Wikipedia:Reference desk/Archives/Science/2014 December 5

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December 5

Does punctuated evolution provide an explanation for the lack of transitional species?

Put it another way, did the ancestral bacteria really have to look like or function like modern bacteria with all its gene regulation mechanisms? Could it be that in a primitive form, bacteria that cannot regulate genes efficiently die out while bacteria that can do so survive and divide? Is it still called bacteria or life, though, if a living organism cannot consume food or make food? Could there have been a jump (punctuated evolution) in the very early part of the evolutionary tree? To put into context, I am trying to imagine a primitive version of the lac operon or the stop codon. Is it possible to have punctuated evolution to work this way? Organic molecules that stop the gene transcription are beneficial in the long run and continue to do so, whereas organic molecules that fail to stop the gene transcription are not beneficial and thus degrade and fall into oblivion (hence not alive)? Or am I missing the point of punctuated evolution? 71.79.234.132 (talk) 06:21, 5 December 2014 (UTC)

Did you read punctuated evolution ? Does it answer any of your questions ? In any case, very few bacteria from the beginning of life would be expected to still exist in fossilized forms today. StuRat (talk) 06:58, 5 December 2014 (UTC)

I said transitional species, not necessarily transitional fossils. 71.79.234.132 (talk) 11:47, 5 December 2014 (UTC)

The operon model is one technical method by which one gene can regulate another, but not the only method. It seems hard to picture, but there are so many generations of prokaryotes, with constant mutations that include large-scale DNA rearrangements, that any two genes will eventually be found next to one another, and if that happens to give the resulting bacterium an advantage, then they stay together and evolve on from there. Bacteria are exquisitely sensitive to waste of resources - even a single unnecessary gene will pretty rapidly be purged from a population of them simply to save the time and nutritional expense of copying its DNA. So they prefer (i.e. evolve) mechanisms by which a whole region can be regulated at once with one molecule from one regulatory gene when they can. Wnt (talk) 12:38, 5 December 2014 (UTC)

That answers my question.71.79.234.132 (talk) 12:53, 5 December 2014 (UTC)

There is no such thing as a lack of transitional species. You yourself are a transitional species right now. Every species of anything that has ever existed is a transitional species. --OuroborosCobra (talk) 13:19, 5 December 2014 (UTC)

That's not true under punctuated evolution, where most species are in stasis, and only a small portion are in a period of major transition at any time, although all animals, including humans, no doubt are currently undergoing some minor evolution, like in resistance to disease. StuRat (talk) 15:37, 5 December 2014 (UTC)

An example can be found with Heliconius. Like many other butterflies, they have wing patterns that try to resemble other, inedible, butterflies in the same geographical region. What's interesting is that they cover a wide area and actually copy multiple butterflies depending on the region. So you have evolution that "jumps" between these different goals, since a half-and-half is more or less useless, yet there are half-and-half individuals in hybrid zones, and so it appears that even at the genetic level the mechanisms by which color is determined get adapted to try to match one or the other more readily than being more intermediate ("supergene", which come to think of it has certain features in common with an operon, and indeed the uselessness of half-antibiotic-resistant bacteria might be another big reason behind operon organization). None of this actually means that DNA has any magic power to turn off background radiation and quit mutating; the jumps are at the level of appearance only. Wnt (talk) 16:41, 5 December 2014 (UTC)

Since you mention the start of life you might like to read our article on abiogenesis. I've always liked Stuart Kauffman's work on the topic, which is organized around the themes of self organization and emergent phenomena through the basic concept of the Autocatalytic_set. I recommend his books "Origins of Order" (if you know a decent amount of biochem and math) or "At Home in the Universe" at a more popular science level (though it is accessible it is still fairly deep). SemanticMantis (talk) 16:03, 5 December 2014 (UTC)

I'm no expert but I think Stephen J Gould was a fraud. Asmrulz (talk) 16:41, 5 December 2014 (UTC)

• First, I am not sure that you are using punctuated equilibrium in the way Gould Meant it. He simply meant that speciations are likely to occur when small populations enter a new environment, where there's a strong selective pressure leading to a rapid differentiation that we may not see happening in the fossil record because it occurs rapidly and in a small group. The concept "hopeful monster" seems closer to what I am saying, if I understand you correctly.

