Wikipedia:Reference desk/Archives/Science/2006 August 8

Cortisone
What causes depletion of cortisone in your body? And what does it mean? --70.40.144.203 00:39, 8 August 2006 (UTC)
 * Where did you hear this, one of those diet pill commericials? --mboverload @ 00:47, 8 August 2006 (UTC)
 * That's stress hormone cortisol, suggested to be what makes you fat. — [  Mac Davis ] (talk)
 * Cortisone is not used up, per se. Instead, it is usually too low when the adrenal gland has been damaged or destroyed, such as in Addison's disease or Waterhouse-Friderichsen syndrome. Alternatively, it may never form (21 hydroxylase deficiency) or may be turned off by taking steroids such as prednisone. When you have too little cortisol (the name for the chemical in your body), things like low blood pressure and low blood sugar result. Hope this helps! InvictaHOG 00:49, 8 August 2006 (UTC)

Solar Dynamo soon?
Today, In a short fun discussion with a professor we talked a little about various types of sci-fi armagedon movies and laughed at their unsupportive / ridiculous events (if you want to call it that). Eventually, one of my peers mentioned about a possible Solar_dynamo happening in the near future (not sure if they're correct). In addition, they mentioned that it "the electricity will go out". I was wondering if that was just a rumor or it could really happen. If so, how devistating can it be? Thanks in advance for the output!


 * Did you read the "solar dynamo" article? If you're worried that the "solar dynamo" might happen soon then be very afraid, because it's already happened.  It is describing a process that is at work in the sun all the time.  Now perhaps what your schoolmates meant was a reversal of the sun's polarity, or whatever, and so um, "causing the electricity to go out."   If they mean that it'll cause everything that uses electricity on earth to stop working, well, that's not what the solar dynamo will do.  71.113.119.102 01:32, 8 August 2006 (UTC)

Hmm... the part about the sun's polarity shifting sounds much more correct. I may have just read the wrong thing on the article of the sun. Thanks for the info! Is there any possibility when this might happen? because unless i have been misinformed again (or taken something out of context) they mentioned it happens every 11 years? --Agester 01:50, 8 August 2006 (UTC)


 * Yes, every 11 years (give or take a few). It is associated with increased solar activity (e.g. solar flares, coronal mass ejections), which can be bad for satellites, but only rarely affects life here on Earth.  It is possible for a very active sun to affect power grids and cause short lived outages, but that generally only happens when the grid is already overtaxed, and mostly at high latitudes where the Earth's magnetic shielding is weaker.  See: geomagnetic storm.  Dragons flight 03:16, 8 August 2006 (UTC)


 * Could we tap into this energy source? DirkvdM 10:07, 8 August 2006 (UTC)


 * Is it worth it for a couple of days every eleven years. Philc  TECI 12:18, 8 August 2006 (UTC)
 * *blink* you are suggesting solar dynamo only exists a few days every 11 years? If you wanted to tap the energy of it all the time, all you would need is a coil large enough to induct the energy.  I will leave coil size up to you (hint, the field exists at the extremities of the sun) --Jmeden2000 15:10, 8 August 2006 (UTC)


 * Ok but the suns magnetic field is on an 11 year cycle, at the end of which it completely breaks down and starts again. Philc  TECI 23:08, 8 August 2006 (UTC)
 * A magnetic field isn't only useful when it changes...

Calculating speed from gravity.
Let's say I drop an object, from the window of the 2nd or 3rd floor, like a ball, and I use a stopwatch to measure the duration of fall. Once the object hits the ground, I stop the stopwatch and now have the time it takes to accelerate via a distance. With the time, using d = .5att (or d = (1/2at^2)), where a = ~32.1 feet/second^2. Plug in time t, and you now have the distance. But is there a way to calculate the speed at which the object hits the ground? (Like in miles/hour). Or am I missing some variables here?

For example, if t = 5.5 seconds, then I would already have reached freefall acceleration of 120 mph. Thanks. NealIRC

There are several ways - a*t gives you the velocity (this assumes no air resistance, as does your calculation). Another way would be to assume conservation of energy - the starting potential energy (m*g*d) = 1/2 * m * v^2. Raul654 01:50, 8 August 2006 (UTC)


 * For a constant acceleration (as with gravity, as long as you neglect air resistance) your final velocity is equal to your initial velocity (zero, if your object is dropped from rest) plus the acceleration multiplied by elapsed time.


