Wikipedia:Reference desk/Archives/Science/2007 October 14

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October 14

Maximum limit of kinetic energy?

Hey guys! So i was daydreaming today and i thought if absolute zero exists is there an upper limit to the amount of energy a particle can have? Thank you very much for your time!

24.88.103.234 02:42, 14 October 2007 (UTC)Timothy

A greatly simplified way to think of it is that absolute zero is all mass and no energy. The speed of light is all energy and no mass. So, those are your two opposites. From there, you can get into the particulars that break down the simplicity into a muddy mess of conflicting areas of science. -- kainaw™ 02:51, 14 October 2007 (UTC)

That's a level of simplification even I would never go to...In short, no. Someguy1221 04:13, 14 October 2007 (UTC)

But it is true that the speed of light sets an upper limit to kinetic energy, right? DirkvdM 10:11, 14 October 2007 (UTC)

Short answer, no. And that's exactly the reason for the odd mass increase of the accelerated particle when it approaches the speed of light. You 'add' energy to the particle, since it can't store the extra energy as speed, it stores it as extra mass. --Taraborn 14:21, 14 October 2007 (UTC)

Not really. Kinetic energy = 1/2mv, so (ignoring common sense) if you had a mass travelling at c, you could simply have another mass slightly greater than double that of the first travelling at half the speed and you'll have a higher kinetic energy. You can set a maximum theoretical kinetic energy for any specific object, but the maximum possible kinetic energy would be the entire mass of the universe travelling at the speed of light, which is a ridiculously large and pointless number. GeeJo ^(t)⁄_(c) • 10:37, 14 October 2007 (UTC)

Firstly, it's 1/2mv², secondly, that is a formula of classical mechanics, false in special relativity, and so is invalid for large speeds. In SR, the kinetic energy of a body of rest mass m and speed v is given by

$E_{k}=m\gamma c^{2}-mc^{2}={\frac {mc^{2}}{\sqrt {1-v^{2}/c^{2}}}}-mc^{2}$

And so, as the speed of a massive body approaches c, its kinetic energy approaches infinity. Thus c does not provide a very interesting upper bound. (note this does not apply for photons, which actually travel at c but have zero rest mass). Algebraist 10:54, 14 October 2007 (UTC)

<after ec, before seeing Algebraist's response>The relativistic kinetic energy of an object with rest mass m traveling at velocity v (in a given inertial frame of reference) is

$E_{k}=m\gamma c^{2}-mc^{2}={\frac {mc^{2}}{\sqrt {1-v^{2}/c^{2}}}}-mc^{2}$

This is approximately ${\frac {1}{2}}mv^{2}$ when v is small compared to c. However, as v approaches c, E_k is unbounded - it has no upper limit. What this means in practice is that no matter how much energy you pump into an object, it will never reach the speed of light. This is sometimes expressed by saying that the energy increases the object's relativistic mass or inertial mass $m\gamma$, and so makes it "harder to accelerate". Gandalf61 11:00, 14 October 2007 (UTC)

Uh oh, I just thought of something. If photons are all energy and no mass, what is their temperature? I mean, if more photons in an area means more energy (and thus higher temperature), what if you could measure the temperature in a photon? Since temperature depends on the amount of photons (particularily heat) in a certain amount of space, what would be the temperature of one photon? If there is no upper limit, would it be infinity? What if you could squueze a huge amount of photons (just photons) into an extremely tiny space, is it possible for the photons to be so crammed that they create their own mass and gravity? Also, if they had no mass, why don't they float away from gravitation? Is there such thing as an antimatter photon? If there was, if one touched a matter photon, wouldn't it create either no energy at all, or only the amount of energy already in the photons, because E=MC2 relies on mass of the object? Thanks. ~AH1^(TCU) 20:30, 17 October 2007 (UTC)

Wow, that's a lot of misconceptions in a row. I'll see how many of them I can dispel. First of all, temperature is a concept of thermodynamics and statistical mechanics, which only makes sense if there are a large number of particles with a certain statistical distribution of energy. One particle does not have a temperature, only an energy. So one photon does not have a temperature, but a large number of photons can have a temperature if they follow a special distribution called Planck's law. For example, the light from an incandescent light bulb has a temperature (it is equal to the temperature of the filament), but the light from a fluorescent lamp does not (because the spectrum is quite different, having discrete spikes for the different phosphors rather than a smooth curve). The light from a fluorescent lamp has a non-thermal distribution, because it is not in thermal equilibrium with itself (which is possible because the photons don't exchange energy with each other).

The thing you describe next is called a geon. It's unknown whether they are stable in theory, and they certainly haven't been observed.

I'm confused why you ask "why don't they float away from gravitation?". If you shine a flashlight into the night sky, the light does "float away from gravitation". Perhaps you're asking why light follows a curved path in a gravitational field? Well, that's not true either. Light follows a geodesic, which is the straightest possible path in the curved spacetime of general relativity.

