Wikipedia:Reference desk/Archives/Science/2012 December 5

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December 5

Subjective time

When hiking for four miles in and four miles out in a relatively unfamiliar area, my perception is that a landmark which I remember from "about halfway" on the way in is at little more than 1 mile in on the map; thus invariably when hiking I find that most of the landmarks I've remembered come out in rapid succession "close to" the end of the return trip. I take this to support an idea that subjective time, whether on a short or lifetime scale, depends on novelty (or retroactively from memory?) and runs according to the 1.7 or 1.8th root of clock time (it is relatively easy to derive a square root relation mathematically). Is there any literature on a subjective time formula that is more believable than the IMHO absurd inverse proportion mentioned in the article? Wnt (talk) 01:26, 5 December 2012 (UTC)

Instead of highway hypnosis...hiking hypnosis.GeeBIGS (talk) 02:43, 5 December 2012 (UTC)

I suspect that it's not a fixed formula, but depends on what you encounter on the way. In general, the things you encounter on the first half of a trip will be "newer", so you will notice them more (like the 1st weeping willow tree, perhaps), but notice subsequent appearances of similar objects less. So, it will seem like you encountered more during the first part of the trip than the last. However, if the first half was boring and then you hit some fantastic scenery, that might alter your perception. StuRat (talk) 06:25, 5 December 2012 (UTC)

The memorability of landmarks certainly depends on their novelty which decreases as one penetrates further into the previously unknown area. Since this observation depends so heavily on unpredictable subjective factors and previous experiences, it seems impractical to derive a meaningful mathematical relation to time (or distance) passed. SkylonS (talk) 11:22, 5 December 2012 (UTC)

I have always noticed that the first trip to a new destination always takes longer than the return and the second trip there even less time than that, tending to a constant rate on about the third and later trips. Is this (at least similar to) what you are talking about? μηδείς (talk) 16:46, 5 December 2012 (UTC)

Not really. In this instance worry about deer season had pushed me to a simple, straight path, which I'd already checked on the map before going, along the bottom of a valley with regular distance markers. I didn't even need to note landmarks, and my rate of travel was very nearly constant. Even so, I paid more attention to the distance markings on the way back, and was "predictably surprised" to find the thing I'd thought of as being halfway out not far from the first mile marker. Wnt (talk) 20:48, 5 December 2012 (UTC)

Buttons

Are all silver metal buttons on pants nickel?--Wrk678 (talk) 06:07, 5 December 2012 (UTC)

I doubt it. Some might be painted silver, with steel or some other metal underneath. Some might be copper or nickel-plated. And, for expensive high-fashion clothes, they may actually use silver (solid or plating). There may not be any which are all nickel. StuRat (talk) 06:21, 5 December 2012 (UTC)

I'm wondering because I'm allergic to nickel. Is it usually nickel plated. They are just 30 dollar pants. — Preceding unsigned comment added by Wrk678 (talk • contribs) 06:47, 5 December 2012 (UTC)

I've seen pants with plastic and cloth-covered buttons, but the zipper and any rivets might be a problem. You can get pants without rivets, but the zipper might be a problem. I've seen plastic zippers on coats, but not pants, since they need to be larger. There are button-fly jeans, but I don't know if you can get those in nickel-free buttons. Velcro would be ideal. Have you considered having pants custom made ? StuRat (talk) 07:37, 5 December 2012 (UTC)

Here's a site which sells nickel-free buttons and rivets, so you can have a tailor replace the ones on your pants: [1]. No mention of the zippers, though. They also have a test kit, so you don't have to trust the salesman who claims their pants are nickel-free: [2]. StuRat (talk) 07:42, 5 December 2012 (UTC)

I'm just wondering if most silver metal buttons are nickel plated.--Wrk678 (talk) 08:54, 5 December 2012 (UTC)

Well on [3] I see about one in six of the jeans metal buttons tested contained nickel. You might get away with just coating them with clear nail enamel just in case. Dmcq (talk) 09:45, 5 December 2012 (UTC)

Could you just paint the buttons with something like clear nailpolish? Vespine (talk) 21:33, 5 December 2012 (UTC)

Light traveling to a star

As I understand it, while the universe is 13.7 billion years old, the actual current distance from here to any star (let's talk about red dwarfs, which last a long, long time) that we've ever seen is more like 45 billion lightyears, due to expansion of the universe that has occurred since the light we see was emitted. As I also understand it, there could be some stars that we cannot see because their light could never reach us, and that are unreachable by light that we send out.(Correct me if I've got these things confused.)