 * vfinal = vinitial + a&middot;t


 * Acceleration is the rate of change of velocity with time, right? 32 ft&middot;s-2 tells you that your velocity is changing by 32 feet per second, each second.  Every second that goes by, your velocity changes by 32 feet per second, until your smack into the ground.  (Dang, I wish you guys would use metric...). TenOfAllTrades(talk) 01:55, 8 August 2006 (UTC)


 * TenOfAllTrades is correct; but the just to clarify: time is continuous, e.g. you don't speed up all 32 ft/s  at the end of each second.  You are gradually accruing additional velocity, so you can have fractional seconds.  (after 1.5 seconds, you would have v=48 ft/s ). Nimur 19:57, 8 August 2006 (UTC)

My guess
Is it 9.81 m/s^2?--Light current 02:27, 8 August 2006 (UTC)


 * According to Acceleration due to gravity, it is defined as exactly 9.80665 m/s^2. Raul654 02:46, 8 August 2006 (UTC)

Hey, not bad after 35 yrs not using it! I think I deserve a prize! But I dont think Ill be getting one 8-(--Light current 02:54, 8 August 2006 (UTC)
 * :-) Here Light, I give you this marble, [[Image:The_Earth_seen_from_Apollo_17.jpg|15px]], as reward for remembering Earth's gravity. Dragons flight 03:08, 8 August 2006 (UTC)

Hey thanks babe! I'll treasure it!--Light current 03:16, 8 August 2006 (UTC) Oh I see -- that brings me back to earth 8-))! --Light current 03:19, 8 August 2006 (UTC)

Accurate value
That is if you are at the vertical geodetic datum; the value decreases as your elevation increases. However, if you need that level of accuracy, you're perhaps better off using G anyways... Tito xd (?!?) 02:54, 8 August 2006 (UTC)


 * That value is some kind of average. In St. Petersburg, Florida the actual acceleration of an encyclopedia dropped in a vacuum is closer to 9.79 m/s2. --Lambiam Talk 07:43, 8 August 2006 (UTC)


 * I agree. The acceleration due to gravity is a naturally occurring phenomenon that can be measured, it's not some abstract concept that is amenable to an arbitrary definition.  JackofOz 12:09, 8 August 2006 (UTC)


 * Sure, it's a defined constant, used as a reference value. The actual number will depend on your location and altitude.  It's useful if you need an exact value (this component was stressed under an acceleration of 200 g, the samples were centrifuged at 100,000 g for 2 hours) so that you can make comparisons.  It's just like how one atmosphere of pressure is usually pretty close to (but not exactly equal to) the actual atmospheric pressure at a given place and time on Earth.  TenOfAllTrades(talk) 12:38, 8 August 2006 (UTC)


 * Spooky. Shades of those crazy 19th century Americans who tried to legislate for the precise value of π. JackofOz 22:37, 8 August 2006 (UTC)

Pi
Pi is a whole number equal to pi. Its all the other numbers that are wrong. 9-)--Light current 22:55, 8 August 2006 (UTC)

>> Actually Pi does have an precice value it is equal to 4* the intergal from 0 to 1 of dx/(1+x^2). Most people are just not used to this as a numbering system; never the less it is a precice value--Aaron hart 07:52, 9 August 2006 (UTC)

Exactly my point. Trouble is it makes counting and integers etc a bit difficult. I believe it can alos be expressed as the result of many other integrals not to mention infinite series. 9-(--Light current 13:31, 9 August 2006 (UTC)

>>But back to the real question, it does not only apply to the gravitational value of the earth, Acutally it is the two masses one the earth and the other the object accelerating towards it, the small object acctually accelerates the earth towards it, but this is an old theory, acutally gravity is due to the curviture of space-time due to mass, i.e. the moon accutally travels in a staight velocity through space-time that is curved due to the mass of the earth! This is rather complicated and has is due to the fact that matter in space-time is considered as a perfict fluid thats most important characteristic is its energy distribution. Thus the gravitational behavior of any body is determined by its total energy constent, but this is almost imposible to demonstrate by experimentation--Aaron hart 08:01, 9 August 2006 (UTC). I do not believe that it is totally understood!