The photon is its own antiparticle, which simply means the total number of photons is not a conserved quantity. Anyway, photons can't "touch" because light doesn't interact with other light, only with electrically charged particles (photons are uncharged). So photons cannot annihilate with each other. —Keenan Pepper 14:30, 18 October 2007 (UTC)

Redox reactions

I know that oxidation is loss of electrons and reduction is gain of electrons. I also know that an oxidant gains electrons whilst a reductant loses electrons.

Yet I am a bit confused about the terms (1)"oxidising strength", (2)"reducing strength", when something is (3)"oxidised", when a molecule (4)"oxidises" something else, when something is (5)"reduced" and when something (6)"reduces" something else.

I think that "oxidising strength" refers to the ability for something to act as an oxidant whilst "reducing strength" refers to the ability for something to act as a reductant. Yet I'm not completely certain.

Could somebody please define clearly the 6 above terms. (You can refer to the words oxidant, reductant, oxidation and reduction in the definition as I am confident with these terms.)

Thank you very much. —Preceding unsigned comment added by D3av (talk • contribs) 09:28, 14 October 2007 (UTC)

The oxidising strength is the tendency to oxidise - a very strong oxidant may oxidise a weaker oxidant that would usually be reduced in a reaction and not oxidised - the same goes for a concept of reducing strength - you already have the meaning of 3,4,5,687.102.82.26 17:51, 14 October 2007 (UTC)

The Redox page might be useful…besides being "yet another explanation of the ideas" (sometimes one wording just sinks in better than another), it puts them in context and explains the reactions. Memorizing terms is pretty useless without knowing what they really mean and how they work in the real world. DMacks 18:57, 14 October 2007 (UTC)

Thanks for the reference. I found what I needed on the Redox page. D3av 11:31, 15 October 2007 (UTC)

Cyanide Vs. CO

Though Cyanide and CO are both strong ligand, why is there a difference in their mechanism of toxicising the human body? —Preceding unsigned comment added by Curieous (talk • contribs) 13:51, 14 October 2007 (UTC)

See Cyanide: Mechanism of toxicity and Carbon monoxide poisoning. Xn4 18:52, 14 October 2007 (UTC)

cyanide would almost certainly poison in the same manner as CO, but there is (according to the experts) yet another way in which CN can poison.. If this pathway wasn't available to CN, then cyanide would still be poisonous in the same manner that CO is. (The two compounds CN- and CO are isoelectronic and would be expected to have very similar behaviour

A side question that arises is why doesn't CO poison in the same way in which CN- poisons87.102.82.26 20:35, 14 October 2007 (UTC)

The short answer is that their chemistry is different, so they affect certain vital systems more effectively than others. Even if the substance affects several vital systems it is the one that causes you to die the fastest that is officially the cause of death. For example, if your head gets cut off, it is lack of oxygen to the brain that kills you the fastest (in seconds) rather than lack of glucose, so the cause of death is lack of oxygen although both separately would have killed you.

The long answer is that the "cause of toxicity" is a combination of which cellular process reaches the failing point the soonest after the substance is introduced to the body (usually one with a low concentration of the substance needed to cause critical failure) coupled with the time it takes to die from that failure. Carbon monoxide and cyanide have sufficient chemical difference so that they affect different vital cellular processes much more effectively thus causing the difference in mechanism of toxicity witnessed. Although the compounds are isoelectronic, the overall charge and the distribution of charge are not identical.

• Carbon monoxide is an overall neutral molecule with a slight negative charge on the carbon and a partial positive on the oxygen.
• The cyanide ion is overall negatively charged with the Electrostatic potential surface model on the cyanide page suggesting the negative charge is spread around to both atoms of the cyanide with the more-electronegative nitrogen hogging more of the negative charge.
• These compounds have different bond lengths and atom sizes.

Enzymes are "finely tuned" for their normal mode of operation, with the side effect that small differences in the chemistry of potential inhibitors can drastically change the magnitude of the inhibition.

Now, to get to the nitty gritty. For the sake of this question I will assume a large fatal concentration of the compounds are being inhaled continuously.

• Carbon monoxide poisoning

CO binds to hemoglobin very effectively, so most of it getting into the body will probably stick to hemoglobin and less will be available to muck around with other enzymes. Even if carbon monoxide is binding to many different enzymes in various life supporting pathways, the first pathway that will reach its failure point is the oxygen transport system due to carbon monoxide outcompeting oxygen on the binding site of hemoglobin. Death by lack of oxygen occurs in several minutes so the time until death after the failure point is fairly quick, making it the primary cause of toxicity.

• Cyanide poisoning

Cyanide doesn't bind to hemoglobin as efficiently as CO does, so more of it will be available to muck about with other vital enzymes. Cyanide happens to bind very efficiently to the enzyme cytochrome c oxidase, vital to the production of ATP (which is in high demand in the heart and nervous system). It takes much less cyanide to bind to bind a fatal amount of cytochrome c oxidase than a fatal amount of hemoglobin, so even if the majority of cyanide is stuck to the hemoglobin, the system that reaches it's "fatal concentration" first will be the ATP pathway. Death by lack of ATP to the heart/central nervous system is also fairly quick; the article cyanide says several minutes for high doses, similar to the time to death caused by lack of oxygen. Therefore the cause of death and primary means of toxicity for cyanide poisoning is binding to cytochrome c oxidase and causing a failure of the ATP pathway in the heart and nervous system.

