Wikipedia:Reference desk/Archives/Science/2016 June 17

= June 17 =

How reliable are those DNA for discovering your ancestry?
Since a couple of years, I see ads for DNA tests that claim to draw your genealogical tree. They appear to be getting cheaper with time too. How reliable are their results? Can they really know that I'm 5% Inuit, 1% African, 14% North European and so on? — Preceding unsigned comment added by Hofhof (talk • contribs) 01:13, 17 June 2016 (UTC)
 * Genetic Ancestry Tests Mostly Hype, Scientists Say Shock Brigade Harvester Boris (talk) 01:23, 17 June 2016 (UTC)


 * That article is quite a few years old and has its own bias. "One problem with this approach, scientists say, is that because such tests analyze less than 1 percent of a person's genome, they will miss most of a person's relatives. 'If you take a mitochondrial DNA test, you learn something about your mother's mother's mother's lineage,' Bolnick said." Testing 1% will miss most relatives - unproven and possibly irrelevant. mtDNA - not even the kind of test the rest of the article is about, why mention it? Rmhermen (talk) 14:12, 17 June 2016 (UTC)


 * Ultimately, you're 100% African, just like every other human being on the planet. {The poster formerly known as 87.81.230.195} 185.74.232.130 (talk) 13:35, 17 June 2016 (UTC)
 * Nope. 200.165.153.116 (talk) 16:47, 17 June 2016 (UTC)


 * Recent African origin of modern humans &#40;&#40;&#40;The Quixotic Potato&#41;&#41;&#41; (talk) 14:33, 17 June 2016 (UTC)


 * While modern humans certainly interbred with archaic humans outside Africa, those archaic humans (Neanderthals, Denisovans and unknown-as-yet others, possibly even Erectus) had themselves evolved from ancestors who had originated in Africa, which is why I said "ultimately". {The poster formerly known as 87.81.230.195} 5.66.223.127 (talk) 23:31, 18 June 2016 (UTC)


 * And ultimately, they all evolved from fish, which evolved from bacteria, etc., but the tests we are talking about are really only trying to figure out which population of humans a specific person's ancestors were part of a few hundred to a few thousand years ago. Dragons flight (talk) 15:33, 19 June 2016 (UTC)


 * Our article Genealogical DNA test touches on this kind of test only briefly and with few references. Rmhermen (talk) 14:12, 17 June 2016 (UTC)


 * Yep. There is indeed some hype, but this is not snake oil. Human_Y-chromosome_DNA_haplogroups are real, and they can in principle be used to asses they type of heritage OP mentions. I have no idea if any given company offering services today is doing it right though ;) SemanticMantis (talk) 15:16, 17 June 2016 (UTC)


 * Most of the tests being advertised currently in terms of ethnic composition test autosomal DNA rather than just mtDNA or just Y-DNA. - Nunh-huh 15:59, 17 June 2016 (UTC)


 * So far the discussion has been on whether it is feasible with current technology to accurately describe a person's ancestry. We should also consider this from another POV, that is, whether it is in the financial interest of these companies to spend as much as it would take to do so.  That is, who would know if their results are accurate or not ?  If the answer is nobody, then why would they bother to spend the money ? StuRat (talk) 05:16, 19 June 2016 (UTC)


 * If you are so determined to discover your ancestry, or to vet such companies, you could have your DNA tested at two companies. The results also have to be consistent with what you know about your ancestry. If you are half-Japanese half-European and the result is that you're half-African half-Native American, then you know there's something wrong going on.Llaanngg (talk) 14:40, 19 June 2016 (UTC)


 * That would help, assuming they are actually independent companies. Not having your name linked to the results would help, too, as otherwise they might just dig up your name (or address) from the DNA profile done by their sister company, and repeat the same results. StuRat (talk) 15:09, 20 June 2016 (UTC)