Pain Threshold
Is there a way, or are there multiple ways, for a person to increase his or her pain threshold significantly?


 * Do you mean threshold before pain is subjectively experienced, or threshold before you're willing to confess to anything they want to hear? The use of morphine can help, also with the latter. But most analgesics are controlled substances in most countries. There is the gate control theory of pain, which may give some ideas. Also read our article on Pain management. Some people are helped by meditation, others by hypnosis. There are claims that one can train to endure pain, but I've no specific knowledge about the effectiveness. --Lambiam Talk 07:26, 8 August 2006 (UTC)
 * I'm reminded of Lawrence of Arabia, who was able to hold his hand over a lighted candle without flinching. When someone said "Doesn't that hurt?", he said "Of course it does, but I don't mind the pain".  JackofOz 12:06, 8 August 2006 (UTC)
 * Great movie - I believe the quote is "Of course it hurts. The trick is not minding that it hurts"  --Bmk 14:24, 8 August 2006 (UTC)
 * Thanks for the correction. My other favourite (hopefully not mis-)quote about pain is Oscar Wilde: "I can stand anything except pain". JackofOz 22:34, 8 August 2006 (UTC)
 * Did anybody ask the candle "Does't that stink ?" (guess its answer). Any threshold, anyway, is modified by regular use. See sudoku, Mithridate and athletic training.-- DLL .. T 18:31, 8 August 2006 (UTC)
 * No, that's not right. Even when it's utterly frustrating, Sudoku is always pure pleasure.  JackofOz 22:34, 8 August 2006 (UTC)


 * The Buddha was known to be great at not caring about pain. But keep in mind, pain is something your body does to you to keep itself alive. You feel pain from a burn so you don't do it again. You feel pain if you get a rock thrown at your head so you don't let it happen again. — [  Mac Davis ] (talk)


 * A lot of top class martial artists are known for having colossal pain thresholds. So mine would be discipline, its not about not feeling the pain, but knowing its not the pain thats hurting in you. Philc  TECI 22:56, 8 August 2006 (UTC)


 * Well, in that context, the pain is indeed hurting you. But, if you don't want to get kicked in the ribs again, it is best to try to ignore it so you can, as my instructor likes to say, 'move yo' ass out the way of sommin' that's comin' straight atcha! ' That is my take on it. --69.138.61.168 16:46, 9 August 2006 (UTC)


 * You cannot significantly elevate your pain threshold by non-invasive or nor-pharmacological means. But you can quite effectively increase your pain tolerance by physical, cognitive and affective techniques (in addition to taking the drugs which can temporarily increase the threshold for pain). I assume you were asking about tolerance since all the comment above is about it. I see WP has no article describing any of the two quite opposite ways of describing the experience of pain. Hmm, I don't feel like work right now, but I've put up a pain threshold stub-plus for you. And will look to pain tolerance soon. Which should then at least answer your question. --Seejyb 01:01, 10 August 2006 (UTC)


 * But one might ask, is increasing your pain threshold good? What are the negative affects to the body? --Proficient 12:20, 10 August 2006 (UTC)

Nanotechnology - Nano Coatings and ultra thin films - Market trends
Hi All,

Please provide me some information or relevant links to facts and figures related to technology trends and market trends in the area of Nano coatings and ultra thin films in relation to Nanotechnology.

Any help regarding this will be gratefully appreciated.

Thanks, --203.99.212.224 06:04, 8 August 2006 (UTC)Aurnav


 * Have you looked at our article on Nanotechnology? I assure you, it's quite the relevant link. --ByeByeBaby 06:27, 8 August 2006 (UTC)

Yes, I did go thru the article .. however, what I want are facts, figures, graphs, charts etc related to market trends in Nanotech applications ... it should be more business oriented and not just technical information.


 * and it might be a good idea to check the also relevant homework. Xcomradex 08:22, 8 August 2006 (UTC)

Multiple time dimensions
I have a very hard time understanding the concept of multiple time dimensions.

Since our lone time dimension forms a timeline, i suppose having 2 of them could be described as a "timeplane", where the current time could be described with 2 coordinates.

How does an object move through the timeplane? Is its time trajectory random, or can it be controlled? Or does it move in all directions at the same time, creating an infinite number of timelines in the plane?

How is moving forward in the first time dimension different from moving forward in the second one?

