Wikipedia:Reference desk/Archives/Science/2022 June 30

= June 30 =

Origin of blue eyes
Hans Eiberg has claimed that blue eyes occurred between 6,000 and 10,000 years ago. "Before then, there were no blue eyes." However, for instance, here it says: Homo sapiens arrived in Europe from Near East some 42 000 years ago. Like in their African origin, these humans had dark skin but due to variations of their OCA2 gene (causing iris depigmentation) many of them had blue eyes (cf. the diagram below). Now which is correct? Hildeoc (talk) 00:44, 30 June 2022 (UTC)
 * It is difficult to determine when a particular mutation first appeared in history. So, I would take the claim that it happened 6,000-10,000 years ago with grain of salt. I think that the later work is correct. Ruslik_ Zero 04:45, 30 June 2022 (UTC)
 * Given that this Wiley Book you referenced was a peer-reviewed and edited and published book in 2020, very recently, and this article on livescience.com you referenced was based on a paper published in 2008, a loooong time ago in biological terms, I would state definitively that the Wiley book is more reliable with no further review required. As for determining when mutations occurred in history, it's not a simple question, but there are portions of the genome that evolve more slowly than others and can thus be used to follow populations over places and time (see Mitochondrial_DNA) and that is an important technique in population genetics - determining parts of the genome that evolve slowly, and using those to determine an organism's genetic past. -- Charlesreid1 (talk) 06:27, 30 June 2022 (UTC)
 * Agreed. I'll also add that blanket statements like "Before then, there were no blue eyes." should be treated with suspicion. Our eye color article notes that "Blue eyes are common in northern and eastern Europe, particularly around the Baltic Sea. Blue eyes are also found in southern Europe, Central Asia, South Asia, North Africa and West Asia." and having a single source for blue eyes that recently would mean that all those disparate groups came had a common origin, or at least intersection. Matt Deres (talk) 15:49, 30 June 2022 (UTC)
 * All those people did interbreed, for thousands of years. Shocker. Abductive  (reasoning) 18:30, 30 June 2022 (UTC)
 * Oh indeed. But my point was more that it means that either there were mass migrations of blue-eyed people or multiple mutations causing blue eyes to come into existence or that they all shared a common ancestor 6-10 kya. Those aren't impossible, but you'd want something independently corroborating them before declaring anything. Matt Deres (talk) 20:03, 30 June 2022 (UTC)
 * I would say that all those things are true. Abductive  (reasoning) 10:17, 1 July 2022 (UTC)
 * Is there any speculation that Neanderthals had blue eyes? --←Baseball Bugs What's up, Doc? carrots→ 13:44, 1 July 2022 (UTC)
 * Yes, and red hair. Abductive  (reasoning) 14:29, 1 July 2022 (UTC)
 * But not (I have read) due to the same mutation that results in red hair in the Scots, or the different one that does so amongst Jews – or, for that matter, the one that did so in Mammoths (some of which were also blonde, apparently).
 * We have to remember that most obvious phenotypical characteristic`s, such as hair, eye and skin colour, result from complex interactions of numerous alleles, and there isn't just one "gene (allele) for blue eyes" despite the simplified example most of us were taught in secondary (high) school biology class (see Lie-to-children). {The poster formerly known as 87.81.230.195} 90.195.174.88 (talk) 17:00, 1 July 2022 (UTC)
 * @Abductive: But is there actual evidence that Neanderthal genes for blue eyes were successfully passed on to Homo sapiens?
 * And regarding the source referenced by me above, claiming that many of the Homo sapiens arriving in Europe from the Near East had blue eyes, why – in terms of the logic of evolutionary adaptation – would their iris color have depigmented that long before their skin color? Hildeoc (talk) 17:44, 2 July 2022 (UTC)
 * I was giving the mathematician's answer that yes, there was speculation. Wikipedia's articles Neanderthal genetics and Interbreeding between archaic and modern humans says they did not give us anything fun. The speculation about eye colors is that the change to lighter colors preceded the skin color changes due to sexual selection. Abductive  (reasoning) 18:37, 2 July 2022 (UTC)