Suppose there's a visible star that's x lightyears from us in terms of when it emitted the light that we currently see. Based on what we know now about the past and future history of expansion of the universe, are there stars that we currently see that we could never reach with a beam of light? If so, what is the critical value of visible distance x above which the star is unreachable by light that we currently send? Duoduoduo (talk) 15:55, 5 December 2012 (UTC)

Given that it's impossible for a star to move at the speed of light, if we sent a beam of light to x star, at some point in the future (billions of years perhaps) the light would reach that star (assuming it isn't swallowed up by black hole or distorted in some other way). I've got no idea of the rate the universe is expanding at, but again, assuming that it's less than the speed of light - a beam of light would, in theory, eventually reach the most distant part of the universe. Conversely, if the universe is expanding at the speed of light, then it wouldn't as light cannot travel faster than the speed of light. I may have got that completely wrong, I'm no expert at physics this advanced, so if I have, any astro-boffs feel free to correct me. douts (talk) 16:45, 5 December 2012 (UTC)

I thought it's established that there are stars that cannot communicate with us, and I thought that that was due to the expansion rate of the universe being greater than the speed of light. If so, my question stands. Or is it known that the expansion rate was only greater than the speed of light during the inflationary period, and not now, and never again? I can't tell from the article Metric expansion of space. Moreover, even if a star is moving away from us within space at of course less than light speed, and even if the universe itself is expanding at less than light speed, couldn't the sum of those two exceed the speed of light, making the star unreachable by our emitted light? Duoduoduo (talk) 17:03, 5 December 2012 (UTC)

I dont know is the honest answer, I'm not clued up enough on astrophysics to be able to give you a good answer. My response above is based my very limited physics knowledge. I'm sure there are other users who are much more clued up on this than I am. Sorry I couldn't be of more help. douts (talk) 17:23, 5 December 2012 (UTC)

They think the expansion rate was greater than the speed of light at some time in the past, but is not now. thx1138 (talk) 17:40, 5 December 2012 (UTC)

No, the expansion was never faster than light (that's a common misconception). More precisely, the rate of the expansion doesn't have units of speed, so it can't be compared to the speed of light. (The units are time⁻¹, often given as kilometers per second per megaparsec.) -- BenRG (talk) 22:16, 6 December 2012 (UTC)

... but the expansion is speeding up at present, and we can currently observe galaxies with a red-shift greater than 1.5 which we believe are currently "receding" from us at a separation speed greater than the speed of light. (Please note that this doesn't mean that these galaxies are "travelling" faster than light.) Also galaxies at an estimated current distance of about 4,740 megaparsecs (146 million million million million miles) will soon disappear forever from our view because their light will never reach us. Galaxies further away than this (assuming that they exist) can never be observed by us (unless we find "wormholes" or some such trick to move without travelling). I don't have a figure for your "x" distance for light to reach the star from us, but I'm sure there are some experts here who can calculate it. Dbfirs 18:20, 5 December 2012 (UTC)

Galaxies do not disappear from our view. Ruslik_Zero 18:41, 5 December 2012 (UTC)

What makes you think that? The article Future of an expanding universe claims that in another two million million years all galaxies will have become undetectable except for those in our local cluster. Dbfirs 23:56, 5 December 2012 (UTC)

Technically they are still "in our view" but they are redshifted to the point of invisibility. It's the same as a black hole event horizon: you see a finite part of the galaxy's future redshifted over an infinite time. -- BenRG (talk) 22:16, 6 December 2012 (UTC)

• See observable universe, which discusses these issues. It says some galaxies exist which we can see at early development, greatly redshifted, but light from them from later times will never reach here. How many can we see in their present form? Well, none, of course (unless you use a speed of light frame of reference...) Wnt (talk) 20:56, 5 December 2012 (UTC)

Thanks for the link. Like most people, I struggle to get my brain round the complexities the current understanding of the universe, but I think the answer to the OP's "x" is 16 million thousand million light years (corrected) (94 thousand million million million miles) as measured now. No doubt someone will correct me if I have misunderstood the symmetry. I'm not a cosmologist! Dbfirs 23:56, 5 December 2012 (UTC)

