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Thread: Genetic diversity in human evolution - does it make sense?

  1. #1 Genetic diversity in human evolution - does it make sense? 
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    My first post here, just had a thought that led to a question and wondered if anyone would know... (Palaeobiology exam tomorrow, would make a nice point to include)

    One piece of support for the single-origin out of Africa hypothesis of modern sapiens is the fact that the genetic diversity of African populations is higher than that in European and Asian populations (I believe that much of the support for this comes from studies such as the HapMap project, which found that the Yoruba have unusually short haplotype blocks, demonstrating less linkage and hinting at more ancestral recombination).

    However, just because that population has been around for longer, why would the genome of a population sitting still be subject to more recombination than that of one that is in the process of migrating? If European populations originate from African populations, they obviously trace their ancestry back an equal amount of time (as does all life on Earth, I suppose). Incidentally I think the out-of-Africa hypothesis holds weight, but this particular line of evidence just seems a little odd.

    Can anyone explain this?


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  3. #2 Re: Genetic diversity in human evolution - does it make sens 
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    Quote Originally Posted by Crayfish
    However, just because that population has been around for longer, why would the genome of a population sitting still be subject to more recombination than that of one that is in the process of migrating? If European populations originate from African populations, they obviously trace their ancestry back an equal amount of time (as does all life on Earth, I suppose). Incidentally I think the out-of-Africa hypothesis holds weight, but this particular line of evidence just seems a little odd.
    Think of the twin paradox. The greater the rate of motion through space, the less the rate of motion through time. Sitting populations undergo less motion through space, and therefore undergo greater motion through time. Your first sentence recognizes that one population has been around longer. It is therefore older in time. That should answer your own question. Your question stems from the mistaken assumption, in my opinion, that you make regarding tracing their ancestry back an equal amount of time. On what basis do you state that the amount of time of a population in migration over large periods of time is somehow equal to the abount of time of a population that is not in motion over large periods of time? Where you state above that you "suppose" is where I would recommend that you reconsider.


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    Each individual member of a population sitting still would be in motion daily and so would still be subject to this paradox. At the sort of speeds we're considering i.e. walking pace, even assuming that one population was literally immobile on an individual level this would still not have a significant effect enough to explain the observed disparity between diversity in African populations and other world populations.

    Except for small permutations as created by this physical law, all life on Earth can (hypothetically) be traced back to a single originating member or population and thus has an ancestry of equal length. I'm not a physicist and don't know the calculations involved, but I doubt that this can account for an actual time difference of more than a few seconds in a million years? All life is of course moving at the speed of the Earth and a few miles an hour plus or minus to this speed surely can't make much difference, or we'd be able to observe this effect ourselves.
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    Quote Originally Posted by Crayfish
    Each individual member of a population sitting still would be in motion daily and so would still be subject to this paradox.
    True. However, I believe that the difference is quite significant between peoples in motion over thousands of miles in space, out of Africa, over thousands of years of migration, versus people who were absent all of this motion and engaged in motion only in a manner completely compensated for by analogous motion by the migrating peoples.

    At the sort of speeds we're considering i.e. walking pace, even assuming that one population was literally immobile on an individual level this would still not have a significant effect enough to explain the observed disparity between diversity in African populations and other world populations.
    Please explain how you know this to be true.

    Except for small permutations as created by this physical law, all life on Earth can (hypothetically) be traced back to a single originating member or population and thus has an ancestry of equal length.
    This statement is common among linguists and anthropologists, who ignore the physics involved.

    I'm not a physicist
    This explains why you ignore the physics involved. You are considering time as an objective measure, using what I consider to be an irrelevant and unrelated unit, the cycle of the year. You are completely ignoring the relationship of space to time, as space-time.

    and don't know the calculations involved, but I doubt that this can account for an actual time difference of more than a few seconds in a million years?
    Wonderful. You are saying that you do recognize the phenomenon involved. Therefore, we area not disagreeing over the phenomenon, but our only difference of opinion is the degree of effect.

    All life is of course moving at the speed of the Earth and a few miles an hour plus or minus to this speed surely can't make much difference, or we'd be able to observe this effect ourselves.
    Let us get back to physics, where this question belongs. All of life, everything in the universe, moves at the same rate of speed, as there is only one rate of motion in the universe, the speed of light. I think that the question boils down to the relationship between the spatial and temporal components of the speed of light.
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    The way I've always seen it is exactly this:
    Generally, the further one migrates, the more isolated one becomes.

