Wikipedia:Reference desk/Archives/Science/2016 January 23

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January 23

Developmental stage of cells and freezing

Why does freezing work when we freeze egg cells, embryos, or sperm, but does not work for higher level of development? By work I mean you can still thaw (defrost?) it and get a functional human out of it? --Scicurious (talk) 01:36, 23 January 2016 (UTC)

Probably someone else will provide more details but our article Cryopreservation and to a lesser extent Cryobiology and Cryonics has some details. Note that your idea freezing just works is largely incorrect. For both Embryo cryopreservation and Oocyte cryopreservation, you have to carry out an effective method of cryopresevation or you're most likely not going to have much success. Notably as our article says, human oocyte cryopreservation is still a relatively new technique. (As embryo cryopreservation is older, some women have frozen embryos which were fertilised by a former partner, which can lead to problems if the partner does not wish the embryos to be used.) Even Semen cryopreservation generally uses some method although the large number of sperm in a normal sample means you have a larger margin for error. Nil Einne (talk) 04:15, 23 January 2016 (UTC)

Yes, I mean "freezing an egg cell works" (somehow works, by proper procedure). I.e. it's possible. This is contrary to "freezing a baby", which never works, no matter what you do. I.e. you won't be able to reactivate it. --Scicurious (talk) 13:51, 23 January 2016 (UTC)

for your final statement. AFAIK, and this is supported by the articles I linked to, there's no intrinsic reason based on our current understanding to think it's impossible although it is likely to be very difficult. The reasons why it's so much more difficult with a whole organism where you have to successfully freeze and revive the vast majority of cells in a complex large (in all dimensions) system are given in the article, although many of the, should be obvious with a bit of understanding of ow cryopreservation techniques work and biology and physics. And you already see similar issues when comparing sperm vs oocytes or embryos. Nil Einne (talk) 14:32, 23 January 2016 (UTC)

BTW, my comments and questions have a definite purpose. They are important because if you have a fundamental misunderstanding of what is and isn't possible and how it is and isn't possible; this may very well be one of the reasons why you're having trouble understanding why whole organism cryopreservation for organisms with large & complex body structures like humans (or even Drosophila [1]) is very difficult. And it's not like it hasn't been achieved for adult organisms with simpler body structures like various nematodes [2]. P.S. I don't intend to suggest complexity and size are the only factors although they are big ones. For a variety of reasons certain things may actually be easier to cryopreserve than you would expect comparing to something else. Also I don't think cryopreservation of vertebrates is an active area of research and definitely not dogs or cats or even rats. But cryopreservation of organs is to some extent [3]. This shouldn't be that surprising, if you can't even really cryopreserve a rat heart yet, cryopreserving a whole rat is very unlikely. Nil Einne (talk) 15:42, 23 January 2016 (UTC)

The problem isn't related (trivially) to stage of development, but to size and complexity. We can readily freeze and thaw many types of mature human cells. What we can't (usually) do is freeze large pieces of animal tissue. That is to say, we can freeze, store, and revive primary cardiomyocytes, but not hearts; we can freeze, store, and revive primary hepatocytes, but not livers; and so forth. TenOfAllTrades(talk) 18:41, 23 January 2016 (UTC)

Why we stop producing lactase as adults?

I have read about being lactase persistent is an advantage for survival. Only 10% of the world population are lactase persistent as adults. The 10% that are lactase persistent are results of a mutation occurred thousands of years ago. We are all born with lactase persistent as babies then lose it as adults. My question is why do we lose it as adults? If that was an advantage, why natural selection turned it off during adulthood? Why most people were not lactose persistent until mutation kicked in? All the answers to this question "why" I found online include something like because we don't need milk as adults anymore. Yes, sure, while we don't need milk as much as we do as babies, but it is still considered to be an advantage. Just because we don't need something doesn't mean that thing doesn't have an advantage. That doesn't answer why the gene is turned off in adulthood. Why natural selection was not at work until much later when some new mutations kicked in? Thank you! (p.s.: I don't care about the mechanisms and any other matters; the answers should focus only on the why aspect). 146.151.96.202 (talk) 06:37, 23 January 2016 (UTC)

Because producing lactase uses energy, which takes energy away from other stuff? That's the best answer I can give you. 2601:646:8E01:9089:90DA:8B23:BEB4:5241 (talk) 07:55, 23 January 2016 (UTC)

As is explained in our article Lactase persistence, it was not an advantage in societies that didn't have dairy farming so it was turned of in adulthood. it was only turned back on in societies that had developed dairy farming. Richerman (talk) 11:23, 23 January 2016 (UTC)

