Wikipedia:Reference desk/Archives/Science/2015 October 14

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

October 14

Atomic composition of moon rocks

anyone? 64.170.21.194 (talk) 03:48, 14 October 2015 (UTC)

Moon rock details the common types of moon rocks and the atoms that compose them. Someguy1221 (talk) 03:51, 14 October 2015 (UTC)

If evolution is real, how come people with mental illness and birth defects exist?

If evolution is real, how come people with mental illness and birth defects exist? Surely millions of years of survival of the fittest should have weeded them out. — Preceding unsigned comment added by 91.225.109.63 (talk) 11:47, 14 October 2015 (UTC)

How likely are kids with birth defects to grow up and have kids of their own? You have to admit, far less likely than those without birth defects. That doesn't stop other people from having kids with birth defects. That's what survival of the fittest means. Now, imagine if a kid was born with a sort of beneficial birth defect. Like, technically it's the same as a birth defect, but it helps them survive better in whatever environment they live in. For example, an inability to taste stuff that's highly nutritious but nasty tasting. They'd be more likely to eat their veggies and have their own healthy kids. If a bunch of these beneficial birth defects start to stack up in family line, you might end up with a brand new species. That's evolution. Ian.thomson (talk) 12:02, 14 October 2015 (UTC)

"Survival of the fittest" doesn't exist in humans. Every human that can make it to adulthood has the possibility (and likelihood) to reproduce. In fact, there is a well-documented correlation that if you consider wealth and education as factors for being fit, the least fit have the most children. 199.15.144.250 (talk) 12:06, 14 October 2015 (UTC)

Survival of the fittest certainly DOES exist in humans. What it doesn't mean, however, is that each individual human is prohibited from biology from ever having, or passing on, any disadvantageous gene. It is a statistical concept, dealing in trends over long periods of time with large populations of organisms, and not with the survivability of individual organisms (see my explanation below). Humans do not exist outside of natural processes, humans are influenced by those same processes, and continue to be. Also, please don't answer questions with merely your own opinions and understandings. Please provide references which explain, back up, or provide additional information. This is the reference desk, not the "tell everyone what I think" desk. --Jayron32 12:13, 14 October 2015 (UTC)

Survival of the fittest is based on passing on genetic information. It is rare for a human to reach adulthood and NOT be able to pass on genetic information. Genetics do not improve a human's capability to get food or shelter. Genetics do not improve a human's capability to avoid conflict and, related, death. Money and education are the two driving factors that influence passing of genetic information. Neither money nor education is based on genetics. If, as many do, you want to bastardize "survival of the fittest" and claim it is not based on genetic information, then congratulations! You can win any argument by haphazardly changing the definition of things to fit your needs! 199.15.144.250 (talk) 15:29, 14 October 2015 (UTC)

Does genetics not give the humans those traits which allow them to do all of the things you're talking about? Does DNA not directly influence the formation of the human brain and give them the ability to do all of the things you're talking about? Are YOU seriously claiming that humans are no longer passing on genes to their offspring? Because when you say "survival of the fittest" doesn't apply to humans, it sounds like you're claiming that genetics didn't play a role in making humans what they are... --Jayron32 20:14, 14 October 2015 (UTC)

Also, on "Money and education are the two driving factors that influence passing of genetic information". Actually wait, don't bother, because the data says it is actually not true at all. To wit "The higher the degree of education and GDP per capita of a human population, subpopulation or social stratum, the fewer children are born in any industrialized country." To wit: The more money and education a population of humans has, the lower their fertility rate and the lower their population growth rate. Rich, well educated population groups have less children which live to adulthood to have children of their own; it's a measurable demonstrable fact. So, not only are you speaking out of your ass when you claim "Money and education are the two driving factors in the passing on of genetic information" by not backing it up with any references whatsoever, the actual references you would find to find the relationship between money/education and the passing on of genetic information is that rich/educated people pass on less genetic information, because they have less children who live to adulthood to pass on their genes. Doesn't it suck when data proves you wrong? --Jayron32 20:20, 14 October 2015 (UTC)