Any electrical engineers here?
Ok I am 1 to never thought of to ask this question here. But today at work, I was to train someone in my lab. Later I noticed, when he was on the laptop, it was unplugged. And I talked to him about it. He said he did it on purpose. And told me to not plug it back in, because it hurts the battery when the laptop is fully charged. So I said, "so let it discharge until it's, 5%?" And he said "No, 20%." (Then charge it to 100% and unplug it back to 20%.). And so, I'm at a lost of words here. To not make this a parenting question, and more of a science question, who's in the wrong here? Because, I feel the burden of proof is on him, that this is common sense, but now I realize I only how to think only the way I think and not others, maybe there are others who feel this way? If I am in the right, any electrical engineers can provide a relatively good explanation for this? Note that this is not a question about recharging. 67.165.185.178 (talk) 22:52, 30 June 2022 (UTC).
 * He's mostly right although not about the 100% bit, it would likely be better to cut off charging at 80% or something if you don't need that extra life and aren't going to let it get too low because you didn't charge it enough. Most types of lithium ion batteries in common use, especially those generally used in smart devices have increased capacity loss when charged to or kept at 100% or a high level of state of charge (whatever the manufacturer defines that). This is mentioned in our article under Lithium-ion battery. The general recommendation if you're just storing a lithium-ion battery is to keep it at something like 50% (although it varies depending on how long you plan to store it and the level of discharge expected since you don't want to let it get too low either). The same if discharged to whatever the manufacturer defines as 0%. Although this isn't so clearly mentioned in our article, it mentions depth of discharge but doesn't really explain how this affects cycle life, however depth of discharge does mention this. Most guides which talk about how to take care of lithium ion batteries will also mention this see e.g. [//ehs.mit.edu/wp-content/uploads/2019/09/Lithium_Battery_Safety_Guidance.pdf] [//www.techrepublic.com/article/five-tips-for-extending-lithium-ion-battery-life/] (although doesn't clearly mention the disadvantage of charging to 100% SoC) batteryuniversity.com/article/bu-808-how-to-prolong-lithium-based-batteries. Some devices let you limit the maximum charging voltage or "state of charge" and/or allow you to adjust the discharge cut off point for this reason. Note that lithium ion cells can sustain dangerous damage making the prone to combusting when recharged if they are over discharged so as a safety measure manufacturers do their best to ensure they never get to such a level and may not allow them to be recharged if they do. And likewise overcharging is dangerous. Note also while some electrical engineers will be able to explain in depth why this is the case, I would not assume all, or even most would. Electrical engineering is a wide field, and even with the rapid rise of battery powered devices, I'm sure there are many who only have minimal dealings with batteries and so may only have minimal understanding of their characteristics, further well many lithium-ion batteries are affected, not all batteries are especially when it comes to how maximum charging voltage affects capacity loss. They may be better able to understand some of the papers dealing with it, but OTOH, I'm guessing a lot of people who are not electrical engineers probably have a better existing understanding than many of these electrical engineers who don't know do or maybe even want to. Nil Einne (talk) 23:51, 30 June 2022 (UTC)