It's 16 billion (= thousand million, not million million) light years if ΛCDM is correct. ΛCDM is the simplest model that fits the data so far, but it could easily turn out to be wrong. In general the distance is $\int _{\mathrm {now} }^{\infty }{\frac {c}{a(t)}}dt$, where a(t) is the scale factor of the universe. Since this distance depends on the scale factor at all future times, the number you get is quite sensitive to the model. If the cosmological constant ever decays to zero, the integral becomes infinite (meaning any distance is conceivably reachable). -- BenRG (talk) 22:16, 6 December 2012 (UTC)

Thanks, Ben, and apologies for the error (corrected above). I was hoping you would contribute because I'm unsure of the complexities (and, from what you say, cosmologists are unsure of their models). Is it still possible that the universe is finite and that some of the "distant" observed galaxies are really just nearer ones with the light having travelled right round, or has that possibility been ruled out by some recent evidence? ... (later) ... I think Shape of the Universe has the answer to my question if it's up to date. Dbfirs 10:46, 7 December 2012 (UTC)

It looks like any wrapping around at a scale substantially smaller than the size of the visible universe is ruled out by searches like this (which should be in the shape-of-the-universe article). The universe could wrap around at a larger scale and we'd never know. -- BenRG (talk) 03:16, 10 December 2012 (UTC)

Variable displacement with open exhaust valves

According to variable displacement, when a cylinder is deactivated all of its valves are closed. The piston then continuously work against the trapped exhaust gases infinitely until that cylinder is reactivated again. Is there any engine out there that keep the exhaust valve open continuously during deactivation? It seems by keeping the exhaust valve open less work will be wasted.Dncsky (talk) 16:25, 5 December 2012 (UTC)

I think I see a problem with that. You would then be pumping exhaust air (from the operational cylinders) in and out of the cylinder, and I bet that would cause deposits to accumulate in the cylinder in question. StuRat (talk) 17:05, 5 December 2012 (UTC)

Doh! How did I not see that before. Thanks for your help.Dncsky (talk) 17:07, 5 December 2012 (UTC)

Resolved

Besides, the work done on the gas trapped in a contained cylinder is conservative (parasitic losses ignored). In this case, the parasitic losses would be... gas escaping by leaking out. So, opening the valve actually is detrimental, as it makes the engine more lossy and less efficient. By keeping the system closed, any energy spent by the engine during compression is recouped in the next phase of the cycle. The problem is then reduced to an engineering technicality, the objective being to smooth out the power variations over a cycle. Nimur (talk) 17:10, 5 December 2012 (UTC)

The heat of compression would be transferred from the gas to the cylinder walls and to the radiator. If the exhaust valves were open there would be no compression and thus no heat loss due to compression.Dncsky (talk) 17:16, 5 December 2012 (UTC)

If the cylinder is perfectly closed, upon decompression the exact same amount of heat would go right back from the cylinder walls and into the gas inside the cylinder. Now, as I said above, we have an engineering practicality to consider: which parasitic loss is worse - the energy lost to turbulent convective air movement, or the energy lost to thermal conduction to the outside world? It seems that the engineers who design engines have carefully considered the problem, and decided to use a closed cylinder. That would seem to indicate that wicking away of thermal energy by the engine block is a less lossy process than turbulent airflow, which makes intuitive sense to me. In your own engine, with its own size, shape, and material properties, your mileage may vary, literally and figuratively. Nimur (talk) 18:10, 5 December 2012 (UTC)

Under full load conditions, the amount of heat lost through the cylinder walls to the coolant, and through the piston into the oil, is of the order 6% of the total combustion heat. Note that the total heat rejected to coolant is much much higher than this, as it includes heat lost in the cylinder head exhaust passages and exhaust valve (around 15% typically) and losses due to piston ring and bearing friction (which ends up as heat in the coolant). See R F Taylor's or Harry Ricardo's classic textbooks on high compression engines for typical figures. The 15% loss in the head will not happen if the exhaust valve does not open. 6% is a low value to start with. However, if the cylinder is not firing, the gas temperature will only be a small fraction of the combustion temperature, lowering the heat conducted to the cylinder wall and piston. Further, this heat flow is aided by gas turbulence within the cylinder. Some turbulence is driven by the shape of the piston top, but a lot is driven by the the gas flow past the intake valve. If the intake valve does not open, turbulence will be less, lowering the heat loss still further. My rough estimate (to complex to set out here) is that when not firing, the cylinder heat loss to coolant will drop to less than 8% of the full throttle value, which was only 6% of combustion heat anyway. Keit 120.145.164.75 (talk) 01:04, 6 December 2012 (UTC)

