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Thread: Need help with an evolution question.

  1. #1

    Default Need help with an evolution question.

    Hi Folks,

    I need information on this question and a cursory search of the net is not yielding what I seek.

    Most evolutionary models seem to show man changing from a monkey like animal into a muscular White guy with wavy hair. What I need to understand is the evolutionary pattern for Asian decent Humans. Specifically the origins of the eye shape variations, skin tone and common body structure traits that seem prevalent in sections of the world that are purely Asian decent.

    A student hit me up with it and I had no answer for him, since I am not a Biology major, I have only a basic understanding of the physiological evolution history of our species.

    Please contain responses to informative arguments or statements. Please refrain from persuasive argument on the validity of Evolution VS. Creationism.

    I just need the best theory and ideas on how the deviations in our species occurred and maybe hypothesis as to why.

    Thanks Folks.

  2. #2
    Butterfly Mage

    Default

    I think the "muscular white guy" is just a generalized example. A big factor in skin tone evolution is the intensity of solar radiation in a geographic region. People whose ancestors thrived closer to the equator tended to have darker skin as a survival trait.

  3. #3

    Default

    It's not that a monkey changes into a caucasian man... In the "depiction of evolution" image, the first animal is not a monkey (monkeys are contemporaries of humans), it is the ancestor to both humans and monkeys.

    This pre-modern ape would then have evolved into humans (of African origin, as this is where mankind is believed to have originated). At some point, human populations spread across the world and regional isolation (by continents separated by oceans), and the original African-origin humans would evolve according to local conditions to take on the stereotypical physical features/characteristics of the various regions.

    Does that help? I'm no expert -- this is just my understanding of how it all works!

    ---------- Post added at 13:51 ---------- Previous post was at 13:42 ----------



    Quote Originally Posted by Fragarach View Post
    What I need to understand is the evolutionary pattern for Asian decent Humans. Specifically the origins of the eye shape variations, skin tone and common body structure traits that seem prevalent in sections of the world that are purely Asian decent.
    To answer more specifically, I don't think anyone knows why there is a difference in eye shape between Europeans and Asians. It may be that the eye shape has some peculiar evolutionary advantage for people who originally lived in Asian regions, or it may simply be associated with a gene that has multiple functions.

    I don't know much about genetics, but I've heard that genes don't usually encode single distinct traits. So maybe the genes that control eye shape are the same ones that cause a boost in immunity from illness. So in this (completely made up) example, the eye shape could be correlated with improved health (although the eye shape does not cause the health benefits, or vice versa).

    As I say, I don't actually know much about genetics, so maybe someone with some expert knowledge would be able to polish this theory into something scientifically plausible... I don't know!

  4. #4

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    I'm a biologist and what Tiny said is 100% accurate.

    I think the biggest reason why those models tend to show a white male is because it is the least controversial. If you used a black male given historical racial slurs that compared blacks to monkeys it would become controversial for that reason. Given Americans have made racial slurs about other races as well a white male is the safest thing to use.

  5. #5

    Default



    Quote Originally Posted by Fragarach View Post
    I just need the best theory and ideas on how the deviations in our species occurred and maybe hypothesis as to why.
    while some differences are obviously due to environmental adaptation, others can only best be described as coincidental.
    the 'slanty' eyes, as usually typified in asians, is probably one of those coincidences - a simple matter of a related group travelling together at a particular time and taking a family trait with them. that's not to say that slanty eyes are solely asiatic, though, as many negroids also have such features (and discounting interbreeding, with that).
    as with a lot of racial features, isolation tends to magnify the differences.

    current views on wikipedia: http://en.wikipedia.org/wiki/Recent_..._modern_humans
    also, a good series of tv progs by the delicious Dr. Alice Roberts: http://www.mytvblog.org/?p=4429
    i think the final episode deals with the asian thing, with some interesting chinese views on race; can't remember for sure, though.

    [edit] no, it's the second episode, not the final.
    Last edited by ade; 06-May-2012 at 21:37.

  6. #6

    Default

    All excellent answers, I wish we had a "Thank you" Button, like I see on other forums. Let me say a general thank you and put an extension question to the group.

    To the best of our knowledge or at least the best educated projection science can make. Did Human evolution begin while the earth's land masses were still contiguous in what was once called "Pangea"? I have seen mention of "Mitochondrial Eve" at about 160K years ago but I also see people state the roots of Human life as far back 2 to 4 million years and some as far out 300 million years ago.

    Is M-Eve still the oldest specimen of Human life?

  7. #7

    Default

    Pangea was a long time ago, back when the dinosaurs trotted around. The only mammals that existed back then were rodent-sized.

  8. #8

    Default



    Quote Originally Posted by Fragarach View Post
    To the best of our knowledge or at least the best educated projection science can make. Did Human evolution begin while the earth's land masses were still contiguous in what was once called "Pangea"?
    It wouldn't have been Pangaea as that rifted around 200 million years ago but the continents would have been closer than they are now and there would have been land bridges from Africa to Europe and Asia at some point and I think Asia to North America but Australia was detached by this point. Also is thought that we left in waves rather than one group left and spread out from there.