 * My wife and I both had ours done by 23andMe back when they were still doing both ancestry and health profiles. As far as the ancestry data goes, we got mitochondrial lineages, Y-chromosome lineage (for myself only, obviously), and lineage of our autosomal DNA, including graphics saying which part of each chromosome they identified with which regions of the globe.  As we both know our family trees for several generations, we could check the results, which appeared entirely reasonable.  My wife is perhaps unusually tricky since within four generations she has ancestors on three different continents.  I don't know that I would trust such results with a really high level of granularity or specificity but in terms of identifying broad patterns I would say they seem to work reasonably well.  Dragons flight (talk) 15:26, 19 June 2016 (UTC)

When is Time Travel paradoxical?
My question on the “grandfather paradox” is more of a speculative rumination. The following note from the WP page here provides the standard account of the time travel paradox: Your actions in that time might then prevent your grandparents from ever having met one another. This would make you not born, and thus not step into the time machine. So, the claim that there could be a time machine is self-contradictory. I noticed that all such accounts involve a human making a conscious decision to challenge the paradox by deliberately changing the past. When an agent does not have this motive, the paradox never occurs. In the billiard ball example given in that WP page, one can simply say that if such a ball on a billiard table went back in time, it could not bump its earlier self into a pocket (effectively the same as killing one’s earlier self), and the paradox never occurs. Thus, we cannot go back in time a week and cut down a tree in our back yard which we have seen growing there yesterday. But we CAN go back in time and cut down trees which no one has ever seen. In the latter case, it can logically be asserted that a causal loop is present in which that cutting down by a time traveller was always part of the history of the world.

My point is that it seems strange that the paradox of time travel only arises when we posit a universe in which there are agents who can travel in time, and who also possess the following properties:

1. They are conscious

2. They are intelligent enough to comprehend the time travel paradox

3. They are wilfully intent on changing the past in order to create this paradox.

This means, of course, that time travel in a billiard ball universe will never trigger a logical paradox, but it also means something even more astonishing. A world full of animals which can go back in time, inadvertently or deliberately (say to escape a predator), will not trigger it either. Nor will human being who are not aware of the potential of a paradox and never deliberately try to create one.

To assert that some unconscious agent - like a billiard ball - might trigger the paradox without any intention of doing so is like saying that a pair of dice might roll a 13. In the inanimate world, if some scenario is defined as impossible, then it just does not happen. As simple as that. We can move by incremental steps from the inanimate world to the organic one, and show that no increase in complexity, or even consciousness, will amount to the possibility of logical paradox, unless the three provisos listed above obtain.

I find it a stirring thought that fundamental principles of the structure of our universe can be determined by whether consciousness exists, and even further, on what such a consciousness wishes to undertake. Imagine that a universe without conscious and wilful agents is very different from a later one in which such beings have evolved, gradually closing the gateways to possibilities that had hitherto yawned open. Is that not a strange concept?

The anthropic principle may come into play. Perhaps the universe we inhabit could never have been structured to allow for time travel; as such a world could never accommodate a conscious entity that challenged the paradox. In other universes, entities there might move back and forwards in time as easily and as often as they do in space, and no paradox ever arises. But then, neither does a conscious agent intent on subverting it. Myles325a (talk) 05:42, 17 June 2016 (UTC)


 * Nonsense &mdash; of course an unconscious actor could trigger the grandfather paradox. Imagine a nuclear bomb that goes back in time and detonates, destroying the factory that created it. A time traveler removing the conditions that allowed it to travel through time (or exist at all) does not require the time traveler to act with intention, be conscious of time travel, or even be alive at all. The rule that unconscious time travelers cannot create paradoxes is one that you just invented right here, right now. Someguy1221 (talk) 11:06, 17 June 2016 (UTC)