Hoped that helped. If anyone has anything to add please do so. Sifaka ^talk 05:32, 15 October 2007 (UTC)

If possible I'd like to see equilibrium constants for CN/CO Haemoglobin - it the bit about "Cyanide doesn't bind to hemoglobin as efficiently as CO does" - as having a little chemistry I'd find that suprising - but I was never expert in biological systems..83.100.255.190 10:04, 15 October 2007 (UTC)

Also at Cytochrome c oxidase ref 1 - says CO also inhibits the enzyme - is it possible that the CO page is wrong/out of date?83.100.255.190 10:07, 15 October 2007 (UTC)

Would it be truer to say that CO/CN poisoning is in fact due to both pathways? (I'm no biochemist - it's a question.not my 'theory')83.100.255.190 10:27, 15 October 2007 (UTC)

• • Just have a look at this excerpt from the CO article:-

Toxic mechanism:- The precise mechanisms by which toxic effects are induced by CO are not fully understood.

Carbon monoxide binds to hemoglobin (reducing oxygen transportation), myoglobin(decreasing its oxygen storage capacity), and mitochondrial cytochrome oxidase (inhibiting cellular respiration)#

So,may be it justifies the above discussion that though multiple paths are available,the declared path will be the one which is the fastest.

However,the above excerpt says that the mechanism is not fully understood...could someone mention the complications involved in it? --Curieous 08:52, 16 October 2007 (UTC)

microscopy

when the slide is moved down in what direction does the image move —Preceding unsigned comment added by 99.226.126.42 (talk) 14:43, 14 October 2007 (UTC)

Think: Which way is the lens moving relative to items on the slide? --Mdwyer 15:49, 14 October 2007 (UTC)

It depends on the type of microscope.... TenOfAllTrades(talk) 16:20, 14 October 2007 (UTC)

For the type of microscope often used in school teaching labs, the image is inverted, see this manual, page 26. --JWSchmidt 20:02, 14 October 2007 (UTC)

When light enters a microscope's objective lens, light from the lower part of the slide will hit the upper part of the lens, travelling upwards. Light from the upper part of the slide will do the same and hit the lens' lower portion. Of course, the same is true of light from all other directions; it will strike the lens in a position opposite to the object's direction.

This will cause the image to be inverted. So, in which direction will an inverted image move if the slide is moved down? --Bowlhover 04:45, 16 October 2007 (UTC)

Effects of long term usage of asthma medication

I'm just wondering if there are any known adverse effects to long term usage of asthma medication. In particular inhalers such as Duovent. Thanks :) 84.197.59.250 15:16, 14 October 2007 (UTC)

Take a look at the page for the active ingredients: fenoterol and Ipratropium. Both of those articles are kind of short, so you may want to then feed those names into Google. --Mdwyer 15:47, 14 October 2007 (UTC)

Long term inhaled steroid use has risks of glaucoma and cataract formation.

Atlant 16:18, 15 October 2007 (UTC)

Transport Phenomena

While browsing today in WIKIPEDIA, I came across the entry TRANSPORT PHENOMENA. I notice that our book TRANSPORT PHENOMENA, by Bird, Stewart, and Lightfoot (Wiley, 1960) has been cited. Actually there is a 2002 edition as well as a 2007 "Revised Edition." These later revisions should really be cited, since the 1960 edition is now 47 years out of date! R. B. Bird, University of Wisconsin —Preceding unsigned comment added by 128.104.178.123 (talk) 18:03, 14 October 2007 (UTC)

First of all, this is not the place to grovel about out-of-date information. Secondly, the most likely cause of the 1960 ed. being cited is that no one who contributed to the article has the 2002 or 2007 editions. NASCAR Fan24^{(radio me!)} 18:16, 14 October 2007 (UTC)

Be nice. And nobody "groveled". I copied the original message to the article's talk page. --Milkbreath 18:19, 14 October 2007 (UTC)

Guess I did bite them there. I just get mad when people don't use things for their intended functions. To Professor Bird: You may change any out-of-date information in the article. You may want to read WP:CITE to learn how to cite a book. NASCAR Fan24^{(radio me!)} 18:22, 14 October 2007 (UTC)

Some people in academia are too busy to edit, feel they have a conflict of interest or they are just unfamiliar with the wiki concept. I've had people send me email about page content problems in Wikipedia when they could have just taken a minute and fixed the problem by editing the page. "when people don't use things for their intended functions" <-- See Murphy's law. --JWSchmidt 19:45, 14 October 2007 (UTC)

There would be an air of impropriety with the author of a book citing his own work on Wikipedia (although in this case, I doubt anyone would object). It makes sense to have someone who is already an active editor of the article make the change. So the best procedure would be to post this kind of note to the talk page of the article (which Milkbreath took care of)...and if that doesn't produce a result, look at the edit history of the article and ask some of the most active editors directly via their talk pages (or email addresses if they provided them). SteveBaker 21:41, 14 October 2007 (UTC)

