How did the different human races evolve?

Discussion in 'Science & Society' started by Balder1, Jan 26, 2003.

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  1. Facial Valued Senior Member

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    I think we have races because of something I learned in bio called genetic drift. When the first humans re-emerged from Africa they must've split up into pretty small nomadic groups from tribal conflicts or whatever. In small groups, genetic variations happen to drift more and more. So the same species, humans, must have come out of Africa and once they splitted into different groups, they start to drift apart genetically. This is probably how races developed. Before the races could become their own species, however, our intellectual and technological development on globalization grew too fast. Today, the genetic drift has pretty much stopped due to large populations in most races. You can see how modern-day humans have different genetic adaptations, especially in Africa. Africans have more resistance to solar radiation and have heterozygote superiority to sickle-cell anemia. Also, the faces of Native Americans almost became indistinguishable with that of the Asians, indicating that a small group (maybe hundreds or several thousands) migrated across the Bering Strait 12,000 years ago, but still you can see the similarity.
     
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  3. Oxygen One Hissy Kitty Registered Senior Member

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    Even among the white races there are distinct variations. That's why I get a kick out of forms that ask for race and list "White", "African American" and "Native American" as catch-all categories, ignoring the diversity within the groups. I usually check "Other" and put down "Gaelic-Germanic-North African-Anasazi". THAT oughta screw up their database! I wonder how many scholarships I qualify for?

    (My husband is a classic Heinz 57, although his facial features are distinctly Russian.)
     
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  5. Facial Valued Senior Member

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    Very true, oxygen. You qualify for many

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  7. Tracker00 Registered Senior Member

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    race is just a social construct. so people we an extra bone in their foot and people without the bone belong to different races. maybe tall people are one race and short people are another.

     
  8. river-wind Valued Senior Member

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    "Why do you think so many Asians have to wear glasses?"
    the WHO just finished up a study on this and determined that the higher rates of near-sightedness had mostly to due with life-style. As western society shift more and more to spending time inside, focusing on close-up objects (esp during childhood), we will see an increase in near sightedness here as well.

    And Spurious, there is some study into the passage of certain learned-traits in a lamarkian-like way. Given that it looks more and more that the structure and pathways of the protiens already present in the mother's gametes may have an effect on the accuracy of DNA reproduction, the life of the mother will have a very minor effect on the child's basic genetic code. over thousands of generations, given similar environmental pressures, you might see the externalization of that subtle effect.

    Lastly, to the person who said that two populations, separated for a long time would become two species: you are close. Not quite right though. Two populations, unable to cross-breed, have a *chance* to become different species, if there is environmental pressure to drive evolution in two different directions. If you have two populations, place them in two seperate but completely identical environments, there would only be random chance driving the divergence of the populations. Much more than a couple hundred, or even a couple thousand years would most likely be needed to end up with two different species in such a situation. (note: there is a small semantic caviot that any time two populations are seperated, they are considered different species, because they wouldn't encounter eachother naturally anymore; but that's just semantics.)
    The classic example of the Galapagos finches specifically depended on the different food sources on each of the different islands.
     
  9. river-wind Valued Senior Member

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    Genetic drift could account for a certain amount of the differences between groups, but genetic drift specifically only deals with the frequency of traits within a populations.
    If you have a group with 50% x and 50% y, then wait a few years, and find 25% x and 75% y; that is genetic drift.
    If, however, you have a group that is 50% x and 50% y, then test again year later and find 25% x 25% y, and 50% q, that is evolution.
    I would simalarly put a group originally at 50% x, 49% y and 1% q, later found to be 50%x and 50% q in the classification of evolution. Even though no new genetic types were introduced during the testing time frame, the population's genetic pool have been altered; not just shifted within the original choises - genetic option y is gone in this case.

    FWIK, the different human "races" actually do have occurances of differing genetic pools to choose from, suggesting evolution, and not just drift.
     
  10. paulsamuel Registered Senior Member

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    They are right. Given time and genetic drift, speciation will occur.

    that chance is 100%, with drift alone, given enough time: no need for selection.