OP myles325a back live. When I wrote my q., I went to bed thinking that almost certainly someone will post in to rubbish it coz an inanimate or unconscious agent could easily trigger the paradox. . I thought that I had expended considerable effort to forestall this obvious objection, but no, the usual knuckleheads will spend one second perusing my q. and then another second posting a stupid response. Let me explain the nature of what a paradox requires of us. I am a fan of the International Movie Data Base (IMDB), and there each movie is provided with a section called “goofs” in which contributors can nominate mistakes in the movie. Typically, the main ones are “continuity errors”. For example, someone will post that a man is shown knocking on the front door with a cigarette in one hand. Then when the door is opened, he is shown from another angle, and now he has no cigarette, or his tie has changed colour etc. Suppose we grant that cigarettes instantly disappearing or ties changing colour by themselves are impossible events (tho they are not really, but close to it – Steve Baker (writing below gave me an excellent dissertation some years ago on how virtually NOTHING is completely impossible). If however we grant for argument’s sake that some depicted events ARE impossible, and we grant that we are seeing something that LOOKS impossible, we must accept any solution to the apparent paradox, no matter how unlikely it is, as long as that solution is in itself possible. For example, we may posit that in the instant that the door was opened, the visitor threw away his cigarette. And, if we accept that movies do not need to be in real time but can move from one scene to another omitting some time, we can then posit that the visitor changed his tie in that elided time. If fact, most IMDB errors could be explained in this way if such a need arose, but the only time such unlikely explanations would be required is when they are needed to explain some event which appears to be impossible.

In much the same way, if we accept that a logical paradox arises if an agent moves back in time, and makes some change there which is inconsistent with what he sees in the present (as in the grandfather thought experiment) then we must accept any explanation which is consistent with what we know of reality, and which is not logically impossible. In someguy 1221’s example of an unconscious person changing time can be answered by simply saying that if such change is logically impossible, then it simply cannot and does not occur. It is like the question: “What if someone rolled two dice and got a 13?” It does not happen. Similarly, the problem of the paradoxes is obviated if there is some explanation for the phenomenon which is not logically impossible. My point was that an inescapable paradox only ever arises where a conscious and wilful agent deliberately tries to bring about such a paradox. With inanimate or unconscious agents, the paradox never arises for the same reason that no two dice ever roll 13. Myles325a (talk) 05:59, 20 June 2016 (UTC)


 * Given this definition: PARADOX n. a statement consisting of two parts that seem to mean the opposite of each other. Therefore a paradox can arise only where there is a conscious observer who draws (rightly or wrongly) conclusions. Speculators about Time travel should clarify whether the travel they posit conforms to known Conservation of energy laws (including Mass–energy equivalence) or violates them. In the former hypothesis, the time travel is simply another Action at a distance that can be grouped with theories of gravity and electromagnetism, and is neither inherently "nonsense" nor readily falsifiable. In contrast, the latter hypothesis is peremptorily dismissible citing Reductio ad absurdum. AllBestFaith (talk) 12:52, 17 June 2016 (UTC)

More interesting is the position that, given infinite universes, there should then exist an infinite subset of universes differing from each other only in the apparent current date and time - thus one could go "sideways" to a universe in with its current date in the "past", which is really currently existing the universe you started in, and then a side-step to a current universe from that parallel universe would show the effect of such a change, but without affecting one's own existence (possibly then anomalous, but not contravening any other laws). "Time travel" within a single current universe has more problems, but "apparent time travel" to an alternate universe would seem a lot easier to hand-wave. Collect (talk) 13:28, 17 June 2016 (UTC)

You need free will, but free will doesn't really exist, humans are ultimately just machines. If time travel is possible then whatever has happened in the past already includes all the actions of any future time travelers. If you want to travel back in time in order to "change anything" then whatever you want to do already happened in the past with the known results. If you think you were unaware of some relevant things and want to act differently given what you know now, then it necessary follows that the act of traveling back in time will change your memories to make you act exactly according to script. Count Iblis (talk) 20:30, 17 June 2016 (UTC)