• Dr. Bird, I would like to apologize on behalf of polite Wikipedians everywhere for the unmerited incivility you were shown above. It's absurd that an obviously-qualified editor offering input should be treated so rudely. --Sean 15:35, 15 October 2007 (UTC)

  I second this apology. Dr. Bird deserves a more detailed explanation and I have a request, so here goes: anyone can edit, but must cite sources. The original editor had access to the earlier edition, but not to the later one, and therefore could cite it: you must not cite a work unless you actually read it and used it. If another editor (such as Dr. Bird himself) has access to the newer edition and is willing to verify that facts in the article are supported by the newer edition, then that editor is welcome to change the article to use the newer edition. Please help us. Thanks. -Arch dude 15:54, 15 October 2007 (UTC)

Spectroscopy of elements

If spectroscopy of molecules reveals the frequency at which their bonds resonate what is it the spectroscopy of the elements represents, the resonance of the subatomic particles, i.e., protons and neutrons and electrons, within the atom? Clem 18:35, 14 October 2007 (UTC)

NMR and EPR are types of spectra that analyze resonance of nuclei and electrons, respectively. Careful though…"resonance" applies to a particular kind of interaction, not a particular kind of particle. Ultraviolet-visible spectroscopy is another kind that analyzes resonance of electrons, but it's not related to EPR. DMacks —Preceding signed but undated comment was added at 18:52, 14 October 2007 (UTC)

exlcuding nmr - all these resonances are at frequencies above that of visible light - the difference between 'resonance' frequencies of electrons is electronic spectroscopy (the term resonance is possible debateable here - depending on what theory you have), the differences between energy states in nuclei is in the x-ray or gamma ray region - again it's debateable whether or not the nuclei are actaully resonating - and depends on what theory you are using..

Note that electronic spectoscopy (the electrons) also depends on the type of molecule the electrons are in - there's also (for lower down electrons) mossbauer spectroscopy and X-ray photoelectron spectroscopy amongst others,not all these spectrosopy are interpreted as being directly from resonances..87.102.82.26 20:50, 14 October 2007 (UTC)

And you can get crazy and do Raman spectroscopy, which is a measurement of electronic transitions that indicates bond vibrations. This is similar to using IR, which only examines vibrational modes, to see the effect of rotational modes on those vibrations, instead of using Microwave spectroscopy to probe rotational modes more directly. DMacks 22:10, 14 October 2007 (UTC)

CLASSIFICATION

What would a scientist have to prove to show that the organisim they had discovered was a new species?

What would you expect to see in the organisms within groups that get smaller and smaller. 88.110.21.169 18:38, 14 October 2007 (UTC) Alex McAdam

I suggest checking out the Species and Species problem articles. As for the organisms in groups that get smaller and smaller -- fortunately, there are a finite number of organisms on Earth, so if you kept dividing organisms into group, you'd at least hit the limit once you created a new group for each organism. -- JSBillings 18:59, 14 October 2007 (UTC)

Usually a lack of cross breeding with other similar species of organisms is what you need to prove that an organism is a new species. How exactly this is determined may vary between different organisms. 71.226.56.79 22:13, 14 October 2007 (UTC)

I posted this in a question below but it seems to be important to this one as well. Sometimes the line between species are drawn for reasons other than "can two species interbreed". Even if two organisms can interbreed they may still be considered separate species based on the fact they wouldn't likely interbreed in the wild because they are separated geographically, or because their behaviors are suitably different, etc... See the hybrid page for some examples. Taxonomy has all manner of inconsistencies and politicking. A cross between a Bullock's Oriole and a Baltimore Oriole produces fertile offspring, but the two may be considered separate species or the same species called the Northern Oriole depending on who you talk to. Animal taxonomy is arguably the most straight forward. Plants are probably next but can be a nightmare taxonomically because many "species" can cross rampantly. Fungal taxonomy is all over the place and still developing. Many fungal species have multiple nomenclature synonyms simply because the various reproductive stages of fungi appeared different only to be found to be the same thing later. I don't know enough about protista and bacteria, but I can guess they probably can get rather messy as well. Sifaka ^talk 02:13, 15 October 2007 (UTC)

Absolute zero

I just want some input on my reasoning about this topic, or any other speculations that are floating around out there.

Absolute zero is the lack of all energy, right? So if you managed to get an atom down to absolute zero, what would happen to it? Don't electrons have potential energy based on their orbital position? In order to reach absolute zero, would they have to fall into the nucleus? What would happen then?