Thanks in advance --Angry russian 11:38, 8 August 2006 (UTC)


 * The idea of multiple time dimensions is referred to at 2T-Physics. Itzhak Bars is a (if not the) recognised expert on this.


 * Leaving redlinks to answer questions is pretty unhelpful. Philc  TECI 13:40, 8 August 2006 (UTC)


 * Anon might be referring to Second Temporal Dimension, which is not a very helpful stub. (Sorry but I'm not even going to try to get my head round this question. Hopefully someone brighter will be along shortly.)--Shantavira 15:29, 8 August 2006 (UTC)


 * The idea is inconcievable to us as we are from a universe with a one dimentional timeframe (or timeline in this case) so you won't be able to percieve what the question is referring to if thats what you are trying to do. Since our time line is 1 dimensional, it can only go two ways, and for some reason i don't know, not being a physicist, this side of the speed of light it always goes forwards. Which is fair enough, because being a 1D timeline, if you go from one end to the other, you pass through all the possible timelines, however with a 2D(or more) timeline if you go from one end to the other, either:
 * You miss out a large portion of the possible times,
 * Time periodically jumps back on one of the axis
 * Several times are happening simaltaneously
 * Objects navigate the time plane/space/whatever randomly
 * Or some other obscure thing I haven't thought of, or we cant understand. Someone with a knowledge of these things please comment. Philc  TECI 18:39, 8 August 2006 (UTC)


 * Redlinks can be hellauseful because both "2T-Physics" and "Itzhak Bars" seem very nice google search terms. Dr. Bars' home page suggests another: Two-Time Physics. Sorry, the math is too much for me to write even a stub on it. Sp(2,R) Gauge symmetry acts on phase space, yeah, right, got it, thanks a heap. ;-) Weregerbil 18:30, 8 August 2006 (UTC)

How about if the second temporal dimension is viewed as movement into parallel universes ? For example, if you throw a ball 100 feet in our universe, perhaps you throw it 99 feet in another universe, and 101 in another. As you proceed to parallel universes further in this second temporal direction from ours, you might drop the ball, not even ever have tried to throw it, or you may not exist at all. StuRat 19:54, 8 August 2006 (UTC)


 * At best, this is highly-theoretical physics mathematics; more realistically, it is pseudo-science. Well, good luck wrapping your head around it; I don't know that it will be productive. Nimur 20:06, 8 August 2006 (UTC)
 * Actually it is a protoscience, pseudoscience is something else totally.
 * The parralell universe theory considers all possible universes, not specifically universes with 3 spacial dimensions and 1 time dimension, so inevitably the universe will have been created at some point with more than one time dimension, and as far as I am aware it is impossible for these universes to interact anyway, as there is nothing between them, no spacial or time or any other dimensions, so they are not connected to ours by time or space. 172.206.180.165 20:34, 8 August 2006 (UTC)

Chiropractor titles
A local Chiropractic clinic has opened in my town and the 2 chiropractors there, as stated on the door have BScs and MChiros but before their name the have Dr.

Now, is the title of doctor achieved with the MChiro or have the chiropractors just assumed the title?

Moffo


 * (added title) Please use the "ask a question" link at the top of the page to ask a new question - then your question will get its own topic heading.  In partial answer to your question, you should read the section on "Chiropractic education" in our article on  chiropractors --Bmk 16:21, 8 August 2006 (UTC)


 * May I add that I live in the UK. I apologise about the title thing.


 * I'm fairly sure that they would have to have doctorates. An MChiro is a masters degree, so they wouldn't have got the title of doctor with it, although they may well have obtained the masters before the doctorate (or after, but that's unlikely).  If they aren't really doctors they could get in trouble under the trade descriptions act.