    Does not diversity imply aggregation from a multifarious population?



    Surely though, I cannot for the life of me figure out how C figures into this. However, I suggested to myself that I might take no fewer than several perscription drugs tonight, ergo, it is ultimately possible that all of you are figments of my imagination anyway. If the case is such, I fully understand.
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    Quote Originally Posted by CaveatLector
    The way I've always seen it is exactly this:
    Generally, the further one migrates, the more isolated one becomes.
    I don't understand. Can you rephrase this?

    Does not diversity imply aggregation from a multifarious population?
    Can you rephrase this?

    Surely though, I cannot for the life of me figure out how C figures into this.
    This is understandable. It is common to think of this not in terms of space-time, but in terms of space as distinct from time. With such thinking, my arguments can make no sense. You must understand the significance of space-time in order to come to understand the relationship between space and time. Without this, it is common to believe as you stated, that all people are the same age, such that the change in motion through space has had no effect on the unrelated concept of motion through time. With an understanding of the nature of space-time, then it is possible to recognize that differences in motion through space, such as migration, have resulted in differences in motion through time. The various races of our species are not genetically at the same temporal position, or age, and this can account for numerous physical, cultural, and linguistic differences among the species.
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    My most sincere and heartfelt apologies, Mr. or Mrs. Hermes.
    It seems that, while I may make attempts at presenting coherent and lucid thoughts, the bulk of my previous comment occasioned more attractiveness than actual substance. As much as I hate to admit it, which is exactly equal to not at all, at times this phenomenon is acutely fashioned to the behavior of the over-medicated. Please excuse any declamatory style in the future lacking decipherability.

    Here are the comments, altered for the reader’s comfort.

    Does not diversity imply genetic aggregation from a multifarious population?
    Generally, the further a group migrates, the more genetically isolated said group becomes.


    Hope this helps.
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    Quote Originally Posted by CaveatLector
    Does not diversity imply genetic aggregation from a multifarious population?
    Generally, the further a group migrates, the more genetically isolated said group becomes.
    I think that it is considered that the populations that migrated the farthest and earliest from Africa exhibit the least genetic diversity. Is that your point? If so, or not, what conclusion do you draw that is significat to this topic?
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    Quote Originally Posted by Hermes
    I think that it is considered that the populations that migrated the farthest and earliest from Africa exhibit the least genetic diversity. Is that your point?
    Not as a rigid rule, but yes.
    It is undoubtedly possible that genetic isolation discourages diversity.

    what conclusion do you draw that is significat to this topic?
    I am genuinely shocked that the same question has not been asked of you, Mr. or Mrs. Hermes.


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    Whatever you two guys (or gals) are on is probably illegal in most countries! 8)
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    Isolation could be a possible explanatory mechanism, but it seems coincidental that each migratory population should be similarly isolated (Asian and European populations have similar levels of diversity). Perhaps this could be evidence against significant (an important leaning?) gene flow between African and 'newer' populations though.

    The only problem with the isolation hypothesis is that haplotype blocks in the Yoruba are not only more diverse but also physically shorter than other populations. This would imply more ancestral recombination - now it's possible that a small founder population e.g. in Europe might explain the relatively fewer modern haplotypes, but why would they also be larger?

    This problem is vexing me now, a reasonable explanation escapes me. The physical space-time explanation would in fact be the best I've heard, were it not for the relatively minor effect it's likely to have. We are after all talking about a time scale of no more than 160 thousand years or so, and a difference that would equate to several hundred or more generations.

    Other mechanisms that I can think of are that the higher insolation, dietary considerations or possibly shorter lifespans/generation times may have favoured recombination in African populations. The increased levels of UVA oxidative damage could even be envisaged to increase the rate of single base substitution, which would have the effect of shortening haplotype blocks. Still not satisfactory though.
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    Quote Originally Posted by Crayfish
    The physical space-time explanation would in fact be the best I've heard, were it not for the relatively minor effect it's likely to have. We are after all talking about a time scale of no more than 160 thousand years or so, and a difference that would equate to several hundred or more generations.
    I personally do not care if you buy this explanation or not. However, I disagree that the effect is as minor as you seem to conclude. We seem to agree on the possibility of such an effect, yet you would drop it because of your assumptions about physics that lead you to assume tht you should disagree on the degree of the effect. Why must there be a difference of several hundred generations? In other words, why can there not be temporal differences within the respective generations as well? You seem to be stuck on the notion that each individual, or each group of our species, for some reason must have the same basic rate of motion through space-time.
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    Frankly, I think we should forget about relativity. Populations in africa also wer eont eh mvoe, jsut traveling back and forth, to say so. Also htink about this, shouldn't birds and orher migrative animals evolve slowly? They do travel far more than huma. Also, once you really start tinkering with the numbers.... well, your average scientific calculator can't just dispaly the result of the first division. it STILL is zero, point, zero after 99 decimals. (That was when I tried to calculate for fun what "delay" would had got an airliner commander after flying 48,000,000 seconds at some 250 m/s. My calculator dumped zero as the number was smaller than 1/ 1 x 10-99 seconds of delay).