Okay, even if it wasn't an advantage in societies that didn't have dairy farming, but it was not an disadvantage either. Why was there the need to turn the gene off as adults? 146.151.96.202 (talk) 21:04, 23 January 2016 (UTC)

There might not have been a need. Maybe it was just a random mutation for no purpose, and with no down side. But if people weren't dairy farming, there would be no natural selection to weed out these mutations, so they would spread through the population until most/all had them. Note: I said "people", but this would have actually happened long, long ago in the early history of mammal evolution. It wasn't until some populations of an advanced ape started raising dairy herds that the reverse mutation became useful. Iapetus (talk) 12:03, 26 January 2016 (UTC)

Infant mammals have only one oral activity which is suck-swallow-breathe and this represent a drain on maternal resources until they develop the skills of eating and swallowing solids. Mammals have various way of encouraging infant skill development as soon as possible, which is an evolutionary advantage in the wild. Lactose intolerance i.e. cessation of Lactase production that causes the infant animal to experience stomach upset if it persists in breast feeding, contributes to the infant seeking independent nutrition.

Are you saying the gene was turned off in adulthood is the natural selection way of encouraging infant independence of its mother? If lactose persistent population can be independent without the gene turned off, this argument doesn't seem to hold. The gene does not need to be turned off for the babies to seek independence. The mother can teach the babies to be independent. I see no harm in keeping the gene on. Why it was turned off in the first place is puzzling me. 146.151.96.202 (talk) 21:02, 23 January 2016 (UTC)

No. Contribute to means help to cause or bring about (Oxford Advanced Learner's Dictionary). It attacks a Strawman to say this argues the cessation of Lactase production is "the essential natural selection way". Do you also need to be given a justification for each developmental change from infant to adult such as loss of Umbilical cord, loss of primary teeth, and loss of Moro reflex? AllBestFaith (talk) 01:57, 24 January 2016 (UTC)

I thought the usual idea was that, if older children kept nursing, they would compete with their younger siblings, to the disadvantage of the latter.

Of course the mother could prevent that. But would she? The same question applies to the "independence" version, actually. It's not absurd that there might turn out to have been an evolutionary advantage in making the weaning more automatic. --Trovatore (talk) 21:36, 23 January 2016 (UTC)

Trovatore. "The same question applies to the "independence" version." Can you explain more what do you mean by this statement? And why wouldn't the mother prevent that? It makes sense that the mother would make the older siblings seek independence, so that she could feed the younger ones with her milk (since the young ones are unable to eat solid food yet). It's entirely possible to become independent without turning off the gene as happened with cultures that are lactose persistent. Again, I see no clear advantage in turning off this gene.146.151.96.202 (talk) 20:21, 24 January 2016 (UTC)

Some human populations have developed Lactase persistence, in which lactase production continues into adulthood. It may have developed as a response to growing benefits of digesting the milk of farm animals such as cattle. Research reveals lactose intolerance in humans to be more common globally than lactase persistence and the variation has been tied to genetics, but that the largest source of variation has been shown to be based on exposure (e.g., cultures that consume dairy). P.S. Sensible consideration of evolutionary factors should identify probable mechanisms without which answers to "why" are only speculation.

See the article sections about Lactase persistence#Evolutionary advantages and Baby-led weaning in humans. AllBestFaith (talk) 14:00, 23 January 2016 (UTC)

I don't know where there is something about this but I think I also read somewhere there is an advantage in stopping the transmission of diseases in having children be appreciably different from adults in various ways, so there is a drive to accentuate differences. Dmcq (talk) 15:21, 23 January 2016 (UTC)

Video and scientific racism

Video in question. Most scientific racism came from whites during the age of scientific racism, but this particular video has it coming from a black man. I know evolution is not a ladder and lifeforms don't become "better" or "degenerate" as they mutate, they merely adapt to the environment, but I was curious if anyone had any direct refutations of what this man is saying. ScienceApe (talk) 17:00, 23 January 2016 (UTC)

There are plenty of easily found analyses of scientific racism. You appear to be asking this question just to show us that a black man can be a "scientific" racist too. --Llaanngg (talk) 18:15, 23 January 2016 (UTC)

(edit conflict) In the unlikely event that this is a genuine question and not a piece of trolling, there's an explanation of this particular theory and the arguments around it at Melanin theory. ‑ Iridescent 18:55, 23 January 2016 (UTC)