 * If you live in the UK, you may be interested to know that even the majority of UK medical "doctors" aren't real doctors (in that they do not have a doctorate like an Doctor of Medicine). Most have only Bachelor of Medicine and Surgery degrees. They are officially titled "Registered medical practitioners" in the UK but, whether they have a higher doctorate or not, are afforded the courtasy of using "doctor" as an honorary title. That notwithstanding, it is not illegal to call youself a "Dr" without a higher degree in the UK. You can only get in trouble if you try and use the title in a fraudulant way. Whether chiropractors calling themselves "doctors" without a suitable qualification are committing fraud is open to debate.  Rockpock e  t  19:41, 8 August 2006 (UTC)


 * Your comment about the majority of UK doctors not being "real" doctors assumes that the title is supposed to indicate possession of a doctorate. According to, which quotes the OED, the usage of "doctor" as a term for someone who treats illnesses or diseases goes back to (at least) 1377.--71.246.9.240 03:50, 10 August 2006 (UTC)
 * My 'assumption' is based on the root of the word. As our article, Doctor (title), tells us:
 * "Doctor means teacher in Latin. It has been used continuously as an honored academic title for over a millennium in Europe...its primary designation is a person who has obtained a doctorate (that is, a doctoral degree)...From the nineteenth century onward, "doctor" has been popularly used as a synonym for "physician" in Anglophone and many other countries; this term is commonly used as a title of address for physicians, whether or not they hold a doctorate."
 * Put more simply: doctoral degrees, such as Philosophiæ Doctor and Medicinæ Doctor, include the term "doctor" in their title, while Medicinæ Baccalaureus et Baccalaureus Chirurgiæ - the degree conferred on most British registered medical practitioners - does not. Thus, by "real" i meant "in the original sense of the word", not that British medical doctors are fraudulant or underqualified. Apologies for the confusion.  Rockpock e  t  05:23, 10 August 2006 (UTC)

I was surprised when signing on with a new dentist (in the UK) to see that he described himself on his business card as "Dr" so-and-do, despite only having bachelor's and/or master's degrees in dentistry. --rossb 08:11, 10 August 2006 (UTC)
 * General practitioners with only bachelor's degrees call themselves "doctor" in Australia too. The funny thing is that many specialists, who have to be trained medical practitioners first, and many of whom really do have Doctorates of Medicine, insist on being called Mr, not Dr. JackofOz 11:18, 10 August 2006 (UTC)

Cost/Price of an EMD SD40-2 Locomotive in 1972
What was the price tag of an EMD SD40-2 diesel-electric locomotive in 1972, the first year they were offered?


 * I'm going to Google this, only because I am mildly amused by such a question. I wonder if you have already Google'd.  But I am now legitimately curious... did you think anyone on the Reference Desk would know this off-hand?!?  Or did you just want to solicit us to perform the google-search FOR you? Nimur 20:26, 8 August 2006 (UTC)


 * These models cost $190 in 2006. Nimur 20:30, 8 August 2006 (UTC)


 * And I imagine that you were the one who asked the exact same question here. The responses estimate from $100,000 to $500,000. Nimur 20:32, 8 August 2006 (UTC)


 * And according to the IRS, though they insist this is not official, many EMD SD40s are re-built and can re-designated as SD40-2 models for tax purposes. This would significantly reduce the cost. Nimur 20:38, 8 August 2006 (UTC)
 * There's nothing wrong with asking - the reference desk isn't really for giving answers to questions - it's for helping people answer their own questions by pointing them in the right direction. In that spirit, i'm going to link to our insanely detailed article on the EMD SD40-2.  I was rather surprised that we had an article on this, and even more surprised when it didn't mention the price :(  Sorry - I tried --Bmk 20:45, 8 August 2006 (UTC)


 * Sorry. I didn't mean to sound aggressive, I meant to sound surprised.  This is an awfully specific fact; I imagine the only way to find out such a detail is to personally contact a train salesman from 1972.  Even then... Nimur 20:49, 8 August 2006 (UTC)
 * No problem, sorry for the reaction! It is a remarkably obscure fact, as facts on this desk go :)   -Bmk 22:03, 8 August 2006 (UTC)

This fact may seem "obscure" and insignificant. However, it serves as a basis for comparing the cost/price in real terms against current locomotive models, and is therefore fairly important. Any info you can add on this would be greatly appreciated. The nearest I've come to the price is approximately $400,000, but an exact figure would carry more weight.

Moths and 100% Nylon
Will Moths eat 100% Nylon fabric, if it is used as a protective covering for clothing?