 * Will (free or otherwise) doesn't have to be involved here. We know that chaos theory predicts the so-called "butterfly effect"...so any disturbance to the past of any kind (ultimately, just moving one atom by one femtometer) is sufficient to change large scale phenomena at some future time.  Those changes don't 'die away'.  One beat of a butterfly's wing can cause a hurricane big enough to kill a dozen people - who's children, grandchildren and so forth, will either not exist - or have entirely different DNA.  It would be impossible to make the slightest change to the past without having some kind of cascading change in the present.  You don't have to kill your grandfather to cause a paradox...simply being there is likely to be more than enough to cause noticeable changes over a few decades.
 * We have no scientific reason to believe that time travel would ever be possible - and so asking what would happen if you could is a bit silly.
 * There is also an issue of what happens if you change something in the past - it might cause a paradox...but then it might not. Science fiction never seems to agree on this one (often, as with StarTrek, they aren't even consistent within one fictional universe). So if you go back to the time of the dinosaurs and stomp on a butterfly...
 * You can't return to the present, so what happens there is moot.
 * When you return to the present, it's as though you never stomped the butterfly.
 * When you return to the present, everyone evolved from lizards, everything is different - but you haven't changed.
 * When you return to the present, everyone evolved from lizards - but everything else in the world is more or less the same, we still have cars made by Ford and the (lizard) president is still called "Obama".
 * When you return to the present, everyone evolved from lizards - and so have you.
 * When you return to the present, everyone evolved from lizards - and now there are two of you (one is a bit "lizardy", the other not).
 * When you return to the present, everyone evolved from lizards - but everyone remembers how it used to be before you changed it, so you get the blame for the "lizard-thing".
 * When you return to the present, it's as though you never stomped the butterfly, but you remember that you did.
 * When you return to the present, it's as though you never stomped the butterfly, you remember that you did - but your on-board computer mysteriously didn't capture any information about that.
 * When you return to the present, you don't remember a thing about the trip - but your on-board computer contains information about you stomping the butterfly.
 * At the instant you stomp the butterfly, the future you changes into a lizard-man, so the 'you' in the dinosaur era also changes - so everything stays perfectly consistent. But maybe you create oscillations in the timeline by changing the future in such a way that lizard-you doesn't stomp the butterfly - so things return to how it was if you hadn't stomped the butterfly - so now human-you DOES stomp the butterfly - so now you're lizard-you and...Aaarrgggghhhh!
 * You can't stomp on the butterfly, no matter how hard you try - something always happens to stop you.
 * You stomp the butterfly, cause a temporal anomaly and you instantly cease to exist.
 * You stomp on the butterfly, cause a temporal anomaly and the entire universe ceases to exist.
 * You stomp the butterfly, causing the time machine's anomaly-detector circuit to blow up, trapping you in the past.
 * You change the future, and S-L-O-W-L-Y the effect of that catches up with you (pictures of loved ones fade over hours in Back to the Future).
 * You end up creating a fully consistent alternate timeline/universe.
 * The consequences of stomping the butterfly gradually blend back into normality - so the future is never changed measurably (the opposite of "The butterfly effect"!)
 * The time cops come with a replacement butterfly and sort everything out.
 * The time cops have the forethought to arrest you just BEFORE you stomp the butterfly.
 * Events unfold in such a way that you cancel out the effect of stomping the butterfly - so the present is unchanged.
 * I'm sure there are many more. SteveBaker (talk) 18:31, 19 June 2016 (UTC)

OP myles325a back live. I appreciate Steve Baker's comprehensive input here, but I am not so sure that I agree with all the consequences he educes from the Butterfly Effect. I have started a new thread here where I consider some difficulties with these butterflies. (In passing, I might mention that the lepidopterist who took exception to this account, noting that butterflies were no more likely to initiate such an event than any other insect, and in any case, we should acknowledge all those butterflies whose beating wings averted hurricanes and the like from populated areas. Myles325a (talk) 07:07, 20 June 2016 (UTC) https://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Science#Objections_to_.E2.80.9CThe_Butterfly_Effect.E2.80.9D


 * BTW, the original story where a time traveller actually stamps on a butterfly is A Sound of Thunder by Ray Bradbury (1952). Alansplodge (talk) 21:45, 19 June 2016 (UTC)


 * If I had a time machine I'd put a perfect and definitive answer here. I'd go into the future, copy it, return to the present and paste it in, so I wouldn't even have to bother writing it. -- Q Chris (talk) 07:22, 20 June 2016 (UTC)

