Wikipedia:Reference desk/Archives/Science/2015 September 6

= September 6 =

Humans stiffen after death, but beef is tender
Humans stiffen after death, why is beef tender? Cows don't stiffen after death? The meat is treated to become tender? If you cut a piece of a human, would it be tender too, contrary to the human as a whole? Or are there simply different process involved here?--Scicurious (talk) 02:46, 6 September 2015 (UTC)


 * Your assumptions are totally off, read rigor mortis and beef aging. μηδείς (talk) 02:51, 6 September 2015 (UTC)


 * What assumptions? --Scicurious (talk) 02:56, 6 September 2015 (UTC)


 * (e/c) Our article on rigor mortis answers your questions. For one thing, body stiffness is only transitory in cadavers (i.e. they loosen up again - see the article for details). 99.235.223.170 (talk) 02:53, 6 September 2015 (UTC)
 * Thanks for this answer. Yes, it answer the question.--Scicurious (talk) 02:56, 6 September 2015 (UTC)


 * I'll assume that actually having read rigor mortis and beef aging you now know which of your assumptions were false. Ping me if you have any questions. μηδείς (talk) 19:48, 6 September 2015 (UTC)


 * There were no assumptions from the original poster, just five questions which seem to have been answered. Bazza (talk) 20:05, 6 September 2015 (UTC)


 * There most certainly were assumptions being made by the OP, and those assumptions were partly false, which is why articles were cited. If he had read that information before asking, he would have realized his premise was false, and thus wouldn't have needed to ask. And now that he has read it, he realizes his assumption was partly false. ←Baseball Bugs What's up, Doc? carrots→ 13:59, 7 September 2015 (UTC)


 * Giving the actual answer (that rigor mortis is only temporary) without criticizing the OP or requiring him to read articles to try to find the answer, would have avoided all the drama. The links are good, but there's no reason to deny to OP info we know and tell him to go find it on his own. StuRat (talk) 14:23, 7 September 2015 (UTC)


 * What's with all the extra stars? Anyway, Bazza claimed the OP made no assumptions. Bazza's statement was factually incorrect. And my comments were not criticisms of the OP, but merely factual statements. Sometimes facts can sound like criticism. Sorry. :) ←Baseball Bugs What's up, Doc? carrots→ 14:40, 7 September 2015 (UTC)


 * It's the "I see your mistaken assumption but I refuse to tell you what it is" attitude that is annoying. (Here the assumption was that rigor mortis is permanent.) StuRat (talk) 16:17, 8 September 2015 (UTC)
 * That's part of it. The other part is that rigor mortis affects only humans. I thought that was all rather obvious from the links Medeis provided. But thanks for being explicit. :) ←Baseball Bugs What's up, Doc? carrots→ 01:27, 9 September 2015 (UTC)

Asterisk->colon.--Phil Holmes (talk) 17:17, 7 September 2015 (UTC)


 * If people want a single star in front as their bullet, they should put a bunch of colons followed by a single asterisk at the start. That never produces more than a single star. StuRat (talk) 16:13, 8 September 2015 (UTC)


 * Reading those articles did not edify me. Rigor mortis says the myosin heads break down... somehow.  Beef aging says that the connective tissue breaks down.  Both are kind of vague how that happens.  Nor is it clear to me that cuts of meat don't have rigor mortis, because, well, they're cut.  The muscle could be all tense and how would I really know?   gives a bit more detail but it still doesn't leave me feeling like an expert.  It's clear that butchery is a bloody form of art! Wnt (talk) 21:29, 8 September 2015 (UTC)


 * Well,, yes, the purpose of beef aging is to allow the rigor mortis of the cattle to end, and the meat to soften from endogenous enzymes and the sort of (non-bacterial) decomposition to occur that will normally occur even in a refrigerated carcass. After all, animals aren't at the risk of crystallizing, but of dissolving, and it takes a constant input of energy (normally called food) to keep that from happening.  So in both humans and cattle (which are kept in a meat locker) will first have the blood pool, and the intact muscle fibers lose their mobility (rigor mortis), and then afterwards cell walls will start failing, muscular integrity will end, and connective tissue will weaken.  Aging meat properly depends on how you manage this process, which in expensive cuts can take two to four weeks. (This blog explains pretty well.) μηδείς (talk) 01:13, 9 September 2015 (UTC)

