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

= July 14 =

Penis in vagina
Why is "penis in vagina" sex so ubiquitous in nature compared to fertilizing eggs externally or other methods of non-preventative procreation?


 * Cause it's a lot more fun. Contact  Basemetal   here  17:31, 14 July 2015 (UTC)


 * That reply is of course completely and utterly backwards. It is 'fun' because if it wasn't, animals wouldn't engage in it, and would thus fail to reproduce. AndyTheGrump (talk) 17:39, 14 July 2015 (UTC)


 * And of course many animals don't need to do anything of the sort. Penis-in-vagina sex is in no way necessary for a viable population, as demonstrated by my many refs below. SemanticMantis (talk) 18:59, 14 July 2015 (UTC)


 * There is obviously a benefit to letting a baby grow in the womb for a while instead of laying an egg. So, in that case, how else do you expect the egg to be fertilized? 209.149.113.136 (talk) 17:38, 14 July 2015 (UTC)


 * As noted below, the male can just hand the female a sperm packet (an entirely different way to deliver one's package). StuRat (talk) 20:11, 14 July 2015 (UTC)


 * You're really missing out on the wide wide world of sex! In fact, the way humans procreate not the norm. First let's get plants out of the way - pollination uses no penis nor vagina, and often involves a second species pollinator as an intermediary.
 * For animals - did you know that squid use a special arm called a Hectocotylus to inseminate females? And then there's many things that use Spermatophores - a salamander puts a little sac of sperm down, then does a mating display, and if the female likes it, she'll take it in to her body. Of course most bony fish use external fertilization, as do many amphibians, corals, protozoans, etc.
 * The Bdelloid rotifer has some of the weirdest "sex" - they have no males, only females, and they can incorporate DNA of their dead sisters when rejuvenating after dessication! Discover magazine couldn't resist a little anthropomorphic language, and called them Lesbian Necrophiliacs
 * Then there's the bedbugs and other invertebrates that use traumatic insemination - the females don't have anything like a vagina, and a male just sort of stabs in to the abdominal cavity. And while we're on the topic of insect genitals, they don't have penises, they have Aedeagus, which is a rather different thing altogether.
 * Every male hymenopteran is born from an unfertilized egg! That's part of the fun of haplodiploidy.
 * The Amazon_molly reproduces solely through gynogenesis - a male (of a different species) is required, but his sperm do nothing! Then there's the very common Parthogenesis, which leads to things like many female aphids being born pregnant with another female - no sex required.
 * There are many other strange tales of sex and nonsexual reproduction in the living world, but hopefully this gives you a better feel for the variety of things out there that can get the job done just fine. While there are many benefits to internal fertilization and live birth that result from penis in vagina copulation, that form is not the norm, neither by number of species nor by number of practitioners. SemanticMantis (talk) 18:57, 14 July 2015 (UTC)


 * It might be the most common, if you look at total biomass of animals that engage in internal fertilization (since that would be "heavily weighted" towards larger animals) versus other forms of sexual reproduction (since that leaves out most microbes). StuRat (talk) 20:10, 14 July 2015 (UTC)
 * Nope. Good thing to think about, but terrestrial insects have more biomass than terrestrial vertebrates, and they don't have penises. Just ants alone have about the same biomass as humans do. And that's not even mentioning huge amounts of bony fish and marine invertebrates, compared to the very few marine animals that practice internal fertilization. Biomass_(ecology) has some info, but could use some expansion. I'll buy that PIV copulation is the most common method of fertilization among terrestrial vertebrates (by species number, individual number, biomass, etc), but that's about it. SemanticMantis (talk) 20:36, 14 July 2015 (UTC)


 * More variety that I should mention - most birds don't have anything like a mammal penis - see Pseudo-penis and cloaca. Spiders use another type of specialized "arm" for insemination - the Pedipalp. SemanticMantis (talk) 21:25, 14 July 2015 (UTC)

MAF sensor disconnection
Most cars (for some time now) are equipped with a mass air flow sensor I know some cars have a MAP sensor but my question is only in regards to vehicles with MAF sensors. Some vehicles will still run with the MAF sensor disconnected while others will not run at all with the MAF sensor disconnected. Why is this? Void burn (talk) 13:57, 14 July 2015 (UTC)


 * The MAF is used to tell the computer how much air is coming in. If it is disconnected, the computer gets no signal. So, the computer could be programmed to assume "average" air flow and then send an "average" amount of gas to the engine. Or, the computer could be programmed to assume "no" air flow and then send "no" gas to the engine. It is really up to the engineers to decide what to do when the MAF sensor isn't sensing anything. 209.149.113.136 (talk) 15:35, 14 July 2015 (UTC)


 * I would imagine that it would be better engineering to program the computer to assume "average" Stoichiometry so that in the event the MAF sensor stops working the vehicle will still drive until the MAF can be repaired. Seems like this should be an industry standard if reliability is desired. Void burn (talk) 17:16, 14 July 2015 (UTC)

In the interests of robustness the engine will attempt to estimate the MAF from the throttle plate angle and the rpm, if the MAF sensor fails. Greglocock (talk) 01:05, 15 July 2015 (UTC)

How can you determine the percentage some feature is determined genetically?
What scientific methods besides comparing twins are useful to tell the percentage that genes plays in a feature? For example, what's the % of our height, intelligence, that's genetically determined. Or how do genes increase the chances we develop some illness like Parkinson or Alzheimer's.--Scicurious (talk) 23:12, 14 July 2015 (UTC)


 * You're right that twin studies are an important tool. Other than that see Disease_gene_identification - now heavily influenced by genomics. There's some info and refs at Nature_versus_nurture, but it's not a very good section. Make sure you read the section on IQ in that article and we have a whole article on Heritability of IQ. Lots of work is also done with model organisms - Knockout_mouse is a very common and popular tool. SemanticMantis (talk) 00:29, 15 July 2015 (UTC)


 * Those are some general methods; for your specific questions, see Parkinson's_disease and Parkinson's_disease. The "percent influence" of genetics is hard to quantify, and my understanding is that each research project will operationalize that concept for each specific question, but there are some general approaches discussed at Heritability. The claims in those disease articles both have refs to the academic literature, if you don't have access you can often find reprints by googling the title, or you can ask for a copy through WP:REX. You may also be interested in List_of_genetic_disorders. SemanticMantis (talk) 00:39, 15 July 2015 (UTC)


 * You must have an inherited tendency to repeat Parkinson's_disease. :-) StuRat (talk) 00:46, 15 July 2015 (UTC)
 * Right, Alzheimer's_disease. SemanticMantis (talk) 01:02, 15 July 2015 (UTC)

Some evidence can be gleaned by looking at two large and genetically similar populations in different environments. For example, comparing cancer statistics within China to cancer statistics amongst Chinese immigrants to the United States, as was done in this study. It's conceptually similar to a large-scale twin study. Someguy1221 (talk) 02:56, 15 July 2015 (UTC)


 * "For example, what's the % of our height, intelligence, that's genetically determined." Is it true that the characteristics of genes (or the characteristics that give rise from genes) are largely determined by environmental variables? Void burn (talk) 17:16, 15 July 2015 (UTC)


 * The phrase "explained by" is sometimes seen in popular literature that presents statistical arguments. I view such vagueness with great suspicion. One of the meanings it might have is discussed in Cross Validated. Jim.henderson (talk) 17:55, 15 July 2015 (UTC)
 * Oh. We do have an article "Explained variation" with appropriate criticism. Jim.henderson (talk) 18:00, 15 July 2015 (UTC)