Thank you Anna Porter


 * I dont think they like nylon so its a good protector for clothes. Alternatively, you could use a platic carrier bag. I found that works.--Light current 19:17, 8 August 2006 (UTC)
 * Indeed, they won't. It is the hatched larvae that munch on your clothing, which they only do after burrowing inside the wool. A moth won't deposit her eggs on a smooth dense fabric. The larvae cannot digest nylon and need animal hair like wool or felt to survive. --Lambiam Talk 19:25, 8 August 2006 (UTC)
 * ... and that's no myth :--) JackofOz 22:26, 8 August 2006 (UTC)


 * Dont you mean moth? 8-)--Light current 23:35, 8 August 2006 (UTC)


 * No, it is a moth, just not a myth. Pay attention please! DirkvdM 09:10, 9 August 2006 (UTC)


 * Id get that lisp seen to if I were you! 9-)--Light current 13:04, 9 August 2006 (UTC)
 * Lithp? What lithp?  JackofOz 13:30, 9 August 2006 (UTC)

uk Frogs
How long does a small frog grow into its full size (uk)--86.139.143.214 19:41, 8 August 2006 (UTC)


 * I assume since you asked about time in the UK, that you want it in UK units, like fortnights. :-) StuRat 19:57, 8 August 2006 (UTC)


 * HEY now, no anti British comments please! 8-)--Light current 22:12, 8 August 2006 (UTC)


 * Did I get off on the wrong track ? (Or should I say the wrong dual carriage-way ?) :-) StuRat 04:01, 9 August 2006 (UTC)


 * Well, you seem to have have put your foot metre in it. DirkvdM 09:25, 9 August 2006 (UTC)


 * What a display of xenophobic ignorance. Philc  TECI 11:26, 9 August 2006 (UTC)


 * First I'm being called anti-xenophobic and now xenophobic again. At least I'm wonderfully unpredictable, just the way I like myself. DirkvdM 18:35, 9 August 2006 (UTC)


 * No, no its all done the best possible taste as Kenny Everett plaing 'Cupid Stunt' used to say.--Light current 14:20, 9 August 2006 (UTC)


 * Frog life cycles are discussed on the main page. Specifically, "Most temperate species of frogs reproduce between late autumn and early spring. In the UK, most common frog populations produce frogspawn in February, although there is wide variation in timing. Water temperatures at this time of year are relatively low, typically between four and 10 degrees Celsius. Reproducing in these conditions helps the developing tadpoles because dissolved oxygen concentrations in the water are highest at cold temperatures. More importantly, reproducing early in the season ensures that appropriate food is available to the developing frogs at the right time."  This suggests between 4 to 6 months from fertilization to frog-form. Nimur 20:01, 8 August 2006 (UTC)


 * Which is between 8 and 10 fortnights ; but the tadpole life may be quite long before you have a perfect small frog. -- DLL .. T 20:10, 8 August 2006 (UTC)


 * 8 and ... 12? Nimur


 * I get 4 to 6 months = 8.5 to 13 fortnights. StuRat 21:40, 8 August 2006 (UTC)


 * The French don't thrive in the UK. Even when they're small. DirkvdM 09:25, 9 August 2006 (UTC)


 * No they live in France. Your speech impediment is getting worse! 9-)--Light current 14:10, 9 August 2006 (UTC)


 * And now I'm being confused with JackofOz. I didn't plan on being that unpredictable. DirkvdM 18:35, 9 August 2006 (UTC)


 * No I dont think so. Did you not write this lisp:
 * No, it is a moth, just not a myth. Pay attention please! DirkvdM 09:10, 9 August 2006 (UTC)
 * --Light current 00:08, 10 August 2006 (UTC)
 * --Light current 00:08, 10 August 2006 (UTC)

I officially declare this "irrelevant answer day" on the Science ref desk. I haven't carefully surveyed the other posts, but on this one there are about ten irrelevant comments for every helpful one. :) don't stop, though.  It's much more fun to read. --User:bmk.
 * I'm much, much sexier than Dirk. Not hard to tell us apart.  JackofOz 11:09, 10 August 2006 (UTC)


 * Actual attempt at answer Several years, I think. We used to have lots of frogs in the garden and there seemed to be several sizes of frog reflecting different years. Hundreds of the tiniest frogs, a few at various medium sizes and 2-5 large frogs. Judging by the number of sizes, and making a few (possibly unfounded) assumptions, I'd say a frog takes about 5-8 years to become those really big frogs. Skittle 13:50, 10 August 2006 (UTC)