Using the numbers you provided the other day:

Brake Power Output:........265 kW (39%)

Total Loss to Coolant:....164 kW (24%)

Loss to exhaust:..............233 kW (34%)

Loss from engine surfaces..19 kW ( 3%)

Loss from closed valve variable displacement: 683kW * 6% * 8% = 3.3kW

3.3kW is admittedly negligible, but it's still larger than if the exhaust valves were open. But like Sturat mentioned opening the exhaust valves is unfeasible. Dncsky (talk) 01:50, 6 December 2012 (UTC)

I think you are right - loss with valves open should be less. StuRat was concerned about deposits, but I not sure this is a real concern. The Caterpillar 3516 engine (diesel, 2500 kW max output) with electrically controlled fuel injection turns off cylinders at low speeds and loads (unless this feature is disabled at customer option) by not pulsing the injectors in selected cylinders. The intake and exhaust valves continue to operate normally. Soot will not build up in the "off" cylinders as they are still pumping air through. It also picks different cylinders to turn off each time it decides to do it. In a gasoline engine, soot should not be forming. StuRat also realised that there would be new pumping losses in and out the cylinder. It is hard to accept that these would exceed the loss with valves closed, as you can view it as reducing compression, thus reducing the conversion of mechanical effort into heat to be conducted away. Keit 120.145.164.75 (talk) 03:03, 6 December 2012 (UTC)

But.... if the heat of compression is conducted away, then won't the loss of heat from expansion be refilled from conducting heat in? Gzuckier (talk) 02:00, 6 December 2012 (UTC)

Some of the heat will be conducted back to the gas, some of it won't. The part that doesn't goes into the coolant and then outside the car. Dncsky (talk) 02:45, 6 December 2012 (UTC)

Heat conducted into the gas during the low pressure part of the compression-expansion cycle will be less than the heat conducted out of the gas during the high pressure part of the cycle, with the geometric mean gas temperature equal that of the cylinder walls. This will modulate the piston pressure resulting in a net mechanical loss. Keit 120.145.164.75 (talk) 03:08, 6 December 2012 (UTC)

Here's another thought on this. Sorry, I know of no references to refuse or support it. Many people think that the exhaust gasses are driven out of the cylinder throughout the exhaust stoke (approx 180^O crank rotation), but this isn't so. What actually happens is a blowdown phase when the valve opens, followed by a relative calm equalisation phase. The blowdown phase typiclly lasts 5 to 15 degrees of crank rotation, and during it the bulk of the exhaust gasses leave at a veclocity equal to the speed of sound (that's what makes the whack whack whack noise if there's no muffler). A lot of heat is transfered to the exhaust valve due to the presure and velocity. But during the remaining 700 degrees or so of crank rotation in the 4-stroke cycle, the valve can loose its heat via the valve stem into the guide, and for approx 540 degrees it is in contact with the valve seat. Even so, exhaust valves run hot, red hot.

If the exhaust valve is held open on a non-firing cylinder, with the intake valve closed, hot exhaust gases will be pumped past it thoughout the complete cycle. The gasses won't be a full exhaust temperature, as some cooling between cylinders will occur, but as it is continuous on the dead cylinder valve, and not a mere 10 degrees or whatever, it could mean the valve will run hotter than during firing, and could be past its' limit.

This is not a problem with diesel engines (eg Cat 3516) because cylinders can be shut down by ceasing fuel injection - the valves operating normally and pumping air through. But you can't do that on a conventional gasoline engine as the fuel is mixed with the air before the intake valves, so fuel would be wasted. But if you had a separate throttle body and fuel system for each cylinder???