Another concept of importance is polyploidy. This happens in eukaryotes when they get more than the normal copies of genes. If, say, there were a gene that allowed the efficient metabolism of one sugar and the inefficient metabolism of a second sugar, having multiple copies might mean that a mutation in one of the copies that makes it less efficient at metabolizing the first sugar, but much more efficient at metabolizing the second sugar would benefit the organism. Not going into all the details, eventually we would say the one gene had become two separate genes with separate functions.

Finally, I'd suggest you read Stuart Kauffman's Origins of Order, which gives a good theory of how life could have arisen "metabolism-first" with self-replicating molecules coming along later. μηδείς (talk) 17:43, 5 December 2014 (UTC)

"Polyploidy" refers to complete sets of duplicated genes, which often happens in some plants and many bacteria / single-celled organism but is rare in multi-cellular animals. In animals, most episodes of gene duplication happen by other processes and involve only a few genes at a time, which would not be described as polyploidy. Dragons flight (talk) 18:06, 5 December 2014 (UTC)

Me? I didn't say a word of "punctuated" anything Asmrulz (talk) 19:24, 5 December 2014 (UTC)

I think Medeis was replying to OP. The problem is you that didn't follow WP:INDENT - when you write at the top level like that, everything that is properly indented looks like it is a response to you. Also consider that you comment wasn't terribly helpful, as it contained no references, and accused a well-respected and highly educated scientist of being a fraud, while also admitting that you have no special knowledge of the topic. SemanticMantis (talk) 20:09, 5 December 2014 (UTC)

Medeis brought up Gould, whom 71.79... or anyone else at that point in the thread, hadn't mentioned once. I agree with all of what you say about my comment, but that's all I wanted to say. You can't convince anyone of anything on the internets and anyway, there's always Google. "Whoever has ears to hear" and "sapienti sat" Also, my problem with Gould is not so much punctuated equilibrium as all the other stuff of his Asmrulz (talk) 20:25, 5 December 2014 (UTC)

Asmrulz, it was you who first mentioned Gould, in a post an hour before mine. I did not respond to you at all, since there was nothing of any consequence to respond to. Give PE was Gould's big idea, I did mention that I thought the IP was not using it the way Gould meant it. So I responded to him at length in a bulleted response to make it clear my answer was after but not in response to your ejaculation. Yes, DF, there are other ways genes are duplicated, that's why I said "not going into all the details". μηδείς (talk) 21:27, 5 December 2014 (UTC)

no prob. I just wondered why "Gould" and not "Eldredge and Gould," or why what Gould meant by p.e. matters so much for a theory that is 40 years now (there presumably has to have been some development since then) that you mention him in your reply to 71.79... if you didn't think they and me were the same person. re e**culations: I wanted to post a nasty retort and trust me I could, but I won't because you gave me a helpful advice once (I didn't need it in the end, but still) I'm sh**ng up before this gets too meta. sorry for the wrong indentation and sorry to the original poster for derailing their thread. Asmrulz (talk) 23:50, 5 December 2014 (UTC)

Because most non-biologists haven't heard of E. I wasn't worried about your indentation, and I believe I actually used the term ejaculation correctly, so be placated. My apologies also to SM, who gets priority on having mentioned Stuart Kauffman and his brain changer. μηδείς (talk) 23:54, 5 December 2014 (UTC)

Moment in a prestressed concrete beam

If you're trying to find the moment due to self weight in a prestressed concrete beam of known dimensions and known prestressed force, is it correct to use the equation Moment=Prestress Force(section modulus/area+Eccentricity) to find this?194.66.246.119 (talk) 17:06, 5 December 2014 (UTC)

Why does "Specific receptor binding" occur with drugs that are extremely small (such as Lithium)?

194.114.146.227 (talk) 19:48, 5 December 2014 (UTC)

Actually, lithium treatment is a pretty bad example of specific receptor binding -- the doses given are very high, with a small therapeutic ratio. It weakly affects several different processes so that it is a matter of continuing research which are most important. What is interesting is that small doses of lithium have been reported on occasion to have beneficial effect (see the article) and this suggests that a more specific process might exist (though it wouldn't be very relevant for the high-dose treatment because whatever receptor might remain to be discovered is already saturated at ineffectively low dosage). But if so, the receptor for that remains unknown.