    It could also be selection.
    Evolution is the change in gene frequency over time (usually measured in generations). Both of the gene frequency scenarios that you presented are examples of evolution. I.e., genetic drift is evolution.

    As Tracker said, human races are social and cultural constructs, not biological taxa.
     
  11. river-wind Valued Senior Member

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    why is that? The more time, the better the chances, but I don't see a 100% chance there. With no environmental pressure, or more accuratly, no difference in environmental pressures, then only the randomness of mutation and meiosis will determine genetic change over generations. There is always a chance that this will not lead to new species.

    It is my understanding that selection will lead fist to genetic drift within a population, then to evolution of that population; I don't see selection as mutually exclusive of drift. Selection is a force which effects Drift and Evolution.
    ok, I see the logic in that definition. I have largely been taught that genetic drift is something sort of apart from evolution, but I guess you are right.

    But there is certainly phenotypical difference between people whose ancestors came from different areas of the world. While genetic variation may be greater within a given population (between individuals within a single 'race') than between 'races', the chances of active combinational gene sets (ie, the chance of a phenotypical item occuring in an individual) is greater within those races.
    I have two caucasean parents. We have Native American blood down the line, but 90% of my ancestry is European. While the diversity between me and a random guy from France may be statistically more (based on total gene difference %) than between me and a guy from SE Asia, phenotypically (and therefore genomically in terms of active gene sets, not just individual genes), the guy from france and I are more alike.
    If genes determine if I am red-haired or brown haired/light skinned or dark skinned, then genes certainly play a role in 'races'. the lines drawn between this race and that race are certain culturally defined; there is no genetic arbitration between one race and another. However, you do not find dark-skinned children born to purely northern european families.

    Would you suggest that different breeds of domestic animals within the same species are simply social constructs? If so, then the entire idea of species could be considered a social construct as well; much of the time there is no hard genetic line between species A and species B, at least by the current definition of species.
    Any sort of classification system will be based on social construct; however, that doesn't preclude that there may be reasoning behind it.
     
  12. paulsamuel Registered Senior Member

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    Originally Posted by paulsamuel
    "Given time and genetic drift, speciation will occur...that chance is 100%, with drift alone, given enough time: no need for selection."
    because the force that keeps a species cohesive is interbreeding, prevent interbreeding and differences will build up steadily until the inevitable reproductive barriers appear. They could be chromosomal, or behavioral. They could be based on cell receptor sites (i.e. those responsible for sperm recognition by egg) or merely mechanical (e.g. chirality in snails or the fitting of pedipalp into seminal vescicle). Drift alone leads to speciation.

    genetic drift is the random differentiation of the genomes of two non-interbreeding populations. selection is, by definition, directional, and therefore, non-random. The 2 are mutually exclusive, but generally act together.

    race is a biological term.

    it was used by natural theologians in the 19th century to explain species variation. God was supposed to have created and placed each species on earth, but it was obvious that phenotypic variation within a species occured in local geographic forms. instead of advocating that God created these variations (which would lead down the slippery slope to advocating that, because each individual of all species is slightly different from one another, God created each individual of every species that ever lived on the face of the earth), it was concluded that these variants occured naturally due to local climatic differences, and these were termed 'races.'

    It is an antiquated term rarely used today and is mostly replaced by the term 'subspecies' or 'sub-species.' The only known sub-species of humans is Neanderthal man (Homo sapiens neanderthalensis, c.f. H.s.sapiens).

    Although no one denies that there is phenotypic variation in humans, and to some extent this variation is geographic, the time of isolation was not enough to differentiate the populations into sub-species.

    Phylogenetic studies have shown this to be the case in humans.