For curiosity's sake... justice 18:41, 14 October 2007 (UTC)

Thermodynamicists say it isn't possible to reach absolute zero. Xn4 18:48, 14 October 2007 (UTC)

Our absolute zero page has info about this topic. One important issue is that "Absolute zero is the lack of all energy" is a convenient and short explanation for the general public, but it's not the precise and correct definition. As you note, there is a non-zero minimum for various potential energy components. DMacks 18:49, 14 October 2007 (UTC)

Theoretically though, for you to reach absolute zero the electrons couldn't stay in their orbitals because of potential energy. If they hit the nucleus, what would happen? Also, I'm assuming that in real life, if we can never reach absolute zero, it's an like an exponential function- always getting closer to whatever number, but never quite reaching it? justice 19:08, 14 October 2007 (UTC)

Again, I point you to the absolute zero page, which states "It is the point at which particles have a minimum energy, determined by quantum mechanical effects, which is called the zero-point energy.". They don't stop moving and they don't have zero potential energy. DMacks 19:12, 14 October 2007 (UTC)

Yes, a necessary result of quantum mechanics is that you can never get rid of zero-point energy. Someguy1221 19:19, 14 October 2007 (UTC)

There is a certain elegant symmetry here - Einstein says we can't reach infinite kinetic energy - and the third law of thermodynamics says that we can't reach zero kinetic energy either. Nature seems to love having exponential tails to avoid having mathematical discontinuities. SteveBaker 21:31, 14 October 2007 (UTC)

The third law applies to statistical ensembles of particles. Individual particles within an ensemble may well obtain a state of minimum possible kinetic energy, such as happens to the majority of particles in a Bose-Einstein condensate. Dragons flight 23:15, 14 October 2007 (UTC)

It's also worth noting that ending up with zero energy could have weird implications for what it means for fundamental particles to "exist". What happens to light if it has no energy? Light is defined (in part) by its wave-like properties — would it even make sense to talk about it as existing if it had no energy, no motion? I'm no physicist but I imagine similar issues come up when you are talking about matter as well, given the deep connection between energy and matter. --24.147.86.187 22:25, 14 October 2007 (UTC)

I was going to ask about that. So nothing, as best we understand it, would exist without energy? If it had no energy, the matter would be... destroyed? justice 22:55, 14 October 2007 (UTC)

No, no, no! Not "Zero Energy" - we're talking about temperature - which is "Kinetic Energy" - mass times velocity squared. When the velocity of an atom drops to zero (so you get absolute zero temperature), it still has mass - so it still has energy of the E=m.c² variety - it's just kinetic energy that hit zero because that's mass multiplied by velocity and when velocity is zero, the kinetic energy is zero no matter what the mass is. I agree with User:Dragons flight too - single atoms can have zero kinetic energy. SteveBaker 15:06, 15 October 2007 (UTC)

question on Sexually transmitted disease--why aren't there more of them?

Why there are apparently relatively few STDs? I think there "ought" to be hundreds of well known STDs. I mean, fluid exchange during sex is a jackpot for microcritters to evolve to take advantage of. Could it be that these missing STDs are really there but are wrongly presumed to be genetically heritable diseases, defects,(or even advantageous traits!?) since they would commonly run in families?-Rich Peterson —Preceding unsigned comment added by 130.86.14.86 (talk) 20:53, 30 September 2007 (UTC) (I put this on the STD discussion page a while back, but that isn't the right place for it, according to Wikipedia policy)130.86.14.90 20:02, 14 October 2007 (UTC)

You're running on some pretty strong assumptions there. Genetic defects are not diseases, as they are... well, not diseases. They're flaws in the DNA that cause abnormal conditions in the body's development, not body parts being attacked by a specific organism. Second, why should there be "hundreds of well known STDs." Sexual fluids are actually a less efficient method of spreading disease than blood or airborne transmission. There's nothing inherently special about sexual fluids that should be a "jackpot" for diseases. -- Kesh 20:09, 14 October 2007 (UTC)

I know what a genetic defect is.What I'm proposing is that some things thought to be genetic defects are actually diseases transmitted semen.I am interested in what you say about sexual fluids not being as efficient, perhaps you're right. Can you explain your reasoning or refer me to a source? Thanks, Rich Peterson—Preceding unsigned comment added by 130.86.14.90 (talk • contribs) 22:56, October 14, 2007

Please read disease. A disease is a foreign organism that enters the body and damages it in some way. Genetic defects are inherent in the DNA of the child. How are you proposing that a disease could A) stick around in the mother's body long enough to infect the fetus, yet B) be undetected in the mother OR the fetus, C) not harm the mother and D) continue to affect the child throughout its development? -- Kesh 23:03, 14 October 2007 (UTC)

I think you may be inadvertently defining a possibility out of existence, by use of the word "disease". In answer to A and B and C, it's not too different to what most parasites struggle and adapt to do over time, though some may not be hidden but are perceived to be genetic defects, rather than stowaways in fluids for gene transmission. Thanks for your comments.--Rich Peterson

At this point, I'm not even sure what you're proposing. The causes of genetic defects are in the DNA of the child, inherited from the parent. An STD is a disease, a microorganism. The two are not even similar. The mechanics behind both are rather well understood, so I don't see how a disease can "masquerade" as an inherited defect. -- Kesh 23:35, 14 October 2007 (UTC)

