 (UTC)


 * on all of that. Our article covers some of the details, which suggest that the situation is much more complicated than the opinions expressed above. Matt Deres (talk) 17:12, 3 December 2016 (UTC)


 * FYI, I had to reload your link as the first time I clicked it, I was redirected to the suppliers homepage. Anyway, the SDS for product 5665-02-INT00 is here:   It doesn't discuss effectiveness, but it does identify the key ingredients as Sodium Laureth Sulfate >=1 to <5 and Cocamidopropyl Betaine >=1 to <5.  I would describe this as a standard hand soap.  It has no particularly special properties and though all soaps are effective are removing bacteria, this one has no claim to being special in that regard.  Please note that the manufacturer, Purell, also makes products that are intended for healthcare use, including ones certified for use by surgeons and others requiring a highly effective antibacterial soap.  Some of those products come in similar form factors, so if you were expecting this soap to be especially germicidal, perhaps you indicated the wrong product number.  Dragons flight (talk) 22:37, 2 December 2016 (UTC)
 * Agree with Dragons flight. This product doesn't even appear to be marketed as a hand sanitizer, but rather as a hand soap. It likely doesn't contain alcohol as an active ingredient. As a side note, most hand sanitizers, including for hospital use, contain somewhere around 70% ethyl alcohol or isopropyl alcohol. This is the percentage recommended by the CDC for use under biosafety conditions. https://www.cdc.gov/biosafety/publications/bmbl5/bmbl5_appendixb.pdf --OuroborosCobra (talk) 00:23, 4 December 2016 (UTC)
 * According to the bottle I have here, the ingredients are; "Aqua, Sodium Laureth Sulfate, Cocamidopropyl Betaine, Critic Acid, Disodium Cocoamphodiacetate, Glycerin, PEG-80 Sorbitan Laurate, Polyqautermium-39, Benzyl Alcohol, Sodium Benzoate", however it does not give percentages. — Preceding unsigned comment added by 125.141.200.13 (talk) 00:54, 4 December 2016‎ (UTC)
 * The alcohol on their (benzyl alcohol) isn't one commonly used for sanitization of surfaces. It is so far down the ingredient list that I also doubt that as the use. The sodium benzoate, for example, is a preservative. This is hand soap, not hand sanitizer. Remember that the lower something is on an ingredient list, generally the lower its percentage in the product. --OuroborosCobra (talk) 02:02, 4 December 2016 (UTC)
 * Just to check: aqua, sodium laureth sulfate, cocamidopropyl betaine, citric acid, disodium cocoamphodiacetate, glycerin, PEG-80 sorbitan laurate, polyquaternium-39, benzyl alcohol, sodium benzoate.  Note spellings for citric and polyquaternium.  I think we're missing PEG-80 sorbitan laurate entirely, but it exists; see .  I tweaked the disambiguation page for aqua to give the INCI explanation. They're the King of the Goos, I take it. Wnt (talk) 18:30, 6 December 2016 (UTC)