What points do you want us to refute? There's no scientific racism involved in the video, the guy is a racist talking garbage with almost no science involved. He claims that white people are a different species to black people and then a few seconds later says that they are the same species. His claims that white people are more prone to depression and violence isn't supported by any research (obviously there are some studies that would support that claim, while other studies would show that black people are more prone to depression and violence). I'm not sure what the 'SAR' gene is that he mentions, but if white people were that prone to a genetic problem it would be common knowledge, not posted by an idiot on youtube 95.146.213.176 (talk) 00:13, 24 January 2016 (UTC)

As I said above, this is not really a question, but a means to spread the word about this deluded black racist. --Llaanngg (talk) 02:05, 24 January 2016 (UTC)

You really think I was trying to spread the word about this guy? I can assure you I wasn't. I was hoping for a direct refutation of the things he was saying. If I was trying to spread his word, I think twitter or facebook would be a better venue don't you think? ScienceApe (talk) 17:26, 24 January 2016 (UTC)

I know people are having a knee jerk reaction to this video which is understandable. I agree, he is an idiot, I was hoping for a refutation of the points he was saying though. He didn't say white people are a different species, he said they are the same species. As for the points I want you to refute, he mentions "SARA" makes white people more violent. Do white people possess this gene at a higher level as he alleges and what does it do? He also alleges that slc2485 gives them pale skin and alleges that it was developed in central asia. At 1:15 he mentions something but I can't make out what he's saying, but he alleges that it gives them straight hair. He goes on to say that 3%-4% of white DNA is from neanderthals. He alleges that they are able to cope with cold weather from the creatine in their skin. He then says at the "demi level" that 4% stretches out to 70% of their skin. These are some of the allegations he's making. Like I said, I'm not saying he's being rational nor am I defending what he's saying. I just want to know if the assertions he's stating are correct or not. ScienceApe (talk) 17:35, 24 January 2016 (UTC)

While I didn't catch the part where he called them a seperate species (he did say something about some people feel they are "something different" and it's cool and people should feel like that), I largely stopped listening when he mentioned demi level. Since "demi level" is not even close to a scientific concept, it's not surprising if the rest of his talk is similarly unscientific. Nil Einne (talk) 00:48, 25 January 2016 (UTC)

I don't even know what demi level means. ScienceApe (talk) 02:22, 25 January 2016 (UTC)

Um isn't that precisely the point? We don't know because it isn't a scientific concept and this is a science desk. If random people are talking random crap in videos where one of their basic points refers to non scientific concepts, then there's little point analysing their videos to find if any of it has any scientific merit in any of what they say. If you don't have sufficient knowledge to dismiss demi level offhand, a simple search will show it's not a scientific term. It's possible that it's simply an incorrect name for a common concept (which considering the person talking clearly speaks good English even using their personal cultural variant is a warning sign in itself); but if there's uncertainty over whether demi level is actually referring to any scientific concept but by the wrong name, it makes sense to ask about that rather than getting in to nitty gritty over whether claimed gene frequencies are correct (let alone whether these genes have any well established link to violence). 09:00, 25 January 2016 (UTC)Nil Einne (talk)

I don't necessarily think we should throw the baby out with the bathwater so to speak. He mentioned other things which may very well be scientific. "SARA" and slc2485 for example. But I agree that "demi level" could in fact be the incorrect term for a real scientific concept. So if that's the case, what is that concept? ScienceApe (talk) 16:56, 25 January 2016 (UTC)

I think you've missed my point. I never said that demi level may be a real scientific concept. I only said if you were initially unsure if demi level was really just a poor name for a scientific concept, you should have asked. You should have already established that demi level is not the real name for a scientific concept by yourself (as that is trivial to establish, there's basically no one else talking about it), so your main question should be "is he just using an uncommon name or is he talking nonsense"? But I already said in my first reply that it was not scientific concept and he is talking nonsense. And as I also said, when people are talking science but get the basics of what they are talking about fundamentally wrong, it does make sense to throw the baby out with the bathwater. Or just to repeat what I said in my first reply Since "demi level" is not even close to a scientific concept, it's not surprising if the rest of his talk is similarly unscientific. Nil Einne (talk) 13:44, 26 January 2016 (UTC)

Your comment is confusing, it seems to be more along the lines of lecturing me on how I'm supposed to be asking questions rather than actually addressing any of the questions I had. I do think you're throwing the baby out with the bathwater, but I don't agree with your rationale for doing so. Just because "demi level" is unscientific doesn't necessarily mean the other things he's saying which weren't in that line of reasoning are false. They may happen to be false, but they aren't false just because he uttered "demi level". ScienceApe (talk) 06:05, 27 January 2016 (UTC)