I agree with part of what you say if you mean a disease's strategy is to 'masquerade" as a genetic defect--that surely wouldn't happen as often. I mean perceived by us in our ignorance, not an intentional masquerade. What "is rather well understood" may or not be just a portion which is "rather well understood." For example, there is no telling for sure that the the two that "are not even similar" don't have a large, and unknown, range of intermediates.--Thanks, thats's all for today for me.-Rich Peterson —Preceding unsigned comment added by 130.86.14.90 (talk) 00:13, 15 October 2007 (UTC)

At that point though, you're venturing into philosophy territory. That there may be things we do not know is obvious. However, going from that to saying "diseases are causing these defects" is a huge leap of faith. There's nothing whatsoever to support it in science. -- Kesh 00:19, 15 October 2007 (UTC)

I don't think sex is a good way for a disease to transmit itself at all. Humans are relatively monogamous and typically have sex just a few times a week - mostly with the same partner. A common cold virus is transmitted between complete strangers via nothing more than a handshake, a cough or a sneeze - with an opportunity to transmit itself dozens and dozens of times per day. SteveBaker 21:27, 14 October 2007 (UTC)

Careful Steve, humans are not that monogamous. If you've ever had a partner who has had at least one other partner, you are part of the great sexual network. I do agree though, airborne is the best way for a pathogen to go. Returning to the original question, STDs aren't super easy to pass to your kids (it depends on the STD of course, but AIDs for example, is preventable to about a 15%-25% transmission rate in the West), and mistaking them for genetic defects seems pretty far fetched. Also, remember that diseases "should" evolve to become less noticeable and less virulent, so there are probably "STDs" that we don't even classify as diseases anymore. --Cody Pope 21:39, 14 October 2007 (UTC)

--I think "so there are probably ""STDs" that we don't even classify as diseases anymore" supports my proposal. I did suggest an STD could even be advantageous as an extreme case of what, as you say, tends to happen-diseases evolve to become less noticeable and less virulent. Thanks for your comments.--Rich Peterson

Sheesh! I said "relatively monogamous" and "typically" - just how careful do I have to be? The point is that it's pretty much impossible to have sex with someone without passing on a cold. So it's pretty much certain that a disease that can transmit itself through the air is going to have more potential contacts to spread to than an STD. The spread of AIDS is pathetically slow compared to whichever cold or flu strain is unleashed in a given year. Even in the countries where AIDS has spread the furthest, you're only looking at 10 to 20% of the population over 20 or more years. A strong flu strain can spread to a similar percentage of the population in a couple of months. SteveBaker 22:07, 14 October 2007 (UTC)

Hey, I attacked "relatively" not "typically" -- man you do need to be more careful :). But mostly I completely agree with you. --Cody Pope 22:22, 14 October 2007 (UTC)

Compare that to how often you've breathed the same air as someone. I'm not certain, but I'd be willing to bet that most people also share drinks more often then they have sex. In addition, I'm pretty certain that almost all diseases can be transmitted that way, and STDs are the ones that can only be transmitted blood to blood. — Daniel 22:00, 14 October 2007 (UTC)

Hmm, I was agreeing with Steve's observation that airborne is way more common/easy, but disagreeing with him saying that we're all monogamous -- so I'm not sure how we disagreed. Plus, I really just wanted to say "great sexual network" :). Moreover, "almost all diseases can be transmitted that way" is an odd statement (where "that way"=airborne?). Ebola is transmitted through fluid exchange (non-sexual and sexual alike) and it's certainly not classified as an STD. A lot of parasites need a vehicle that isn't air. As well as malaria, non-parasitic dysentery, TB (airborne momentarily, sure but only if someone just sneezed in your face, the bacteria isn't transmissible through sharing water glasses washed dishes though) and others. Take African sleeping sickness, it is usually passed by a fly, but can theotrically be passed via fluid exchange etc. Saying anything transmitted via fluid exchange is an STD doesn't work. --Cody Pope 22:13, 14 October 2007 (UTC) (I would add that people with Ebola almost never have sex). --Cody Pope 22:25, 14 October 2007 (UTC)

I just don't see your point about efficiency or effectiveness of transmission. First, there's quite a lot of different germs that transmit by air etc, far more than the few hundred for sexual transmission I'm proposing. Second, even if very few germs were transmitted by semen, say a few eons ago, there would be lots of time for them to speciate--some adapting to become less virulent, and every once in a while a few "choosing" the greater virulence strategy.-Regards and thanks to all for your thoughtful comments.--Rich Peterson

The point is that it's simply not as effective a method of transmission. Speciation tends to favor the best methods of continuing the species which, for diseases, means they tend to favor the more reliable/easier methods of spreading. Thus, more airborne diseases than fluid-borne ones. -- Kesh 23:44, 14 October 2007 (UTC)

Yes, but I don't mean to suggest there should be more fluid-borne than airborne diseases, I don't know. I only suggest there are MANY fluid-borne ones, more than we suspect. Also, a species transmitted by a fluid would be reasonably likely to have at least some of its daughter species use the fluid route.--Rich Peterson —Preceding unsigned comment added by 130.86.14.90 (talk) 00:00, 15 October 2007 (UTC)