Ratbone 121.215.53.208 (talk) 04:07, 6 December 2012 (UTC)

Antidepressants

How can pharma. cos. and the dr. and scientists they employ to test these drugs be so sure that they "may cause suicidal ideation", yet not also cause homicidal ideation? Logically, presuming that "this may caues you to care less than you currently do about your own life" it would follow that it might also "cause you to care less than you currently do about a random stranger's life"165.212.189.187 (talk) 18:56, 5 December 2012 (UTC)

It is based on monitoring patients who take the drugs. Pharmaceutical companies are required to collect information from patients and doctors about potential adverse effects of all the drugs they sell. Suicidal ideation is observed, but homicidal thoughts are not. 148.177.1.210 (talk) 19:02, 5 December 2012 (UTC)

Suicidal thoughts are a typical symptom of depression. So is a lack of motivation. If an antidepressant helps with motivation when the suicidal thoughts are still there, the risk of suicide goes up. Homicidal behavior is generally not associated with depression, so there are unlikely to be homicide-related effects of antidepressants. 148.177.1.210 (talk) 19:05, 5 December 2012 (UTC)

The premise is wrong. As the word "may" indicates, there is no certainty that these drugs cause suicidal ideation -- there is only some limited evidence to support that possibility. There is also no certainty that they don't cause homicidal ideation -- there just isn't any significant quantity of evidence to support that possibility. Looie496 (talk) 21:57, 5 December 2012 (UTC)

A person may find it less objectionable to admit to having urges to kill oneself than to admit to having urges to kill another person. Bus stop (talk) 22:23, 5 December 2012 (UTC)

A person might be given the possibility of reporting anonymously. OsmanRF34 (talk) 14:21, 6 December 2012 (UTC)

Using your reasoning suicide rates and homicide rates must be highly correlated in every country then. Dncsky (talk) 02:00, 6 December 2012 (UTC)

I don't understand your point. Bus stop (talk) 02:21, 6 December 2012 (UTC)

He's using reductio ad absurdum in order to demonstrate to the OP why his assumption is wrong. 146.87.49.23 (talk) 08:56, 6 December 2012 (UTC)

That still doesn't make sense. The OP is not saying that antidepressants cause suicide and homicide ideation. He's only asking if they are tested for that. Even is antidepressants caused both, the correlation wouldn't be between suicide and homicide, but between use of antidepressants and the combining number of suicide and homicide. OsmanRF34 (talk) 14:21, 6 December 2012 (UTC)

Did you read what the OP said? They specifically said 'Logically, presuming that "this may caues you to care less than you currently do about your own life" it would follow that it might also "cause you to care less than you currently do about a random stranger's life'. Nil Einne (talk) 16:24, 6 December 2012 (UTC)

So the question becomes: is a person who has suicidal thoughts more likely to also have homicidal thoughts than a person who has neither?165.212.189.187 (talk) 13:18, 6 December 2012 (UTC)

I don't think the reference desk can give a meaningful answer to that question. Obviously drugs (antidepressants) are tested by pharmaceutical companies for potential side effects. The question immediately above does not even mention antidepressants. Is that your intention—to eliminate antidepressants and other pharmaceuticals as a factor in the question that you are posing? I don't think we can just determine whether there is a correlation, and what that correlation might be, between thoughts of suicide and thoughts of homicide. It should be noted that homicide and suicide can occur together. Bus stop (talk) 18:53, 6 December 2012 (UTC)

Sure, if it helps you to conceptually compartmentalize the components and then retro fit the two later. Once you answer the q immediately above you can use logic: A therefore B therefore C = A therefore C. Right?165.212.189.187 (talk) 19:49, 6 December 2012 (UTC)

No. I am not trying to "compartmentalize" anything. I think you asked a great question. I'm referring to your first post. I think most of the responses were faulty in some ways. But I may have felt that most of the responses that other editors gave to your initial post were faulty because I perhaps misunderstood the thrust of your first post. After other editors devoted much discussion to teasing out the final iota of meaning from your first post, you re-posted a question. At that point I felt compelled to respond to your newly formulated question. As I indicated in my first post, I wonder about how one would go about collecting this information, and whether there may be a differential between the ease of collecting information on homicidal and suicidal thoughts. Bus stop (talk) 21:02, 6 December 2012 (UTC)

Sounds plausible. OsmanRF34 (talk) 14:21, 6 December 2012 (UTC)

Wellbutrin comes with a warning of a potential side effect of "homicidal ideation"[4]. Bus stop (talk) 17:59, 6 December 2012 (UTC)

why is it that advantageous for RBCs not to have nuclei?