'Demi level' means 'half level' which makes absolutely no sense in his context (so you can ignore that nonsensical claim). 'sarA' appears to be a gene related to viruses [4] [5]. White people aren't more prone to 'violence inducing afflictions' from viruses, so that's another argument you can strike out. The SLC gene family is involved in melanin production, so naturally all races have different SLC genetics [6]. How could you expect an albino to have the same SLC genes as a black? 'slc2485' (according to a quick google search) is specifically a gene involved in the production of melanin, in combination with other genes, but there's no evidence I can see showing that it might cause violence. I'm not sure why you still insist that something about that video might be scientific, it's blatantly a racist video, and I hope I've responded to all your queries about anything that might have been scientific Mike Dhu (talk) 20:39, 25 January 2016 (UTC)

After a bit more research I think what sounded like 'slc2485' must be SLC24A5, so you could follow that up if you want to. There's some info about its role in skin colour but there's no mention of violence related to the gene. Mike Dhu (talk) 21:58, 26 January 2016 (UTC)

Why does powdercoated metal, like the inside walls of a microwave, not spark?

75.75.42.89 (talk) 23:40, 23 January 2016 (UTC)

Small amounts of metal won't spark. ScienceApe (talk) 23:44, 23 January 2016 (UTC)

Small amounts of metal certainly will spark - have you never put a cup or plate with a gold leaf rim in a microwave? Whether a piece of metal arcs or not depends on it's shape - thin edges or points tend to build up a charge and arc (spark). The side walls are flat with no edges so the microwaves are reflected back and don't build up a charge. Other metal components, such as the metal rack, are designed without points or sharp edges for the same reason. Richerman (talk) 00:54, 24 January 2016 (UTC)

(ec) A metal object in the cavity of a microwave oven can produce sparks if it concentrates the electric field sufficiently to cause breakdown of the air. Whether this is the case depends on the size, shape, position and orientation of the object. A metal object with sharp edges is likely to concentrate the field at the edges, particularly if the size of the object is such that the electric currents on it resonate at the frequency of the applied field (~2.45 GHz). The walls of the cavity do not give rise to sparks because they lack extremities with convex edges, rather than because they coated. --catslash (talk) 01:18, 24 January 2016 (UTC)

Additionally, the fact that the cavity of a microwave oven is made of metal is essential to its operation. The walls of the oven form a Faraday cage, trapping the microwaves inside the oven. If your microwave has a window, you might have noticed the metal grating over it. This is also part of the Faraday cage. The openings in the grate are smaller than the wavelength of microwaves, so microwaves cannot pass through them. Visible light has a much shorter wavelength, so it passes through just fine. --71.119.131.184 (talk) 01:55, 24 January 2016 (UTC)

I think ScienceApe meant small in size. Each granule of the powdercoat metal is insulated from the next granule, so there is no large voltage induced. The gold leaf rim will not spark if it is cut into small sections. Dbfirs 09:15, 24 January 2016 (UTC)

Small amounts are fine. ScienceApe (talk) 16:56, 24 January 2016 (UTC)

Thanks. So you're all saying a smooth steel ball bearing with no small bumps or surface defects could be microwaved without sparking? 75.75.42.89 (talk) 22:06, 24 January 2016 (UTC)

It's not that simple - to quote from here "metal in the oven has to have a certain shape, size, alloy, distance from other pieces etc. or it will really do unpleasant things like arc and get dangerously hot. The rules are complex and as the average microwave oven owner doesn't have a post-graduate degree in physics with at least a minor in high-energy radio it's just easier to say "no metal." Richerman (talk) 18:24, 25 January 2016 (UTC)

Well one of the microwave ovens I had had a nice folder showing that when idle, you should put in it a glass full of water with a 100% metal teaspoon in it. The water would absorb energy if it started by chance and the teaspoon would avoid hyper-heating, allowing it to boil. There are YouTube videos with microwave ovens with forks and spoons put inside them. Tgeorgescu (talk) 00:41, 26 January 2016 (UTC)

Seems to me like it would be a much better idea to just unplug the oven, if you're worried about it being turned on while empty... --71.119.131.184 (talk) 00:28, 27 January 2016 (UTC)

I'm aware of Superheating, and think you may be getting confused with that, it's unlikely a microwave manufacturer would advise you to put a glass of water with a metal spoon in the oven 'in case' you turn the oven on. I've never started my microwave by accident for more a than few seconds, let alone with with a glass of water in in it, as I'd personally use my kettle for heating water. Are you possibly thinking of something such as this popular science question? Mike Dhu (talk) 04:14, 27 January 2016 (UTC)

See e.g. https://www.youtube.com/watch?v=b1MFWbX3Bfc Tgeorgescu (talk) 20:35, 27 January 2016 (UTC)