You've still not explained why there should be more than we are currently aware of. -- Kesh 00:03, 15 October 2007 (UTC)

Ok, to summarize, if I understand the conversation so far, Rich argues that there should be more STDs since sex is a good vehicle for transmission and others are saying that sure sex is a great mode, but airborne is way better (where "better" means faster). Now, Rich also argues that it is possible that we have misidentified STDs as Genetic defects, since they could be passed to children by parents and might only present in development. Is that about it? First, airborne is faster and thus ideal for anything that wants to reproduce quickly. Second, sure, I agree that it is possible for us to misidentify a disease as a defect under the conditions that: a. it can be passed from mother to child, b. it is unknown to science, and c. it causes some developmental problem. But, I also contend that given the level of modern medicine this is highly unlikely, since, "a." only happens about 15-25% of the time (for HIV at least), "b." is untestable, and "c." is probably not happening given that many if not most developmental problems have identifiable causes. Tangentially, my problem with the question is more about the limited definition of "STD". Take a look at HPV for example: "of about 13 so-called 'high-risk' sexually transmitted HPVs". There are over 100 HPV forms, and only about 13 are considered STDs. Now all of them can be transmitted by sex (skin contact really). The common cold can be transmitted by sex (kissing and coital fluid exchange). Ebola can be transmitted by sex (any fluid exchange really, touching soars etc). So our working definition of STDs doesn't seem super effective when you're discussing the evolution of diseases and their radiation. We could simple say that Rich's "lost" STDs are all those virus/pathogens/bacteria that can be transmitted via sex but are most often not (or at least not associated with sex in the traditional sense). So to summarize: fluid exchange is not the jackpot it could be, since it is slow. STDs being misidentified as genetic defects is possible but improbable. And if you just change the definition of STD you get a whole bunch of speciation in your new group. --Cody Pope 04:30, 15 October 2007 (UTC)

On HPVs, actually only 13 are "high-risk STDs", that doesn't mean that none of the others are STDs. The article says, "A group of about 30-40 HPVs is typically transmitted through sexual contact", thus about 30-40% are STDs. A "high-risk STD" is one that includes a risk of death, as noted in the Cancer section that says, "About a dozen HPV types [...] are called 'high-risk' types because they can lead to [various forms of cancer]." The section on HPV caused genital warts (which is an STD) notes that they are not "high risk" because they don't cause cancer. The reason why so few are "high-risk" is not because STDs are hard to contract, but because they increase the odds of killing off the host, which is a maladaptive trait compared to the more benign versions of HPVs. -- HiEv 17:41, 15 October 2007 (UTC)

Actually, this is a pretty good question. To start off with, there are already quite a few STDs, with over 100 species of Human papillomavirus (HPV) identified so far alone. Besides that, the fact is that there are probably many more STDs that we're not aware of, but they're not noticed due to being fairly benign. If a bacteria or virus is transmitted, but there are no symptoms, then people aren't likely to look for it or try to figure out how it was transmitted.
Also, there are diseases that seem to run in families, so we assume that there is a genetic component to the disease, however this could be in error. Researchers are still searching for genes responsible for some apparently genetic diseases. However, what appears to be a genetic condition might actually be due to an environmental cause, such as exposure to a certain germ. If a virus, for example, had evolved to be able to infect a foetus in the womb then it might cause some early developmental changes that affect later growth. For example, while often thought to be genetic, some suspect that one of the causes of schizophrenia could be due to prenatal exposure to infection by the parasitic protozoa Toxoplasma gondii.
Still, there are many problems with this, such as the difficulty in infecting the foetus (as seen above in the AIDS numbers) without killing it, the long dormancy period that would be required from birth to sexual maturity, the fact that negatively affecting the future host reduces its ability to spread, the length of time it would take to evolve to be able to cause a positive adaptation in its future host, and an explanation as to why it would stick to some families and not spread more randomly among the population as other STDs do.
So, yes, there probably are more STDs, but for the most part it's unlikely they're ones worth worrying about, and it's very unlikely, though not impossible, that they're the cause of any apparently heritable conditions. It sounds like it might be worth investigating scientifically, but currently I wouldn't put the odds in favor of it being true. -- HiEv 17:18, 15 October 2007 (UTC)

• It depends how you are defining STD. Is an STD something that is only transmissible by sex (or a sex-like act such as a blood transfusion), or is an STD something that is transmissible by many means, including by sex? By the latter definition, almost every disease is an STD. You can catch flu by having sex with someone -- it's just that you could just as easily have kept your pants on and caught it. --M@rēino 21:02, 17 October 2007 (UTC)

I'd say an STD is something that is primarily transmitted due to sexual contact. After all, there are ways to get any transmissible disease without sex. For example, you can get AIDS from a blood transfusion. So if you say an STD is a disease only transmissible by sex then there are no STDs. -- HiEv 14:06, 18 October 2007 (UTC)