    For example, if you made a family tree of humans, from the beginning of the species to the modern day, you can determine the familial relationships of each human alive today. If you try to map racial characteristics on this family tree (i.e. skin color, hair color, eye shape, etc.), you would have to break the family links to keep the racial characters cohesive. That is, the racial characters don't fall out along family lines, that is they don't fall out along relatedness, that is they don't fall out along genetic similarities.

    yes i would, if they present the same problems as related for humans. i don't know enough about the phylogeny of domesticated animals to know if they fall out along familial lines or not.

    yes, i would not argue with that. what i'm saying is that it's not biological, it's not scientific; it's arbitrary constructed along social and cultural guidelines.
     
  13. Preacher_X Registered Senior Member

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    i heard in a documentary that it takes 20,000 years for a race to go from black to white and vise versa
     
  14. celtic origin Registered Member

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  15. ElectricFetus Sanity going, going, gone Valued Senior Member

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    ya the lack of statically relevant data showing its true.
     
  16. celtic origin Registered Member

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    why do you say that is there any scientific evidence to prove your theory its bs and i don't mean to be a sadist by saying this i just wanted to ask you because you seem to know quite a lot
     
  17. Facial Valued Senior Member

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    I would like to emphasize the population sizes of the ancient nomad groups being small ; that is when genes start to get probabilistic and not empirical.
     
  18. bradguth Banned Banned

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    How about instead of the pure happenstance of random panspermia, and of the hundreds of uninterrupted millions if not billions of years worth of continuing happenstance evolution transpiring, we take an honest look-see at the possibilities of terraforming.

    It is quite clear that our solar system has in the past, and will again in the future cruise sufficiently close to the Sirius star system, perhaps as close as 0.01 light year. In which case all of hell is going to bust lose from the matrix of opposing Kuiper flak, although allowing the capability of others, a whole lot smarter than all of humanity, as to pay us another visit.

    BTW; I'll be glad to offer scientific backing as for supporting this conjecture.

    Of course, if you'd be insisting that your Earth is flat, and thereby we are the absolute sole center of this universe, then God help us because, right about now humanity is running itself seriously amuck, and our messily flat-world isn't going to keep ticking if this godforsaken trend continues.

    Keeping in mind, as unlike a good number of seemingly "all knowing" folks having their free run of this forum, I'm certainly not the one that's excluding upon the possibilities of evolution, of the environment influencing upon whatever, nor even that of creation. I'm just proposing that we are NOT the center of this universe.

    Regards, Brad Guth (BBCI h2g2 U206251) http://guthvenus.tripod.com/update-242.htm
     
    Last edited: Jul 31, 2004
  19. eburacum45 Valued Senior Member

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    There is only a miniscule chance that Sirius has ever come close to the Solar system; I am not discounting it, just pointing out that the relative motions of stars in a galaxy are largely chaotic because of the difficulties in calculating gravity in a many body problem.
    So there is no more reason to say that Sirius has come close to our solar system than any other star.

    And it would be impossible; literally impossible; to prove that Sirius (as opposed to any other star) has ever been that close.

    However; an interesting idea...
     
  20. bradguth Banned Banned

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    Is perchance you're real name Mr. Negative?

    Do you still belong to the "Flat Earth Society"?

    Sorry about that but, I do believe you're dead wrong, as you're discounting a great many folks that seem to know at least a thousand fold more than you or myself.

    "And it would be impossible; literally impossible; to prove that Sirius (as opposed to any other star) has ever been that close."

    Lets just say (speculate if you'd care), that I, or rather diatoms, can prove that none other than Sirius has been as close, enough to have influenced our global environment, and that's upon more than one occasion.
     
    Last edited: Aug 2, 2004
  21. James R Just this guy, you know? Staff Member

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    Ok then. Show me the money!
     
  22. There is only one human race; Homo sapiens sapiens. Read "The Journey of Man: A Genetic Odyssey" by Spencer Wells
    or check these:
    http://www.mnh.si.edu/anthro/humanorigins/ha/sap.htm
    http://www.ncbi.nlm.nih.gov/genome/guide/human/
    http://en.wikipedia.org/wiki/Humans
     
  23. Facial Valued Senior Member

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    There's only one race of domesticated dog: Canis familiaris.
     
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