    Remember, the delay is proportional to speed, distance is irrelevant. BTW, you hadn't accounted that people closer to the poles are traveling all their life at a speed slower than those closer to the equator... the difference are some 250 km/h between the equator and New York, fai.
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    Quote Originally Posted by Lucifer
    Frankly, I think we should forget about relativity.
    Frankly, I think that you should forget about relativity.

    Populations in africa also wer eont eh mvoe, jsut traveling back and forth, to say so. Also htink about this, shouldn't birds and orher migrative animals evolve slowly?
    What evidence do you have that they do not?

    Also, once you really start tinkering with the numbers....
    How do you claim to know what happens once I start tinkering with the numbers? Speak for yourself.

    well, your average scientific calculator can't just dispaly the result of the first division. it STILL is zero, point, zero after 99 decimals. (That was when I tried to calculate for fun what "delay" would had got an airliner commander after flying 48,000,000 seconds at some 250 m/s. My calculator dumped zero as the number was smaller than 1/ 1 x 10-99 seconds of delay).
    Do you think that your calculation is accurate?

    Remember, the delay is proportional to speed, distance is irrelevant.
    Not completely. You seem to forget that migration takes time, and this time has an effect on the change in time.

    BTW, you hadn't accounted that people closer to the poles are traveling all their life at a speed slower than those closer to the equator... the difference are some 250 km/h between the equator and New York, fai.
    I find it interetsting that you can tell me what I account for and what I do not, what I remember and what I do not, and what I should think relevant and what I should not. I think that you should state what your opinion is, and let others come to their own conclusions. I think that your math is not particularly relevant, and that your conclusions based on it are not accurate.
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    Hermes, you are talking rubbish and have been for several posts. I'll apologise fulsomely if you show us your maths justifying the nonsense you are posting in this thread. I hope and half believe you are just amusing yourself. I find it difficult to believe you can be serious.
    So, please retract or demonstrate with figures.
    Thank you.
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    Hermes, you are talking rubbish and have been for several posts. I'll apologise fulsomely if you show us your maths justifying the nonsense you are posting in this thread. I hope and half believe you are just amusing yourself. I find it difficult to believe you can be serious.
    So, please retract or demonstrate with figures.
    Thank you.
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    Quote Originally Posted by Ophiolite
    Hermes, you are talking rubbish and have been for several posts. I'll apologise fulsomely if you show us your maths justifying the nonsense you are posting in this thread. I hope and half believe you are just amusing yourself. I find it difficult to believe you can be serious.
    So, please retract or demonstrate with figures.
    Thank you.
    Ophiolite, you seem to be trying to be funny. I feel sorry for your attitude.
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    No I am not trying to be funny. You have posted some statements that appear to suggest that Relativity and the variation of perceived time with velocity could somehow be relevant in relation to migrating humans. I am unaware of any rational characterisation of this that does not include the word nonsense, or a synomym of the same.
    Since I may have simply misunderstood your intention I have suggested you offer data to support this apparent nonsense, or retract your claims, or (and this is a third option) express yourself more clearly so that your sensible intent emerges and the nonsense blows away in the light of reason.
    The response you have offered appears to mean you are unable to justify your nonsense. In short, a de facto retraction.
    I would still prefer a definitive response that involved one of the three I have suggested:
    a) Provide susbstantial mathematical justification for your claim.
    b) Retract your claim.
    c) Clarify what it is you are actually claiming

    Edited for typographical errors.
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    First of all I am sorry Hermes but I am with Ophiolite on this one. Thinking that relativity is relevent here is too absurd to credit with seriousness.