The term "driving factor" has to do with correlation. I already stated that wealth and high education are NEGATIVELY correlated with birth rates and I stated that it is well documented (as you quickly discovered). I have no reason to believe that there is any gene that increases wealth or education. If you take the top 10% of the wealthy people in the world, I seriously doubt you'd find a genetic sequence that identifies them. Similarly, if you take the 10% of the least wealthy people in the world, I seriously doubt you can find a genetic sequence that identifies them. The same with education. Anyone CAN get a college degree. Many people do not. Why? They are expensive and they take a lot of time. It isn't genetic. It is by choice. (Disclaimer: I am a college professor, so my opinion on this matter is based on seeing students graduate every year, drop out every year, and get kicked out every year, regardless of genetics). Further, I have not claimed that humans are not evolving, slowly mutating. I only claimed that "survival of the fittest" does not apply to the current state of human evolution when you use genes to define who is fit and who is not. Genetic information is not correlated to human birth rates for humans that reach adulthood. It is for those who cannot reach adulthood (obviously). In other words, having a gene that makes a person tend to be physically unfit does not reduce that person's chance of reproduction. That person's chance of reproduction is primarily related to the person's wealth and education - which is not genetic. 199.15.144.250 (talk) 14:33, 15 October 2015 (UTC)

Evolution is not determinitive on the individual organism level. Evolution operates over long periods of time, and operates on populations of organisms. Evolution does not create exact, immutable copies of perfect individuals. All evolution (and natural selection, and all associated ideas) says is that traits which tend to increase a population's chance of survival tend to get passed down more often to succeeding generations, while traits which tend to decrease the chance of survival tend to get passed down less often. It doesn't say "no bad thing ever get's passed to future generations ever". Insofar as a trait does not absolutely prevent an organism from reproducing, the trait will be preserved. Since mental illness does not stop people with it from having sexual relations and producing offspring, there is a non-zero chance that the genes which make that illness more likely will get passed to future generations. And thus, it perpetuates. If you would like to learn more about how evolution works, Wikipedia has many articles on the topic, including one titled evolution that is fairly comprehensive. It contains blue links to further concepts which may help you understand more about it if you're confused. There are, of course, several perspectives on evolution (not denying its existence, we're all pretty darned sure it's happening), but some different ways to look at the mechanisms and processes by which it occurs. One of the trendier, more popular (but not uncontroversial) perspectives is the Gene-centered view of evolution, famously expanded on by Richard Dawkins in his book The Selfish Gene. Dawkins didn't invent the theory, but his work is popular because of it's accessibility. Other popular and accessible theories of evolution include the theory of Punctuated equilibrium (which in many ways is in opposition to Dawkins' theory), the most accessible works dealing with it are associated with Stephen Jay Gould, notably his works Ontogeny and Phylogeny and The Structure of Evolutionary Theory. Those works can get a bit technical at times, Gould did write also for a general audience on a lot of topics, he has some essay collections which may be a bit easier to read, including Ever Since Darwin. A book which may help clear a bit up for you is Gould's The Mismeasure of Man, which does a lot to combat the misconceptions you seem to have with biological determinism, based on the questions you seem to have above. --Jayron32 12:13, 14 October 2015 (UTC)

The answers to the two examples are different. Mental illness exists, in large part, because we live in a society that is very different from even a hundred years ago, let alone ten thousand or a million. We simply have not had time to adapt to this society - and, I should note, there is no guarantee that that adaptation would favor the sane. Sociopathy seems to me to be quite an adaptive trait, no? But in the case of birth defects, many of these are driven by fresh mutation. Mutation leads to genetic disease, and yet, without mutation there could be very little evolution. How organisms evolve to have a certain mutation rate and lifespan (because you can't have a lifespan that would permit the build-up of too many mutations between generations) strikes me as an interesting and surprisingly little explored area of research. Wnt (talk) 13:08, 14 October 2015 (UTC)