Wouldn't it be more cost-effective if RBCs could repair themselves? It seems to me that the cost of constantly making RBCs would be more than the benefit of the extra space. Or is the risk of oxidative damage and subsequent cancer so great that all bloodmaking is confined to the marrow? 71.207.151.227 (talk) 20:21, 5 December 2012 (UTC)

The big advantage is that you can pack a lot more hemoglobin into the same space, and the cells are much more flexible and able to squeeze through tight capillaries whike suffering less mechanical damage. That outweighs any benefit you get from self-repair. By the way, mammalian RBCs lack nuclei, whereas those of fish, amphibians, reptiles and birds have nuclei. Dominus Vobisdu (talk) 20:33, 5 December 2012 (UTC)

There is a correlation between nucleated red blood cells and poor prognosis in intensive care [5] though this doesn't speak to the direction of the causality. Our article red blood cell contains the interesting information, which I hadn't known, that enucleation of red blood cells has evolved three times independently in vertebrates. I would be tempted speculate about the increased need for circulation in warm-blooded mammals, except... birds do all that and more. Fundamentally, saying why evolution went a certain way is a rather speculative enterprise. Wnt (talk) 20:40, 5 December 2012 (UTC)

Sometimes speculative, sometimes not. Often, it's pretty easy to determine how an innovation is advantageous. You're quibbling with the word "why", which has two distinct meanings, one teleological, and one purely explanatory, closer in meaning to "how". The former lies outside of the scope of evolutionary science. The latter does not. It's rather easy to explain why (= how) a four-chambered heart is advantageous, or why (= how) enucleated RBCs are an improvement over nucleated ones. The problem starts when you start attaching a teleological sense to the word "why". Dominus Vobisdu (talk) 00:40, 6 December 2012 (UTC)

Enucleated RBCs are smaller, kind of not quite donut shaped rather than fried egg shaped, and it would seem to me can negotiate the tight constriction of the capillaries better. A lousy comparison, but look at the trouble sickle cells have. Even if not directly causing clots, rbcs with a larger cross section would require lower blood velocity, require larger capillaries, or get a lot more wear and tear bashing around the tight turns. "Cold-blooded" critters don't have the same oxygen requirements we do and presumably can deal with reduced blood flow, while birds on the other hand have a more efficient lung design which can presumably provide sufficient oxygen with reduced blood flow from the "oxygen push" side. Plus the raw material of rbcs is largely recycled anyway. (Entirely guessing all this on my part, i should mention) Gzuckier (talk) 02:10, 6 December 2012 (UTC)

• Nuclei are metabolically costly and exist to (1) express proteins, and (2) undergo cell division. But red blood cells basically serve as a substance meant to convey oxygen. They don't need to reproduce since they are produced copiously by the marrow, and they don't need to express proteins because they are already packed full of hemoglobin and do their job best just by transporting oxygen as efficiently as as possible until they wear out and are replaced. μηδείς (talk) 03:21, 6 December 2012 (UTC)

One could argue that with the loss of the nucleus and the related cell maintenance and division functionality, they are no longer real cells at all - just passive "packaging" for the heamoglobin. Roger (talk) 09:56, 6 December 2012 (UTC)

That's why I called them a substance. μηδείς (talk) 16:46, 6 December 2012 (UTC)

That is a position some people take, who believe in blood substitutes - unfortunately, this leads, over and over again, to people rewriting the rules so they can experiment in injecting cut-rate substance into trauma patients, who die much more frequently than those receiving real blood. All so some corporations can save money/make money and avoid paying blood donors... which would be "unethical". I don't believe it for a minute. Red blood cells are alive - they are able to control their shape actively. [6][7] They have given up control of many processes via transcription, indeed even by translation after the reticulocyte stage, but for example our neurons don't use those processes for split second decisions. I suspect their ability to exhibit varied behavior is actually greatly underappreciated. Wnt (talk) 19:39, 6 December 2012 (UTC)

My comment was not any sort of advocacy. μηδείς (talk) 20:56, 6 December 2012 (UTC)

Phylogeny

This is more of a conceptual question about phylogeny. Looking at phylogenies, how do scientists know that ancestral species is still alive or not? What if the species is an marine invertebrate that was only present shortly and that was in an evolutionary arms race and became quickly extinct but its daughter lineages survived because those lineages could adapt to changing times and evade predation? What if we have no traces of the actual ancestor so we erroneously infer the "actual" ancestor as a extant species? How did adaptations evolve? Exaptation may explain how tetrapods may have colonized the land, but did adaptations initially arise spontaneously and by sheer luck those traits were favored than others and underwent adaptive radiation and diversified into many different forms? Were the initial mutants "hopeful monsters" and somehow the "hopeful monsters" were lucky enough to find mates because the mutations were rather common? Sometimes, evolution by natural selection can seem, well, miraculous. It's like "Ding! You got a new adaptive trait that was beneficial to you and you could successfully breed as much as you want!" 75.185.79.52 (talk) 23:14, 5 December 2012 (UTC)