Double organ transplantation
Is it ever possible to retransplant an organ that's been transplanted into someone else previously? For example, Erma Bombeck died of complications from a kidney transplant operation nineteen days earlier. Would there have been circumstances in which giving the newly transplanted kidney to a third person would have been a realistic possibility? Nyttend (talk) 03:34, 6 September 2015 (UTC)
 * Type the word "retransplantation" into Google. You'll answer your own question.  -- Jayron 32 05:07, 6 September 2015 (UTC)
 * Did it occur to you that there were other possible meanings of the same term? I did that, finding stuff like this that uses "retransplantation" to refer to the same person getting two transplants of the same kind of organ at separate times.  Try being slightly welcoming in the future.  Nyttend (talk) 13:00, 6 September 2015 (UTC)
 * In fact, those seem to be the vast majority of links I'm finding on Google. Someguy1221 (talk) 07:35, 8 September 2015 (UTC)
 * It's pretty new, but totally a thing. Avic ennasis @ 06:40, 24 Elul 5775 / 06:40, 8 September 2015 (UTC)

Std statistics
Why is it that according to statistics from organisations like CDC, oral sex transmits STDs less frequently than vaginal sex? Is this because there are less instances of people having only oral sex or is there an actual scientific explanation for this? 90.194.61.153 (talk) 08:12, 6 September 2015 (UTC)--90.194.61.153 (talk) 08:12, 6 September 2015 (UTC)
 * An excellent question. I don't have an answer, but this implies that, although STD rates for oral sex are less than they are for vaginal sex (anal sex is not mentioned), teens that engaged in both oral and vaginal sex had much higher rates of infection than groups that only did one. Not sure what to even make of that. I was expecting to find a RS that suggested that the amount of thrusting played a part (due to the increased chance of introducing small tears in the skin), or perhaps that quickness of clean up played a part (orally ingested semen is either spit or swallowed fairly quickly as opposed to semen deposited vaginally or anally), but all the sources I found were silent on the matter - they were only interested in describing that you might get and the rates of infection, not why they were different. The ref I gave is based on percentages, so - to answer part of your second question - it's not due to less instances. 99.235.223.170 (talk) 14:55, 6 September 2015 (UTC)
 * Pathogens that cause STDs are generally not well adapted for oral cavity (which is a very aggressive environment). This explains why oral sex transmits STDs less frequently than vaginal sex. Ruslik_ Zero 20:14, 6 September 2015 (UTC)
 * Actually, the answer's pretty obvious and they even made a jingle about it: "You'll wonder where the yellow went when you brush your teeth with Pepsodent." Akld guy (talk) 08:14, 7 September 2015 (UTC)
 * I don't disagree, but I'm having a hard time finding a reference more reliable than ourselves saying so. :) If you find one, it would be a welcome addition to several articles I think. 99.235.223.170 (talk) 21:22, 7 September 2015 (UTC)


 * The mouth produces saliva which contains enzymes and antibodies. The throat is constantly subject to aeration, and the stomach is highly unfriendly to pathogens.  The vagina is meant to be a place comforting to single-celled organisms, not bathed in acid or corrosive gasses, an also a place where most std's are designed to succeed by natural selection.  Hence onprotected genital sex is much more prone to transmit stds than unprotected oral sex, ceteris paribus. μηδείς (talk) 03:40, 9 September 2015 (UTC)

Approximately how many generations of ancestors back to single celled organisms?
Hi, I'm wondering approximately how many generations back is my most recent ancestor that was a onecelled organism. Of course, the generations are of different time periods depending on age of reproductive maturity for ancestor species, and I'm asking about number of generations here. Another way to ask my question is: How many "greats" in great-great-...-great-grandparent are needed to reach my most recent ancestor who was onecelled? Billions? Hundreds of billions? Or just 8 generations? ha ha. Thanks, RPeterson2601:681:4902:31B8:A8ED:CEB9:23:AC58 (talk) 09:10, 6 September 2015 (UTC)

One? http://mxplx.com/meme/607/. Widneymanor (talk) 10:10, 6 September 2015 (UTC)


 * It's difficult to answer this definitively, and estimates are all over the map. THIS is an approachable breakdown that suggests 555 million generations (a suspiciously exact number!) is the correct answer. The problem here is that reproductive rates of the simplest multicellular organisms is TREMENDOUSLY variable - ranging from hours for very active species to years or even decades for some extremophiles that live deep underground where the energy required to reproduce has to be acquired very slowly.  "Somewhere in the range of a few hundred millions to hundreds of billions" is probably the best answer you'll get. SteveBaker (talk) 17:42, 6 September 2015 (UTC)