Incidence of Down's Syndrome decreasing?
The article on Down Syndrome mentions that a kind of 'eugenics by abortion' is happening, where parents undergoing prenatal genetic screening are opting to abort rather than give birth to a Down's child. I've been wondering if this has resulted in a decrease in the incidence of Down's children in the world. In the future, will Down's and other testable genetic disorders be seen only in families that are members of religions that are against abortion? Adambrowne666 23:09, 8 August 2006 (UTC)


 * Eeep. This is certainly a touchy subject. I'm sure somehow, someone's response will infuriate the internets :/    Anyway.  I wonder if your hypothesis is accurate.  It does makes sense to me - not just for Down Syndrome, but for numerous other genetic ailments.  I wonder if 'eugenics by abortion' is a loaded phrase; but, yes, I tend to agree that this effect would occur, weeding out genetic problems in family-lines who would prefer no child to a diseased child.  Another factor is the recessive gene effect (I'm not a biologist so I don't know if this applies to Down Syndrome, but certainly might for other diseases/conditions).  It's possible that bad genes are passed through the hereditary line without ever expressing themselves.  Perhaps this could continue for many generations; but the rate of occurence would be decreased.  I guess a followup question might be whether it is testable. Nimur 23:44, 8 August 2006 (UTC)


 * Abortion would have an effect on the prevalence, but not the incidence, of Downs Syndrome. There's no "gene" for Downs Syndrome, it results from a chromosomal abnormality, and that abnormality generally arises anew rather than being inherited from someone who already has it. On the other hand, a societal trend to have children early, rather than late, in life, would decrease both incidence and prevalence of Downs Syndrome. - Nunh-huh 23:52, 8 August 2006 (UTC)


 * While Down's Syndrome is genetic, I don't think it's normally inherited. That is, it's caused by an error in chromosome replication in the sperm and ova of genetically healthy mothers and fathers.  However, the tendency toward having errors in chromosome replication may indeed have a genetic component, so this trait could be reduced by abortions.


 * In a recessive genetic disorder, in unrelated mothers and fathers, the rate of appearance of the disease (phenotype), is proportional to the square of the portion of people with the recessive gene (genotype). That is, if 1 in 10 people carry the gene, then 1 in 100 will have the disease. StuRat 23:55, 8 August 2006 (UTC)


 * Is it impossible that a tendency to develop chromosomal abnormalities can itself be inherited? -Wfaxon 00:06, 9 August 2006 (UTC)

[ec]
 * For DS in particular, there's probably not a large "eugenics" effect simply because it's not a simple genetic trait, such as a sickle cell-type recessive mutation, but rather a trisomy of chromosome 21. DS patients rarely have children, so that pathway of genetic perpetuation is limited.  It's very possible that parents of DS children have other genetic polymorphisms that may increase the incident of a nondisjunction event, and if these parents produce other viable children those polymorphisms will persist in the population.
 * The most important risk-factor associated with DS, however, is maternal age at conception. Modern technology has allowed far more 35+-year old women to have children, and far more reporductively-challenged couples to conceive.  If I were to hazard a guess, the increased number of children born to older mothers probably offsets the screening effects, but I've not found anything on PubMed just yet that supports my guess or with a clear indication on increased or decreased prevalence of DS. -- Scientizzle 00:07, 9 August 2006 (UTC)

The total prevalence for trisomy 21 is increasing as more older women are having children, in some places as much as 2-fold over the last 20 years. However, there is a divergence between live births and diagnosed cases (At least in European areas with abortion) due to pregnancy termination. One recent study showed that 77% of Parisian fetuses diagnosed with trisomy 21 were aborted. The reference is "Dolk H, Loane M, Garne E, De Walle H, Queisser-Luft A, De Vigan C, Addor MC, Gener B, Haeusler M, Jordan H, Tucker D, Stoll C, Feijoo M, Lillis D, Bianchi F. Trends and geographic inequalities in the prevalence of Down syndrome in Europe, 1980-1999. Rev Epidemiol Sante Publique. 2005 Nov;53 Spec No 2:2S87-95. " InvictaHOG 00:30, 9 August 2006 (UTC)