    Quote Originally Posted by Crayfish
    However, just because that population has been around for longer, why would the genome of a population sitting still be subject to more recombination than that of one that is in the process of migrating? If European populations originate from African populations, they obviously trace their ancestry back an equal amount of time (as does all life on Earth, I suppose).
    You are missing the point, which is that the longer haplotype blocks in the rest of the world indicate a recent restriction of the gene pool to a much smaller group. The conclusion is obvious, that the rest of the world draws all of its ancestral genetic variation from a small sample drawn from the original much larger gene pool in Africa. This suggests that the human population of the rest of the world derives from a comparatively recent migration of a small population group originating in Africa (with very little genetic variety) that spread and reproduce rapidly. This is possible because of an exploration - nomadic lifestyle that prospered so well in the fresh game rich area of Europe and Asia that it rapidly filled the rest of the world while those who remained in Africa continued in a less prosperous equillibrium.

    Quote Originally Posted by Crayfish
    The only problem with the isolation hypothesis is that haplotype blocks in the Yoruba are not only more diverse but also physically shorter than other populations. This would imply more ancestral recombination - now it's possible that a small founder population e.g. in Europe might explain the relatively fewer modern haplotypes, but why would they also be larger?
    The haplotypes are physically shorter because of the greater gene pool not because of more ancestral recombinations. Recombination of nearly identical chromosomes produces very little genetic change and the haplotypes are naturally longer because of this.
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    Quote Originally Posted by Ophiolite
    Since I may have simply misunderstood your intention I have suggested you offer data to support this apparent nonsense, or retract your claims, or (and this is a third option) express yourself more clearly so that your senisble intent emerges and the nonsense blows away in the light of reason.
    The response you have offered appears to mean you are unable to justify your nonsense. In short, a de facto retraction.
    Your statement is quite silly, Ophiolite. Do you take yourself seriously? I recognize that you do not understand the implications of space-time. There is no problem with that. However, the poor attitude that you take in your reaction, together with this rather foolish rubbish that you post here about a de facto retraction, demonstrates that you most likely have very little ability put forward the effort required to understand the concept. I feel sorry for your attitude. You are attempting to project your weakness on me. I do not particularly care if you lack depth in your undertanding of the implications of space-time. If you take this as evidence that your are brilliant, then feel free. I see no reason to present my arguments in a manner that you claim that I absolutely must, just to avoid your criticism, as though obtaining your respect were the only goal of my argument. Perhaps you might do a little investigation into the nature of space-time, or else quite complaining to me about your lack of knowledge.
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    Quote Originally Posted by mitchellmckain
    First of all I am sorry Hermes but I am with Ophiolite on this one. Thinking that relativity is relevent here is too absurd to credit with seriousness.
    No need to be sorry. I realize that the concept of space-time is a difficult one to understand, and that physicists also have great difficulty understanding the implications. If you do not want to take the idea, insofar as you think that you understand my point, seriously, I do not mind at all.

    Just out of curiosity, do you deny completely the implications of migration through space on the rate of evolution through time, as reflected through the concept of the twin paradox, or is the issue the degree of the effect?
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    Quote Originally Posted by Hermes
    No need to be sorry. I realize that the concept of space-time is a difficult one to understand, and that physicists also have great difficulty understanding the implications. If you do not want to take the idea, insofar as you think that you understand my point, seriously, I do not mind at all.

    Just out of curiosity, do you deny completely the implications of migration through space on the rate of evolution through time, as reflected through the concept of the twin paradox, or is the issue the degree of the effect?
    Hermes, relativity is my area of expertise. Check my website. No velocity achievable by biological organisms is capable of producing a measurable time dilation. The cheetah at a maximum of 114 km/hr produces a time dilation which is only 1 part slower in 90 trillion time parts, which is a loss of only 1 second in 2.8 million years. This is hardly a significant factor in the phenomenon we are discussing.
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    Quote Originally Posted by mitchellmckain
    Quote Originally Posted by Hermes
    No need to be sorry. I realize that the concept of space-time is a difficult one to understand, and that physicists also have great difficulty understanding the implications. If you do not want to take the idea, insofar as you think that you understand my point, seriously, I do not mind at all.

    Just out of curiosity, do you deny completely the implications of migration through space on the rate of evolution through time, as reflected through the concept of the twin paradox, or is the issue the degree of the effect?
    Hermes, relativity is my area of expertise. Check my website. No velocity achievable by biological organisms is capable of producing a measurable time dilation. The cheetah at a maximum of 114 km/hr produces a time dilation which is only 1 part slower in 90 trillion time parts, which is a loss of only 1 second in 2.8 million years. This is hardly a significant factor in the phenomenon we are discussing.
    Duh, I would love to have your calculator, LOL!