Nitpick: "Mutation leads to genetic disease" is not really accurate. Some mutations can be detrimental. Others are beneficial (if you can digest non-fermented dairy products in adulthood, which the majority of humans can't, you have one or more mutations to thank). And some are potentially both, like sickle cell trait. Also one tired old creationist argument is the assertion that all mutations are deleterious, so it's worth paying extra attention to wording here. --71.119.131.184 (talk) 13:19, 14 October 2015 (UTC)

I didn't say every mutation was deleterious. But so long as the DNA sequence can be changed, it can be changed in harmful ways, and will be changed in harmful ways some proportion of the time. At best, when the effect of mutation is small, it is about 50% beneficial, because it is effectively a small tweak to the setting on some dial, you might say, that wasn't set with a great deal of accuracy to start with. But if the mutation has a strong effect, that effect is more likely to be harmful. (see hopeful monster) Wnt (talk) 14:46, 14 October 2015 (UTC)

A pretty good response to this question is given here, IMO: If evolution is true, why don't we seem to be currently evolving?.

Technology introduces new factors—e.g. being able to survive and reproduce despite having terrible eyesight—but these factors do not put the breaks on evolution. Human manipulation might allow many individuals to reproduce who wouldn't be able to without modern technological intervention. But we can't control every aspect of nature. For every thing we control, nature has a response.

JoeSperrazza (talk) 13:09, 14 October 2015 (UTC)

Note that the fitness in question is reproductive fitness, not some conformance to an ideal blue-eyed, fair-haired ideal with an IQ of 180, a six-pack, 20/20 vision and perfect teeth. Reproductive fitness always manifests itself in relation to an environment - and if we change the environment in a way that a previously valuable trait becomes detrimental (say the ability to store a lot of calories in the form of body fat), while a previously detrimental trait becomes relatively harmless (say short-sightedness, or type 1 diabetes), then the very same individual will have different reproductive success and hence different fitness. --Stephan Schulz (talk) 13:54, 14 October 2015 (UTC)

Also noted, is that the environment itself is not unchanging; it is changed by the very populations of organisms that are changing in response to the environment. That is, once a population's genetics has changed to meet an environmental factor; that very environment is also changing (since the population is a part of its own environment) so the system is not "progressing" towards some "perfect end point". It is simply changing; not towards anything, but towards "fitness", but what "fitness" is itself constantly changes. --Jayron32 14:14, 14 October 2015 (UTC)

Note that, even with a genetic defect that makes it impossible for the individual to pass down their genes, that defect will never be completely eliminated from the population, in that it will occasionally be spontaneously created by mutation. StuRat (talk) 13:45, 14 October 2015 (UTC)

People with mental illness often reproduce, and there's at least a chance that the tendency toward mental illness will be passed along. The same goes with any birth "defect", unless of course that defect somehow renders it biologically impossible to reproduce. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:08, 15 October 2015 (UTC)

There are several key things to bear in mind here:

1. Not all birth defects and mental illnesses are genetic diseases - so we have to ignore all the ones that aren't.
2. Many (most?) genetic diseases require that you get at least a matched pair of the same broken gene. So you might find a person with a single copy of the bad gene will exhibit no symptoms and have a 50/50 chance of passing it on to their children. It the odds of having that bad gene are one in a thousand - then the odds of having children with a spouse who ALSO has the bad gene is one in a million - and since each child gets one copy of the gene from each parent, the odds are only one in four that a child will get two copies and thereby suffer the consequences. When the probability of a bad gene causing the owner of it to fail to have children is only one in four million - there is almost zero evolutionary pressure to eliminate it.
3. In some genetic diseases, having one copy of the disease gene turns out to be beneficial - Sickle-cell disease is a great example of this. Having just one copy of the gene grants a person increased resistance to malaria - having two copies compromises the blood's ability to carry oxygen, so without treatment, the victim will die at a younger age than the general population. The genetics of this are interesting because if all of the population had one copy of the gene, then 25% of their children would have the disease - and evolution would select against it. But if sufficiently few people have it to make it rare for children to get two copies of the disease - then evolution will select for those people with malaria-resistance. So evolution both keeps the disease in check and prevents it from being eliminated entirely. Furthermore, the gene is not present in groups of people who come from places where there are no malaria-carrying mosquitoes (because evolution rapidly eliminates it) - but fairly common in people from places where the disease is common (where evolution acts to keep the gene around despite the premature deaths it causes).
4. Many genetic problems are merely trigger conditions that require something else to be present in order to cause a death. Suppose there was a gene that caused babies to die if their mothers were exposed to a very mild toxin found in (say) green tea. Only mothers who drank the stuff during pregnancy would lose their children - and if they didn't, then the gene would be passed on to future generations. Under such circumstances, a mutation that made women find green tea to taste horrible might be the way that evolution 'fixes' the problem - it might not get rid of the bad gene at all! So when a new food craze sweeps the nation, who knows how many new trigger conditions are being tripped on genes that were innocuous in the past? Evolution would take a long time to adapt to a change like that.
5. Genes do mutate - as a result of chemicals or radiation or just simple mistakes in the DNA replication process. So brand new genetic mutations appear all the time - and evolution might easily require hundreds of generations in which to take effect. So if someone gets a mutated gene today that causes lots of early deaths, you might still find it around in the population for a thousand years.

You might argue that it's surprising that we have so many genetic diseases - but you don't know about all of the ones that we've evolved NOT to have. Evolution is very efficient at eliminating very fatal conditions - but we'll probably never know about all of the problems that evolution already cleared up for us.

SteveBaker (talk) 20:42, 15 October 2015 (UTC)

Allotopic expression

It seems like allotopic expression has been receiving a more hopeful treatment lately. An obvious question is whether it is possible to express every gene in the mitochondrion from the nucleus and delete the mitochondrial genome altogether, which might shed some interesting light on aging and other processes. Is anyone attempting such a project? [admittedly, cytochrome c might be a problem because of the apoptosis, but I imagine there should be a way to keep it from being active before transport ...) Wnt (talk) 14:52, 14 October 2015 (UTC)

I do not think it is possible to transfer mitochondrial genes to the nucleus without significantly altering mitochondria, which in practice means that this is impossible. Ruslik_Zero 18:43, 14 October 2015 (UTC)

The basic problem, I think, is that mitochondria (which are essentially bacteria that invaded eukaryotic cells and then were extensively modified) have cell membranes, and their genes form proteins inside those membranes. If you generate those proteins outside the mitochondria, they won't get inside unless they are modified in a special way -- mitochondria have a translocase mechanism for transporting proteins across their membranes, but it only acts on proteins that include special "recognition sequences", as explained in Mitochondrion#Structure. Looie496 (talk) 12:50, 15 October 2015 (UTC)

My apologies! I was thinking of the 5' and 3' UTR approach from [1] for example; I was thinking this was part of the definition of the idea but I suppose not; actually, come to think of it, the protein signal might be needed for things that shouldn't be translated at the cell membrane. I suppose in no case would it be easy, but compared to making a synthetic mycobacterium it doesn't seem all that implausible. And there's always a chance you get the infamous Dorian Gray mouse out of it, though alas, I doubt it. Wnt (talk) 13:08, 15 October 2015 (UTC)

• “Is anyone attempting such a project?” It's one of the Strategies for Engineered Negligible Senescence and thus a goal of the SENS Research Foundation, though I've no idea how actively it's pursued. —Tamfang (talk) 07:11, 17 October 2015 (UTC)

training, meditation, exercise methods to tune hypothalamus into reduced alertness, increased relaxation and sleep state, do they work or pseudoscience