 * Official guidance from one major manufacturer of battery-powered portable computers:
 * About Batteries
 * About battery cycles
 * Maximizing Battery Life and Lifespan
 * Guide: Charge the MacBook Pro battery
 * About Optimized Battery Charging on your iPhone
 * One takeaway is that many modern devices are able to self-control and self-regulate their battery charging behavior cycles. The engineers and designers who make the product put effort into maximizing both the battery "life" and "lifespan".
 * Whether the "optimal" battery discharge levels for each cycle are 20%-to-80%, or 5%-to-100%, or any other cycle values, depends entirely on the product. It's unlikely that an end-user can meaningfully guess which values are "best" without reference to the specific product documentation - in fact, the end-user probably doesn't meaningfully have any visibility into what these numbers even measure.  (These numbers express a "percentage" of which parameter, exactly?  Volts?  Amps?  Volt-Amps?  Volt-Amp-Hours?  Amp-hours?  Just plain old hours?  One really cannot know without an engineering specification, and consumer devices don't usually publish one!)  Modern batteries are a bit more complex than a AA-cell: the batteries inside many consumer computers have ...their own separate computer inside the battery (!), complete with custom circuitry, software, and complicated behavior.  Golly, it's 2022: most computer power cables have their own computer inside the power cable, complete with custom circuitry, software, and complicated behavior.  (Here's an official presentation on the USB Power Delivery specification - there's more than copper wire in that cable, and it takes a hundred slides to introduce the subject!)  Seriously, I read a lot about of the history of computing, and the inventors of VLSI and electronics miniaturization — for all their prescience and forward-thinking — really did not ever talk about this inevitable reality consequent to their efforts).
 * So - refer to your exact product's specification or instructions to get the best performance. The real engineering answer is that we should discourage guessing about the inner workings of a hyper-complex system, and point the user to reference their product documentation, and we shouldn't promulgate hearsay or rumors that are based on "approximate" understanding of the engineering principles of complicated battery design.
 * Nimur (talk) 04:44, 1 July 2022 (UTC)


 * I never really looked at battery life or lifespan optimisation of my laptop. I just let it charge to somewhere between 95–100% (or whatever the battery calls 100%) and when I use it, not so often, I don't let it drop below 15%. The battery is now 11 years old and performance drop isn't really noticable (no more than 15%). It looks like not worrying was the right strategy. PiusImpavidus (talk) 09:09, 1 July 2022 (UTC)
 * In terms of rumors, I have heard that the go up to 100%, down to whatever% idea only applies to the first few times with a brand new battery, just to 'educate' the software about the idiosyncracies of that particular battery. Abductive  (reasoning) 10:21, 1 July 2022 (UTC)
 * And furthermore, that the 'education' was only to make the displayed % charge remaining more closely match the true % charge remaining, and it makes no difference whatsoever to discharge rate or battery lifespan. Abductive  (reasoning) 10:37, 1 July 2022 (UTC)


 * The earliest generation of rechargeable batteries for digital computers and electronic equipment (Ni-Cd batteries?) suffered from developing a memory that eventually reduced their effective life. Various strategies evolved for extending the lives of these batteries. I think the strategy described in the original question is a legacy of that era of Ni-Cd batteries. Newer types of batteries do not suffer from a memory and those early strategies are no longer of much value. Dolphin ( t ) 10:50, 1 July 2022 (UTC)


 * For lithium-ion batteries in mobile devices, the purpose of discharging fully and then charging fully is to calibrate the 'full' and 'empty' battery points so that the device's onboard software is able to display a meaningful battery level. (Anecdotally, I ran into a particularly acute example of this when I purchased a USB 'power bank' a few years ago. The first time I used it, I charged it fully and then used it to charge some of my devices on an airline flight. Its seven-segment display fell from 100 to 0% within half an hour, and then it kept charging my devices for another three or four hours with its display pegged at 0% the entire time. After fully discharging it once and recharging it, the charge-level display began to work normally.)
 * Discharging to full depletion is not recommended for lithium-ion batteries (except infrequently for calibration purposes) and does shorten their lifespan. https://news.umich.edu/tips-for-extending-the-lifetime-of-lithium-ion-batteries/
 * Lithium-ion batteries are also stressed somewhat by being charged fully. (This is, incidentally, different from some other battery chemistries. Lead-acid batteries, for instance, are happiest when floated at full charge.) Fully charging isn't nearly as damaging as fully discharging, however. The maximum lifespan of a li-ion battery is obtained by bouncing between a medium-high and medium-low level of charge, never fully charging or discharging the battery. The Asus laptop I'm typing on right now has a battery health tool that lets me cap the maximum charge level of the onboard battery at 80% or even 60% if I want to prolong my battery's life (at the expense of unplugged working time). https://www.asus.com/us/support/FAQ/1032726/
 * If you can plug in, you should--if you're using the wall outlet for power, you're not using the battery at all. TenOfAllTrades(talk) 14:43, 3 July 2022 (UTC)