Mitochondrial genome size

Everyone seems to know that the mitochondrial DNA in humans is 16569bp long. This comes from a 1981 paper that sequenced it. My question is: there's gotta be some variation in this number - does anyone know how much give and take there is in humans? Aaadddaaammm 22:19, 14 October 2007 (UTC)

Here is a place to start: Mitochondrial diversity within modern human populations. --JWSchmidt 22:27, 14 October 2007 (UTC)

I didn't know the size of the mitochondrial genome if it makes you feel better. :P I am positive it would vary as is it subject to the same (or more as mitochondrial DNA copying machinery is slightly less fullproof than nuclear DNA copying machinery) random duplication and deletion events as the nuclear DNA. That number is probably good for an average. Sifaka ^talk 02:17, 15 October 2007 (UTC)

species

Does the inability of one species to impregnate another species serve as the dividing line for species or does it include the ability to impregnate but with the result of offspring so deformed they are not able to live? Clem 22:32, 14 October 2007 (UTC)

Neither. For instance, horses and donkeys can interbreed, but create infertile mules. They are still considered separate species, as their offspring cannot breed, even though said offspring are not deformed. Most modern biologists look at more than that, though, as genetics and bodily structure play into the definition of species quite a bit. It's not as simple as who they can breed with. -- Kesh 22:35, 14 October 2007 (UTC)

Generally, both genders of any offspring between the two have to be themselves fertile. Mules aren't. Of ligers and tigons, only the females are. Not sure about grolars, but then they're a lot rarer. GeeJo ^(t)⁄_(c) • 22:42, 14 October 2007 (UTC)

I don't know about grizzly bears in particular but as Ursid hybrid mentions, some brown bears are more related to polar bears then they are each other which is something I've also read before in scientific papers. It also appears to suggest that both sexes are fertile which isn't surprising although not guaranteed by the DNA studies (polar bears could have some specific difference other then their colour which prevents them successfully interbreeding) Nil Einne 11:52, 15 October 2007 (UTC)

Sometimes the line between species are drawn for reasons other than "can two species interbreed". Even if two organisms can interbreed they may still be considered separate species based on the fact they wouldn't likely interbreed in the wild because they are separated geographically, or because their behaviors are suitably different, etc... See the hybrid page for some examples. Taxonomy has all manner of inconsistencies and politicking. A cross between a Bullock's Oriole and a Baltimore Oriole produces fertile offspring, but the two may be considered separate species or the same species called the Northern Oriole depending on who you talk to. Animal taxonomy is arguably the most straight forward. Plants are probably next but can be a nightmare taxonomically because many "species" can cross rampantly. Fungal taxonomy is all over the place and still developing. Many fungal species have multiple nomenclature synonyms simply because the various reproductive stages of fungi appeared different only to be found to be the same thing later. I don't know enough about protista and bacteria, but I can guess they probably can get rather messy as well. Sifaka ^talk 01:54, 15 October 2007 (UTC)

JSBillings suggested checking out the various concepts of species and Species problem articles in a similar question above. Sifaka ^talk 01:56, 15 October 2007 (UTC)

Yeah - you can cross a Lion with a Tiger and get a Tigon or a Liger (yes, really!) - but nobody would consider Lions and Tigers to be the same species - we "know" they are different because they look different, they behave totally differently (tigers are lone hunters, lions are pack animals, tigers love to swim, lions don't), they sound quite different (lion roars and tiger roars sound way different) - you can easily tell the difference between a male and female lion by the mane - no such clear difference exists with tigers...stripes...you name it. For sure we don't want to call lions and tigers by the same name. On the other hand, we do want to call all dogs "Dogs" - even though they look/behave/sound more different than lions and tigers do, they actually are closer genetically than lions and tigers.

The problem is that we have this big pile of taxonomic data with lots and lots of history to it - and we're loath to toss it all out, even though it's evident that the whole thing is a big blurry mess of genetics. The inability to interbreed could be due to just one teeny-tiny genetic incompatibility - or it could be that there are thousands of genetic differences that none-the-less do not prevent interbreeding. Then we have the 'mule' situation where the offspring of two different kinds of animal is infertile, or the situation with tigons and ligars where the female offspring are fertile, but the males are not, or the situation with Great Danes and Shi-Tsu dogs where the offspring are all fertile but will probably have weird health problems of other kinds. Using that 'interbreeding' criteria as a way to name things is an old, outdated idea.

But to come up with an entire new taxonomy based on genetic differences measured directly by number of different genes would require huge amounts of effort, thousands of textbooks been rewritten, endless wrangling over who gets to name what 'new' species with what name and which name to call the result of two sub-species being grouped together. This is a horrible mess - but in the end, it really doesn't matter all that much...it's just a matter of terminology.

SteveBaker 14:20, 15 October 2007 (UTC)

• I bet taxonomists could play a fun six degrees of Kevin Bacon sort of game where you try to link two distant species by breedable species in between, in the style of a ring species. I wonder what the longest such chain among extant creatures is? --Sean 15:26, 15 October 2007 (UTC)