    @Hermes: temporal dilation is proportional to VELOCITY. Things that move experience time at a slower pace; the faster they move, the slower their "perceived time" is compared to "beholder time". Now, all human move at similar velocity, well, not exactly, those closer to equator move faster than those closer to the pole. But relativity is neglectable at slow velocities, as its effect is too small. If you want to calculate time delation yourself, the formula is as follows:

    SQR(1-(v^2/c^2))

    Or, square root of 1 minus velocity square divided by c square.

    You multiply time for the result of this formula and you got how much time has experienced the traveler versus the time experienced by the observer.

    For a traveler moving at 0.9 c, time delay would be of 0.4358898944, that is, traveler would grow older 0.435etc seconds in each second of the observer's time. FAI, in an hour of observer time, the traveler would grow older by some 26 minutes and 9,202 seconds.

    In the case of a human being who was running (assume v= 8 m/s, or 28.8 km/h), it would be:

    SQR(1-(8^2/299,792,458^2)) = SQR(1-(64/8.987551787x10^16) = SQR(1-64/89,875,517,870,000,000) = SQR(1-0,0000000000000007120960359, or 7.120960359 x 10^-16) ... then your calculator will tell you that 1-0,0000000000000007120960359 = 1 and you won't be able to take the square root of the result.

    And, BTW, mitchellmckain's field of expertise are relativity physics. He knows his stuff, you don't.
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    Quote Originally Posted by Lucifer
    Duh, I would love to have your calculator, LOL!

    SQR(1-(v^2/c^2))

    Or, square root of 1 minus velocity square divided by c square.

    SQR(1-(8^2/299,792,458^2)) = SQR(1-(64/8.987551787x10^16) = SQR(1-64/89,875,517,870,000,000) = SQR(1-0,0000000000000007120960359, or 7.120960359 x 10^-16) ... then your calculator will tell you that 1-0,0000000000000007120960359 = 1 and you won't be able to take the square root of the result.
    I don't have a fancy calculator, a taylors expansion around v=0 gives you a formula that you can use to do the calculation all the way like I did. And I actually made an error when I did so and was off by a factor of 2. The correct answer in my example was 1 time part slower in 180 trillion time parts or 1 second slower in 5.6 million years.

    The formula I used was:
    gamma = 1/SQR(1-(v^2/c^2)) = 1 +.5 v^2/c^2 + (something around v^4/c^4)

    but you can also use this if you like
    SQR(1-(v^2/c^2)) = 1 - .5 v^2/c^2 + (something around v^4/c^4)

    (you can test these for v = 0.1 c)

    This way you can leave out the 1 so it doesn't annihilate the insignificant portion .5 v^2/c^2. The v^4/c^4 part can be ignored since we would only need it if we wanted our answer to 14 significant digits in my example or to 16 significant digits in your example.

    Using this on your example this gives 1 time part in 2/7.121x10^-16 = 2808 trillion time parts or 1 second every 89 million years
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    Quote Originally Posted by mitchellmckain
    Hermes, relativity is my area of expertise. Check my website. No velocity achievable by biological organisms is capable of producing a measurable time dilation. The cheetah at a maximum of 114 km/hr produces a time dilation which is only 1 part slower in 90 trillion time parts, which is a loss of only 1 second in 2.8 million years. This is hardly a significant factor in the phenomenon we are discussing.
    I see. You believe that if a family of cheetahs were to live out their lives never leaving a cave and another family were to run at full speed their entire lives, then in 2.8 million years of evolution the entire difference in their genetic age will be no more than one second. Do you also consider, based on your understanding of relativity, that the cheetahs in greater motion would not necessarily evolve through a greater number of generations in that time period, which might cause a greater rate of evolution of their genes?
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    Hermes,
    I had suspected that my understanding of your earlier posts was faulty. I did not truly entertain the notion that a (presumably) educated, literate person could imagine that any velocity achievable by an animal could have the slightest discernible effect upon the passage of time for them.

    Mitchell, an expert in these matters, has confirmed by calculation that the effect is so vanishingly small as to be irrelevant. This should be evident even to persons with little knowledge of Relativity. (Those with some knowledge would not consider such a dumb idea in the first place.)