To answer your questions in order:

1. Most phylogenies present an implicit assumption that the ancestor is long gone.
2. It is actually the usual case that there is no archaeological or other direct evidence of the ancestor.
3. "We" don't declare an extant species to be the ancestor, ever. It would more usually be stated something like "Species A is the closest living relative of Species B."
4. Randomly, although some organisms experience mutation faster than others, and some organisms may mutate faster under certain forms of stress.
5. See natural selection. Genetic changes that have no benefit to a species may become common anyway (see genetic drift and founder effect).
6. Generally the initial mutants are not suspected to have been "hopeful monsters". Rather, changes occur that are incrementally beneficial to an organism. See evolution of the eye for an example of how something quite complicated can come into being gradually.
7. It's true that more mutations are harmful than beneficial, and even more are just completely pointless (see silent mutation, for example). But when you have organisms multiplying in great number all over the planet for countless generations, it's OK to be terribly inefficient. If you mutate enough animals, it's simply inevitable that one of them will get some kind of improvement. Someguy1221 (talk) 00:01, 6 December 2012 (UTC)

Good job I checked before I posted my mini-essay of an answer :) Yours is a much more concise answer! lol. douts (talk) 00:15, 6 December 2012 (UTC)

A related matter; debating evolution wih a person of normal intellect who nevertheless was an evolutionary skeptic, it became clear that his position was that in cases where the sequence of speciation is recorded, such as the evolution of the horse from eohippus, that in fact that is a species evolving within itself, rather than new species being created and the parent species becoming extinct. Does it all really depend on our definition of speciation? I mean, we argue that Great Danes are the same species as the ancestral canis familiaris that first ate our garbage, but the possibility that they could interbreed is still speculative, no? Gzuckier (talk) 02:20, 6 December 2012 (UTC)

I'd call it an educated guess with a rather convincing argument. It's the case that most extant breeds to descend from the ancestral Canis lupus familiaris can successfully interbreed, so it stands to reason that most/all of those extant breeds could hypothetically interbreed with that common ancestor. The extant breeds can even mate with familiaris's nearest neighbor, the Grey Wolf, which is rightly considered the same species as the domesticated dog. It would be rather remarkable, nay, paradoxical, if two subspecies could interbreed with one another, but not with an ancestor that post-dates the MRCA. Someguy1221 (talk) 02:34, 6 December 2012 (UTC)

Along those same lines, I am of the opinion that when everyone agrees that three organisms (one ancestral and two extant descendants) are the same species, they are probably correct. Far more difficult than arguing two organisms could interbreed is arguing that they could not. To this day, it's not clear if Neanderthals were actually a distinct species from humans; everyone agrees that reproductive isolation between humans and neanderthals was at least the norm, but that can arise from geographical isolation and selective breeding just as easily as it can arise from actual speciation. Someguy1221 (talk) 02:44, 6 December 2012 (UTC)

The idea of the "hopeful monster" has gone out of fashion in evolutionary circles, rather too far out of fashion, I think. It is true that many mutations of large effect favored by artificial selection or presenting in rare individuals seem never to be important in long-term evolution because they are too generally problematic - there are six-fingered people, six-fingered cats, but no six-fingered species of mammals. Nonetheless, our genomes bear the evidence of whole genome duplication, chromosomal rearrangement and so forth on quite a few occasions over the course of many millions of years, and while one assumes many of these were nearly invisible as they occurred (like naturally occurring lineages of fruit flies with paracentric inversions), I'm skeptical that they all were. Hopeful monsters as a step in evolution are definitely exceedingly rare - any putative brand new hopeful monster you find in the wild, however well adapted, almost surely has no real chance of starting a new species. But I think it's still possible that looking backward, at those few that did make it, we might see evidence of their impact. That, however, is an overly indulgent view toward the idea by most standards. Wnt (talk) 15:49, 7 December 2012 (UTC)