 * How many generations to the earliest common ancestor? Sagittarian Milky Way (talk) 11:50, 7 September 2015 (UTC)
 * More ;-). --Stephan Schulz (talk) 14:27, 7 September 2015 (UTC)
 * If bacteria can reproduce every 20 minutes, what's the upper bound for single celled algae and whatever else single-celled that's in our family tree? Sagittarian Milky Way (talk) 14:59, 7 September 2015 (UTC)
 * The source I linked to said 1.15 trillion generations - but I wouldn't put any particular faith in that answer. "Somewhere in the range of a billion to a hundred trillion generations" sounds reasonable - but we can't know exactly because single-celled organisms reproduce at rates that can be between tens of minutes per generation and decades per generation - which introduces five or six orders of magnitude of uncertainty into the answer depending on exactly which kinds of bacteria we ultimately evolved from. SteveBaker (talk) 19:38, 7 September 2015 (UTC)
 * It's gets even hairier when you realize that even an individual species can encompass those six orders of magnitude uncertainty. Some bacteria that will happily divide in hours can survive as spores for centuries, or frozen for millennia. Someguy1221 (talk) 07:39, 8 September 2015 (UTC)
 * Remember also that even if we only consider the mitochondria in our cells, as per Symbiogenesis we identify at least two different lineages with probably different number of generations before the earliest ancestor. And that's before we include whatever random other stuff we picked up, some of which surely came from viruses, how do you count the generations for that? Plus somewhat akin to Looie496's point, what's your definition for generation time (or distinct generations) for some of the simpler multicellular organisms any way? Nil Einne (talk) 14:59, 8 September 2015 (UTC)
 * When you consider something like certain types of amoeba that reproduce by dividing themselves into two identical halves - it's not completely clear that a generation has passed because the original amoeba never died. There is an argument for saying that the 'original' amoeba is still alive - so the entire span of the species is just one single generation.  The whole concept of "generations" becomes hard to pin down in those very simplest organisms.  However, the ORIGINAL question here didn't include all of those previous generations of single-celled organisms - and was much closer to having an actual answer (although as Looie496 points out, below, the precise moment when colonies of single-celled organisms would be called "multicellular" is pretty fuzzy too). SteveBaker (talk) 00:59, 9 September 2015 (UTC)
 * Forgot to mention IMO the generation thing, as well random stuff we picked up would apply to the earlier question as well. Even ignoring random stuff we picked up, I don't think the number of generations is always a clear cut question for simple multicellular organisms, while sexual reproduction evolved early on AFAIK it's unlikely that we reproduced exclusively by sexual reproduction in the early days. I was originally thinking mitochondria doesn't, but actually while I'm not up to speed with the current theories my assumption would be in the earlier days of symbiogenesis we sort of had whatever our mitochondria and whatever our other ancestor with distinct cells so a sort of multi cellular, sort of organism. Nil Einne (talk) 11:57, 9 September 2015 (UTC)


 * There isn't going to be a definite answer, because the transition from single-cellular to multi-cellular was surely gradual. It seems likely that the earliest "multi-cellular" organisms were something like slime molds, which are basically single-celled organisms, but in certain situations a mass of cells can clump together and the clump can behave like a single coherent entity for a while. Looie496 (talk) 15:09, 7 September 2015 (UTC)

Cacti evolution in the Old World
What was the reason that Old World plants (except Rhipsalis baccifera) in deserts like Sahara, Arabian Desert or Gobi didn't develop the same response to aridity as American cacti did to become cacti too? This says that "some cactus-like plants" did evolve in the Old World due to convergent evolution, but for some reason they aren't true cacti. Brandmeistertalk  12:41, 6 September 2015 (UTC)
 * It's a little unclear what you're asking for. This says that, although there are no known fossil cacti to help inform us, the cactus family probably developed after Gondwana broke into the Americas and Old World, restricting their distribution. Hence, no cacti in the Old World. If you're asking why Old World plants aren't "true cacti" (a question about taxonomy), the answer is that, even if they looked similar, the group would not be monophyletic. If you're asking about why convergent evolution didn't make them more similar, the straightforward answer is that evolution doesn't follow a script as simply as that. Populations survive or perish due to local pressures in their own way. Sometimes, those produce adaptations that look superficially very similar (sharks, dolphins, ichthyosaurs), but, just as often, it produces very different organisms. 99.235.223.170 (talk) 15:13, 6 September 2015 (UTC)
 * Yes, I agree. "True cacti" are defined as members of the biological family Cactaceae, which is defined by descent from a common ancestor, not by features. Looie496 (talk) 16:40, 6 September 2015 (UTC)


 * Two points, cacti are succulents, and there are many non-cactus succulents. Also, Cactuses are peculiar in that what appear to be their leaves in groups like the prickly pears are actually stems, while the thorns are actually derived from what were leaves.  Other succulents don't necessarily follow this growth habit. μηδείς (talk) 19:46, 6 September 2015 (UTC)


 * Euphorbia_obesa_222.JPG The African plants that have gone through convergent evolution and have many shared traits with cacti are the Euphorbia. As Looie mentioned, they are not cacti because we group organisms by common ancestry, not by shapes and forms. We used to do that Taxonomy_(biology), but it didn't work out so well. Folksonomy might also be of interest. SemanticMantis (talk) 14:43, 7 September 2015 (UTC)