All of these situations are encountered on a practical basis in the disease state of precognition. For example: imagine you're driving down Route 81 one fine day and you look over at an emergency crossing of the median and you think gee, my whole life I've never used one of those things. And you look how the wheels of the car ought to just barely straddle the giant mud puddle in the middle of it... and just about then you realize you're remembering when you would be driving over it. So knowing what's going to happen, and your role in those random traffic patterns, you try to convince yourself you're going to go back some other way, you've used the exit fifty times, you actually get over in the right lane and put on your signal... but it's all for nothing. You might as well be Faustus watching a heavenly throne fly away into the air. And then you get in the left lane and you go over the bridge and there you are, stopped dead, three car lengths behind the spot, and so you get to make your left hand turn. In the meanwhile, two vehicles clipped each other, a third plowed into them... you know full well that would never have happened except for your chance effect on the patterns to make the thing you remembered. Sure, Ollie North got stuck in traffic for five hours, but five people had to be helicoptered to the hospital. Anyway, that's how it works. The ability to free will makes way for precognition, I'd say because it is actually based on very short-term precognition in the first place. But don't ask me to give you a reference for any of this. Wnt (talk) 00:36, 22 June 2016 (UTC)

Dermatology: Robert-Unna syndrome, who is "Robert" from 1843 ?
I have made some recent additions to the lede for the article on Cutis verticis gyrata including sources (yes, I know some of them need to be improved as far as details and formatting) but I seem to be stumped in identifying the Dr. Robert mentioned in the sources? Can anyone with access to the various medical references identify this guy, perhaps from the work of Paul Gerson Unna? I'm not suggesting that Robert is WP:notable but I would at least like to provide his full name in the article. Thank you. Koala Tea Of Mercy ( KTOM's Articulations & Invigilations ) 06:38, 17 June 2016 (UTC)

PS: While not the focus of my question if anyone has access to the two sources below, any help verifying and improving the formatting of those citations would not be objected to. :) Thank you again. Koala Tea Of Mercy ( KTOM's Articulations & Invigilations ) 06:53, 17 June 2016 (UTC)
 * Jrnl Mind Med Sci. 2016; 3(1): 80-87. <-- This source allegedly supports that Dr. Albiert called the condition "cutis sulcata".
 * Unna PG. Cutis verticis gyrata. Monatschr Prakt Derm. 1907. 45:227-33. This source allegedly supports that Dr. Unna renamed the condition to "cutis verticis gyrata" (CVG).
 * The fons et origo of contemporary references appears to be:


 * See, for example, this paper. The Diven et al paper is available here if anyone has an appropriate subscription. Tevildo (talk) 16:30, 17 June 2016 (UTC)
 * See, for example, this paper. The Diven et al paper is available here if anyone has an appropriate subscription. Tevildo (talk) 16:30, 17 June 2016 (UTC)


 * Doctor Robert? — Preceding unsigned comment added by Deor (talk • contribs) <--- Is a funny person this  is, ja?  Koala Tea Of Mercy ( KTOM's Articulations &amp; Invigilations )

Would an ecosystem of right handed living organisms be able to form a parallel ecosystem here on Earth?
Efforts are under way to create the mirror-image version of ordinary life. While it seems that such organisms should be immune from attacks by ordinary lifeforms, the biochemistry of one doesn't seem to interfere with the other, the fact that all life on Earth is left handed seems to suggest there may be problems with peaceful coexistence. Life appeared on Earth pretty much as soon as the conditions for life to exist were present. If life actually developed from inorganic compounds here on Earth, then other biochemical implementations of life should also have appeared. One may then argue that other implementations were not successful, but that's hard to do for the mirror image of ordinary life as this should have almost the same biochemical properties. But perhaps left handed organisms would have prevented the development of right handed organisms.

So, if we were to create the mirror image of single celled life forms in the lab, could they form an ecosystem and continue to evolve over hundreds of millions of years, leading to right handed animals, or would this process be stopped by ordinary life well before right handed dinosaurs start to roam the Earth? Count Iblis (talk) 20:33, 17 June 2016 (UTC)


 * Perhaps right handed Earth life simply just never existed. Maybe there'd be nothing against an ecosystem with both. Everything would have to evolve for half the food being useless or being able to tell which is food (maybe by random chance the exact same species wouldn't develop and woe to the D-lion that likes the zebras without the horns). Sagittarian Milky Way (talk) 21:28, 17 June 2016 (UTC)