In general, molecules like calmodulin or vanabins are arranged to provide just the right fit for a particular ion. Usually you can identify such molecules pretty easily with a radioactive isotope of the ion in question; by purifying the radioactivity you purify the bound protein. But the isotopes of lithium include no radioactive option with a half-life longer than a second! Where we are with understanding lithium is sort of a window on where we'd be in biology if radioactivity hadn't been discovered and put to use, I would suppose. Wnt (talk) 22:08, 5 December 2014 (UTC)

I think it's a matter of small molecules. See here.194.114.146.227 (talk) 11:28, 6 December 2014 (UTC)

Einstein's theory

Hello everyone,

Gravitation

$\Delta \tau _{g}={\frac {g}{c^{2}}}\sum _{i=1}^{k}(h_{i}-h_{0})\Delta t_{i}$

How the difference between 0m and 5000m on Earth should be today:

$\Delta \tau _{g}={\frac {~10}{9*10^{16}}}(5000m-0m)4.5*10^{9}years=21.9hours$

Why general relativity doesn't match with positions of the moon between 0m and 5000m?

Thank you for your answer.N738139 (talk) 23:27, 5 December 2014 (UTC) — Preceding unsigned comment added by N738139 (talk • contribs) 23:26, 5 December 2014 (UTC)

Exactly what do you believe you have calculated, and why do you believe it corresponds in any way to a position of the moon?

While it is very easy to take a standard equation of advanced physics and trivially plug and chug a value, part of being a physicist is knowing what equation to use, knowing what it actually means, and using it appropriately to make meaningful prediction. What you have done, in simple terms, is presented some meaningless arithmetic (alongside a mildly pleasing smattering of the greek alphabet for, I suppose, purely aesthetic purposes). This equation, in isolation, does not predict the passage of time, the position of the moon, or anything else. Nimur (talk) 23:49, 5 December 2014 (UTC)

t(i) are time stayed in different altitudes (h(i)) and Tau(g) is the shift difference we should observe with gravitation. (equation taken from another wiki about gravitation) Try with one day and you will see that the difference is nearly 50nanoseconds (what was observed with experiments).N738139 (talk) 00:08, 6 December 2014 (UTC)

Position of the moon or sun doesn't matter. If you want you can say number of day.N738139 (talk) 00:05, 6 December 2014 (UTC)

If you're trying to make sense of the fact that observers at two different locations can measure two different durations of time, then you can start by reading time dilation and relativity of simultaneity.

Relativistic theories of gravitation correctly predict that different locations will measure different durations of time between observed events. The mathematics of general relativity laboriously work out the painstaking details to make sure all these observations are consistent. Nimur (talk) 00:16, 6 December 2014 (UTC)

Thank you for your answer. I know a better wiki article to answer http://en.wikipedia.org/wiki/Gravitational_time_dilationN738139 (talk) 00:21, 6 December 2014 (UTC)

The moon's position changes with time, and since you calculated different time intervals at 0m and 1000m its easy to get confused and deduce separate positions for the moon as a result. But you are calculating time for clocks located at these different locations, such that they tick at different rates, with the 0m clock ticking slower within its location than the 1000m clock. Thus, the number of lunar cycles per 0m clock cycles (which will be fewer in number due to its slowness) is greater than the number of lunar cycles per the 1000m clock cycles counted. -Modocc (talk) 00:28, 6 December 2014 (UTC)

OK. Thank you. So "the number of lunar cycles per 0m clock cycles (which will be fewer in number due to its slowness) is greater than the number of lunar cycles per the 1000m clock cycles counted." N738139 (talk) 00:39, 6 December 2014 (UTC)

So a day per 0m clock cycles is greater than a day per the 1000m clock cycles counted ? N738139 (talk) 00:48, 6 December 2014 (UTC)

N738139, based on your previous question, I assume that you are asking why two observers, one at the base of a 5000 m summit and on at the top, don't see the moon in different positions?