Though I don't think this applies at all in the case of DS, one of the stranger side-effects of prenatal abortion is that you have a high chance for a "dysgenic" effect (if we want to use those terms) because heterozygous populations can reproduce more often without getting double-recessive children. In Cyprus, for example, prenatal testing drastically allowed for the decrease in the prevalence of thalassemia (a condition similar to sickle-cell anemia) through pregnancy termination. Prenatal testing though has allowed heterozygous parents to have more children than the would otherwise: children with the double-recessive condition not only drained their family resources, but made them very anxious about having more children; after it was possible to have children without the double-recessive, parents felt more free to have more children. The irony here is that they've basically taken the Mendelian ratios and knocked the double-recessive option out of the picture: now the only options are AA, Aa, and aA. Which means that 2/3 of the children actually born are probably heterozygous, and there are probably more of them due to the larger family size, which a eugenicist of the old school would see as an issue (you are in fact leading to an increased incidence of the trait in the population than you would otherwise, even if the prevalence is decreased). At least, that's my interpretation of it. (I am not a eugenicist, mind you; I don't necessarily think that one needs to lower incidence if working on prevalence will do the job.) --Fastfission 01:11, 9 August 2006 (UTC)

Excellent answers, thank you. Adambrowne666 04:00, 9 August 2006 (UTC)
 * Down syndrome can be inherited - see Robertsonian translocation. Increases in "spontaneous" nondisjunctions (as noted above, due to older women giving birth) may have a larger effect on the prevalence. But inherited DS cases should be going down due to abortions. zafiroblue05 | Talk 04:25, 9 August 2006 (UTC)
 * Familial Down syndrom, as our article says, only accounts for 2-3% of all cases of Down Syndrome. There is still no reason to suspect that inherited incidence would go down via abortions (again, since most cases of DS are not caused by people exhibiting DS—the translocation would still presumably be passed along in the non-aborted, non-DS children who are born to such families). Indeed it may even rise, based on similar to logic to what I posted above. It is one of the grim ironies of "eugenics" that attempts which focus on prevalence may lead to solutions of increased incidence. --Fastfission 16:18, 9 August 2006 (UTC)


 * I find it curious that the questioner apparently assumes that anyone who discovered their in utero child had Down Syndrome would automatically want to end the pregnancy, unless a religious conviction precluded that. I could foresee many pro-choice people choosing to carry such pregnancies to term, perhaps based on experience with Down children, or an attachment formed with the child before its birth. --Ginkgo100 talk · contribs · e@ 18:18, 9 August 2006 (UTC)


 * I didn't assume that at all. I was referring to the phrase 'eugenics by abortion' in the Down's article, and suggesting it as a tendency that might reveal itself over several generations. Adambrowne666 21:28, 9 August 2006 (UTC)


 * And the numbers are very high, even though DS is not the worst thing that someone can be born with (relatively long life-expectancy, reputation for kindness and gentleness, able to live independently after some training, etc.), and most people would not consider it to fall under "life not worth living". One of the reasons is likely that it is one of the better known genetic syndromes and so easily identifiable (visually) with mental retardation than many other genetic diseases. --Fastfission 01:05, 11 August 2006 (UTC)


 * Secondary question: I've read in a few places (articles in newspapers) that the rate of miscarriage due to amnicentitis (sp) plus the number of children incorrectly identified as having Down's Syndrome was greater than the number correctly identified. Is this true? I can't find the right sort of sites to tell me. If it is true, might not to tendency to check for/abort Down's Syndrome be selected out faster than any genetic tendency for the syndrome itself? Skittle 13:46, 10 August 2006 (UTC)


 * I don't understand the last part of it — are you assuming that the tendency to get prenatal testing done is somehow genetic? I find that pretty unlikely, even with a very flexible notion of inherited psychology; almost all of the key aspects are blatantly cultural and institutional. In any case, prenatal testing and abortion does not necessarily decrease the number of children a family might have; as I mentioned earlier, in many cases it increases the number by allowing parents with at-risk genetics to feel comfortable in increasing their family size without taking on the burden of raising a child with genetic illness. The miscarriage rate for amniocentesis is about 1 in 100. The chance of having a fetus with Down's syndrome in a woman 35 and older is about 1 in 385. I don't know the numbers for "correctly" and "incorrectly" (I'd want to look at numbers like that very carefully because it would be very easy to get strange methodologies on that). However amniocentesis is used to screen more than just DS, so looking at just the DS numbers wouldn't necessarily tell you much. --Fastfission 01:05, 11 August 2006 (UTC)