    It appears that you do somehow believe that the effect could exist. Such a belief is groundless. I urge you to reconsider the material presented by Mitchell. At present you are simply making yourself look decidedly foolish.
    Ophiolite
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    Quote Originally Posted by mitchellmckain
    Hermes, relativity is my area of expertise. Check my website. No velocity achievable by biological organisms is capable of producing a measurable time dilation. The cheetah at a maximum of 114 km/hr produces a time dilation which is only 1 part slower in 90 trillion time parts, which is a loss of only 1 second in 2.8 million years.
    Since this is your area of expertise, I have a question for you. I am under the impression that your calculations are based on the cheetah being in a space ship, such that the cheetah would be at rest with respect to his point of reference. In other words, the cheetah could be asleep while the ship moved through space, and he would have the same effect. Is this so? If so, then is there any difference in a situation such as this, where the cheetah is not at rest with respect to his point of reference, but is moving all of the muscles in his body and exercising all of the cells in his body, and going through large amounts of oxygen and food? In other words, do you think that the time differential, no matter how insignificant you think it to be, would be identical were the object at rest with repsect to its environment for 2.8 million years or being the source of its own relative velocity for that same period?
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  29. #28  
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    Sorry for taking so long to get back to you on this. I am afraid that I am not in the habit of checking the biology threads too often.
    Quote Originally Posted by Hermes
    I see. You believe that if a family of cheetahs were to live out their lives never leaving a cave and another family were to run at full speed their entire lives, then in 2.8 million years of evolution the entire difference in their genetic age will be no more than one second. Do you also consider, based on your understanding of relativity, that the cheetahs in greater motion would not necessarily evolve through a greater number of generations in that time period, which might cause a greater rate of evolution of their genes?
    This is correct.

    Quote Originally Posted by Hermes
    Since this is your area of expertise, I have a question for you. I am under the impression that your calculations are based on the cheetah being in a space ship, such that the cheetah would be at rest with respect to his point of reference. In other words, the cheetah could be asleep while the ship moved through space, and he would have the same effect. Is this so? If so, then is there any difference in a situation such as this, where the cheetah is not at rest with respect to his point of reference, but is moving all of the muscles in his body and exercising all of the cells in his body, and going through large amounts of oxygen and food? In other words, do you think that the time differential, no matter how insignificant you think it to be, would be identical were the object at rest with repsect to its environment for 2.8 million years or being the source of its own relative velocity for that same period?
    The source of the velocity is irrelevant. In a ship or on foot the effect of the velocity is the same. The motion of parts of the body within the body is even more insignificant. The motion of the molecules due to heat is also insignificant in terms of relativity. The phrase "no matter how insignificant" is meaningless. If the difference is too small to measure in any way and has no impact on anything we can measure, then it might as well not exist at all as far as physics is concerned, for physics cannot talk meaningfully about something which cannot be measured.

    By the way there is a gravitational time dilation which causes a small but measurable difference in the rate of time flow between a clock on the surface of the earth and a clock out in space. This is due to the General Theory of Relativity which is Einstein's theory of gravity.
    See my physics of spaceflight simulator at http://www.relspace.astahost.com

    I now have a blog too: http://astahost.blogspot.com/
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    Thanks Mitchell, that makes perfect sense (blindingly obvious actually, in hindsight )

    Hermes, your persistence is admirable but I'm afraid you seem to be stuck in a slightly dead end nonsensical rut. And when did space ships come into it? I'm sure there are forums somewhere for wild speculation and baseless pseudoscientific ramblings.
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    Far too late for your exam, but as best as I can figure it out diveristy of a popluation is dependent upon the number of indiduals that have contributed to the genome. This number increases with time.

    So modern humans arise in Africa 150 million years ago (mya), for example. The current population of Africa have genomes that show the diversity acquired by all the generations from this long period of time.

    The ancestoral popluations of Europeans left Africa X mya, and so have missed out on on X my of random genetic variation. In addition I believe it theorised that the groups that left Africa were relatively small and few in number, and so all members would have fairly small amounts of variation to start with, effecticely making a genetic bottleneck for non-African popluations. All cheetahs in Africa are closely related, because at some point relatively recently their poplation crashed and have then spread out again from a very limited popluation.

    I always find these sort things easier to conceptualise by considering an extreme example. Easter Island, for instance, was populated by a relatively small number of people realtively recently who had been seperated from the African populations for a considerable time. Consequently there has been neither sufficient time or sufficient numbers for diversity randomly occur.
    Wibble
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