Consider the following thought experiment. Methuselah-One and Methuselah-Two synchronize their watches and set an alarm for 4.5 billion years in the future. Methuselah-One climbs to the summit and patiently waits while his twin does the same at the base. When their alarms go off they both record the position of the moon. Methuselah-One then climbs back down and the twins compare their observations, and yes, these observations will differ by how far the moon moves in 21.9 hours. (I'm assuming your math is correct.) But when they compare their watches they will find that they differ by 21.9 hours as well. They saw the moon in different positions because they took their observations at different times. Even though the times were exactly 4.5 billion years from a common starting time, they spent most of that time in different reference frames and thus experienced a different rate of time flow compared to one another. If they resynchronize their watches and schedule a redo of the experiment in 24 hours, they will observe the moon in nearly the same location as one another because they will not have been separated from one another long enough the experience any measurable time slip.

Have your read Twin paradox, which deals with the special relativistic version of your general relativistic problem? Your question is a really good one which shows some insight, so make sure you understand your mistake before you give up. -- ToE 00:55, 6 December 2014 (UTC)

OK. So if I compare two stones (imagine a stone with a watch that I remember the sky they watched at last), I "will find that they differ by 21.9 hours as well." I totally agree with you if we consider general relativity. N738139 (talk) 01:03, 6 December 2014 (UTC)

In reply to your follow up question about the length of day above. Yes. For instance, a single Earth day measured by 24 clock hours is the ratio 1:24 or one day per 24 hours. But if a clock ticks at a slower rate, say x hours, this ratio in fact differs such that 1/x > 1/24. -Modocc (talk) 01:11, 6 December 2014 (UTC)~

This is an important part of the answer as well. The Methuselah twins' ultra-precise wrist watches kept time based on a local phenomenon, as does an atomic clock. They are not keeping time by observing the passage of the days (sunrise / sunset) or years (astronomical seasons), and the twins will disagree (very slightly) about the length of a day or a year. (We don't need practical engineering equipment to conduct a thought experiment, but it is interesting to see that the best case modern Atomic clock#Evaluated accuracy is 2.3 x 10⁻¹⁶, which multiplied by 4.5 x 10⁹ years yields only about 30 seconds.) -- ToE 01:39, 6 December 2014 (UTC)

30seconds?N738139 (talk) 02:05, 6 December 2014 (UTC)

I was just noting that our best atomic clocks have an accuracy on an order of 30 seconds per 4.5 billion years. (2.3 x 10⁻¹⁶ ⋅ 4.5 x 10⁹ years ⋅ π x 10⁷ seconds/year (close enough for an astronomer)) This has no relevance to your question other than wondering if the Methuselah twins' watches could be sufficiently accurate given current technology. They certainly wouldn't be sufficiently durable, but the twins wouldn't be either. -- ToE 03:57, 6 December 2014 (UTC)

Does that mean that the shift of our two clocks will be 21.9 hours + or - 30 seconds in 4.5 billion years in the future, if they would be sufficiently durable (by replacement)?N738139 (talk) 06:41, 6 December 2014 (UTC)

With one at the base of the mountain and one at the top? Yes, in spirit. But your 21.9 hours does not have enough significant digits for 21.9 hours + or - 30 seconds to be meaningful. Plus I believe that you have only taken into account the general relativistic effects of the change in the local gravitational acceleration, and not the special relativistic effects of the different rotational speeds. Note that I was simply trying to assist with the understanding of your results, and I have not verified your formula or mathematics, leaving that to the others here. The special relativistic effects will counter the general relativistic ones, but only to a small degree. -- ToE 11:29, 6 December 2014 (UTC)

Somewhere here we should link to Hafele–Keating_experiment#Equations. -- ToE 11:33, 6 December 2014 (UTC)

My opinion is that only Sagnac effect is the cause of a shift of cesium clock (working with light) and there is no time dilation. With time dilation our skies should have at least 1 minute more at 5000m than 0m (If we consider that 50 nanoseconds were observed during 1 year maximum). But I can be wrong. Whenever, if you read "On the Electrodynamics of Moving Bodies", you see that Einstein develops it arguments of a moving particle only in one direction/referential (v+k) not the other (v-k) (with which you would have space and time augmentation and not dilation. Depending where you are watching.) Anyway, thank you ToE for your excellent argumentation. N738139 (talk) 12:54, 6 December 2014 (UTC)

OK. OK. Thank you everyone. N738139 (talk) 01:14, 6 December 2014 (UTC)