 * Meh. Who can say? But what are they going to eat? And aren't they still edible to regular animals? I have an informed opinion but I don't think it's worth sharing for something that is both so speculative and poorly constrained.
 * Read Competitive_exclusion_principle, limiting similarity, Food web, Trophic cascade, and you can probably come to your own conclusions. BTW, the Archea have left handed structures, left-handed DNA []  , and also a they have positive rather than negatively supercoiled DNA . See also Z-DNA.
 * So, this is cool research, but having a different chirality for important molecules wouldn't make an organism somehow invisible or exempt from competition and predation from "normal" organisms. SemanticMantis (talk) 21:33, 17 June 2016 (UTC)


 * "One may then argue that other implementations were not successful, but that's hard to do for the mirror image of ordinary life as this should have almost the same biochemical properties" – people have actually suggested that the parity violation of the weak force might give a significant advantage to one enantiomer over the other. See Phys. Rev. Lett. 113, 118103. -- BenRG (talk) 23:08, 17 June 2016 (UTC)

Efforts are not underway to create right-handed life - efforts are underway to create right-handed enzymes, which is about as far from creating life as my paper airplane is from being a passenger jet. To Mantis, nah, they would not be all that edible to ordinary animals. Most of our digestive and transport enzymes would fail to work on them. They would still give some kind of response to smell/taste/antigen receptors (so you're right, they would not be invisible to us or our immune systems), and stomach acid would do a job on them. But complete digestion would be quite impaired (for either humans or other organisms), and I suspect if you tried to eat one of these hypothetical animals most of it would pass through unabsorbed. Anything you did absorb would be kind of useless to you, since you would not be able to make direct use of such an organism's sugars or amino acids. Your liver would probably manage to break these down eventually, but at significant energetic cost, so eating them would probably accomplish nothing. The lack of activity of our digestive enzymes would hamper any effect of our immune systems on right-handed pathogens, but they would not get a totally free ride. Antibodies could still be raised against them (although the production of antibodies would be weak since you couldn't load right-handed peptides into MHC for immune modulation), and reactive oxygen species released by immune cells would still do a number on them. On the same token, a right-handed pathogen would have trouble getting any kind of sustenance from a human body. Someguy1221 (talk) 11:34, 18 June 2016 (UTC)
 * So would that work as a diet food? Eat that, don't be hungry? Ariel. (talk) 17:49, 19 June 2016 (UTC)


 * User:Someguy1221 I don't disbelieve you but I'm also a little confused. I see that e.g. L-Glucose can't be used by us, but I can't see why I should expect *most* of our digestive machinery to depend so strongly on chirality. Any refs to help clarify? Or is this just a trend that you notice if you know a lot of biochem? SemanticMantis (talk) 17:39, 20 June 2016 (UTC)


 * It's something I've noticed from a lot of biochem. Many enzymes with a catalytic triad, for instance, require a "handshake" between enzyme and substrate that is dependent upon chirality. Someguy1221 (talk) 19:41, 20 June 2016 (UTC)


 * This is too speculative to answer properly, but I'd suggest thinking about it at different levels. If you make a right-handed anteater you had better have some right-handed ants on hand!  Together with stuff for them to eat, and so on.  Also, if left- and right-handed ants aren't obviously distinguishable, no anteater is likely to have a happy life.  Still, if you start with autotrophs and make a right-handed grass, I imagine it should do quite well, gradually driving herbivores out of whatever area it takes hold in; at which point sure, you can make a right-handed cow to hang around eating it.  Hmmm, then again, most plants work in concert with fungi in the soil, and I'm not sure what communication mechanisms would be fouled up there - certainly a green plant can be grown in sterile surroundings, but the disadvantage might be enough to wipe out the right-handed colony unless that too is available in right-handed form ... Wnt (talk) 15:58, 22 June 2016 (UTC)
 * Oh, and a relevant factor for food consumption might be essential amino acids. Amino acids are chiral, and so the wrong handed organism certainly will not provide them.
 * Still, this is all just speculation. Biology is the art of the possible - try it and see.  But of course in this case it is not something you can try anytime soon! Wnt (talk) 15:58, 22 June 2016 (UTC)