OP want knowledgeMahfuzur rahman shourov (talk) 16:04, 14 October 2015 (UTC)

I don't know about involvement of the hypothalamus, but those methods certainly can reduce stress, which can keep people awake. StuRat (talk) 16:10, 14 October 2015 (UTC)

adrenocorticotropic hormone (ACTH) is secreted by the pituitary and is a major stress/fear/fight-or-flight kind of signal; it causes release of cortisol which is fairly convincingly hazardous to the health long term. Our article says it is stimulated by corticotropin-releasing hormone from the hypothalamus; honestly I don't remember but that sounds about right. So I think CRH is the target of your ministrations. I found a dinky study that claimed that running and meditation increased CRH among runners and mediators,[2] but am loath to claim anything at all from that, except that was the only one that came up in my search. I have little doubt that changing your mental state can change your mental state, but how much is hypothalamus is another question. Wnt (talk) 18:41, 14 October 2015 (UTC)

A380: More efficient at greater speed?

The Airbus A380 article cites this as saying that “the faster you fly [the A380], the more fuel-efficient she gets; when you fly at [Mach] 0.86 she is better than at 0.83.”

Are we talking about fuel used per unit of distance (what else could fuel efficiency mean?) and if so, how could it be true?Hayttom (talk) 21:25, 14 October 2015 (UTC)

Why is it so unbelievable? Surely when the airbus is stationary it's least efficient, and it's most efficient at some particular speed. For the airbus, it seems that speed is mach 0.86. Just like a car, driving a car at 10km/h is less fuel efficient than driving it at 60km/h. Vespine (talk) 21:39, 14 October 2015 (UTC)

'Unbelievable' is a pretty big word. I prefer 'curious'. Wind resistance increases with the square of the speed. Even for cars. (And fuel used per unit of distance for a stationary Airbus, or car, gets you a divide by zero error.) Hayttom (talk) 07:03, 15 October 2015 (UTC)

You can think about it this way: the aircraft's engine is used for two things, (1) providing lift so that the plane doesn't lose altitude, and (2) overcoming air resistance while moving forwards. When an airplane flies slower, air resistance and hence the fuel spent on (2) decreases, but it still has to provide the same amount of lift. Hence the longer the plane is in the air, the more fuel is spent on keeping it aloft, and slower speeds mean more air time. - Lindert (talk) 22:00, 14 October 2015 (UTC)

Jet fuel consumption rates are nontrivial to explain! Have a look at jet propulsion range and thrust specific fuel consumption, for starters. The Airplane Flying Handbook also has a chapter on transitioning to jet powered airplanes. From the section on jet propulsion efficiency: "The specific fuel consumption of jet engines decreases as the outside air temperature decreases for constant engine r.p.m. and true airspeed (TAS). Thus, by flying at a high altitude, the pilot is able to operate at flight levels where fuel economy is best and with the most advantageous cruise speed. For efficiency, jet airplanes are typically operated at high altitudes where cruise is usually very close to r.p.m or exhaust gas temperature limits." In other words, a modern jet engine is literally designed to run as close as possible to thermodynamic efficiency limits (without melting the metal that it is made of). If you run at peak power, you're extracting almost all of the usable chemical energy that can possibly be converted into mechanical energy. Read more about the thermodynamics and the engine efficiency at: specific impulse. Nimur (talk) 22:02, 14 October 2015 (UTC)

Thanks! Hayttom (talk) 07:03, 15 October 2015 (UTC)

Resolved

Re: “the faster you fly [the A380], the more fuel-efficient she gets”: Obviously this is true only up to a point, which I suppose could possibly be it's maximum speed, although this seems unlikely. BTW, supersonic planes tend to be rather inefficient at subsonic speeds, so this is an even more extreme example of the same concept. StuRat (talk) 03:43, 16 October 2015 (UTC)