  9. #9

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    How did the scientific community determine the timeline? Carbon Dating? or some other form of deep history/event, linear sequencing model?

    I'm sorry I am asking so many questions about this. With graduation and Finals, I don't have a lot of time to focus on reading any books or research papers that are not directly connected to the end of semester work. I want ti give an honest answer and if that honest answer is "I don't know" I am fine with that, I just don't want to say "i don't know" without at least checking into it a bit first.

  10. #10

    Default



    Quote Originally Posted by Fragarach View Post
    Most evolutionary models seem to show man changing from a monkey like animal into a muscular White guy with wavy hair. What I need to understand is the evolutionary pattern for Asian decent Humans. Specifically the origins of the eye shape variations, skin tone and common body structure traits that seem prevalent in sections of the world that are purely Asian decent.

    [. . .]

    I just need the best theory and ideas on how the deviations in our species occurred and maybe hypothesis as to why.
    This question is, to an extent, misguided. You're missing a fundamental premise of evolution: it isn't purpose driven. To an extent, this is understandable. It seems entirely plausible to think of evolution of purpose-driven when we talk about adaptation. But viewing it as adaptation is very cart-before-the-horse.

    I'll also admit that scientists are often too loose with the word evolution in this regard. Its use is sometimes to refer to the process of new traits appearing, which is almost more or less random chance. However, we also use it to refer to the process of environmental selection (the environment weeding out unfit phenotypes), which is not random. So it's important to scrutinize exactly what a scientist or student is using the word evolution to refer to.

    Purpose-driven evolution was an idea strongly pushed by Lamarck (and is often referred to as "Lamarckism"). His common example is the giraffe. This is an extreme oversimplification, but you can think of a giraffe as essentially being an evolved form of a horse- if you think about it, a giraffe does rather resemble a massive horse with a long neck and a funky coat. Anyway, Lamarck posited that there was an open niche for an animal that could eat leaves high on trees, so horses evolved into this niche.

    As I said, this is a cart-before-the-horse case. Let's turn it around the right way. Evolution leads to the random appearance of new traits. The vast majority are deleterious or neutral. Once in a rare while, one appears that makes an individual more fit. Genetic variation in a population of horses, through various direct and indirect mechanisms, results in some horses having longer necks. Horses in the 99th percentile for neck length can reach leaves others can't, feed better, and survive more often. Rinse and repeat for tens of thousands of years and you get giraffes. This is called directional selection, when individuals at one extreme end of a non-binary characteristic are selected.

    So let's apply this concept to human evolution, like you mentioned. In some cases, evolution does actually result in selection by the environment: people with darker skin (entirely a genetic quality) are more suited to survive at equatorial latitudes: as such, people whose genes lead them to have darker skin are selected by the environment for survival. But the fallacy your student (friend?) fell for is that sometimes, a trait evolves which is neither positive or negative with regard to fitness. Livescience recently had an article about this with blue eyes; some recent science suggests that there was a single mutation event in human history that produced blue eyes, and that all people with blue eyes can be traced back to a single Eve. Eve is a term we use to mean a single person whose progeny include people of a certain group. Sometimes a characteristic appears randomly and is just spread by random chance- it doesn't become ubiquitous like dark skin in Africa because it doesn't improve fitness, but it isn't deleterious so it doesn't disappear. Again, blue eyes are a great example.

    This is where evolution in a ends in a biological sense and starts in a psychological sense. People tend to ingroup. When you're looking for a sexual partner, you look for people who resemble you. The basic idea is that this prevents outbreeding depression (too much genetic distance can be as dangerous as too little). However, this also leads to the formation of races. When you put 10,000 people in a room and tell them to fuck, when they seek out people who look like themselves, you'll get in-grouping as people fuck people who resemble themselves. Keep this trend going, and you can imagine that you get distinct looking groups when tall people seek out tall people, when people with this eye-shape seek out people with the same eye-shape, when people with fair-skin seek out people with fair skin. If you continue this for hundreds of thousands of years, as genetic mutations spring up and propogate through individual groups without being passed to the other groups, you'll even see speciation.

    In other words, the fact that Asians tend to have eyes with this shape is likely one of two reasons:

    1. This eye shape randomly appeared in the ancestral population, served some unknown advantage to survival, and was passed on.
    2. This eye shape randomly appeared in the ancestral population, neither helped nor harmed survival, and was passed on in great numbers due to simple chance.


    ---------- Post added at 06:26 ---------- Previous post was at 04:32 ----------



    Quote Originally Posted by Fragarach View Post
    How did the scientific community determine the timeline? Carbon Dating? or some other form of deep history/event, linear sequencing model?
    A combination of radioisotope dating and stratigraphy. Radioisotope dating tells you age. Stratigraphy helps you match up bedrock layers X/Y/Z in South America with the same bedrock layers in Africa. Wikipedia has fantastic pages about both.

    Carbon dating only works for biotic material, and only has a window of about 50,000 years (IIRC). After 50,000 years, both carbon isotopes stop breaking down and their concentrations (and thus, the ratio of their concentrations, which is what we're concerned with) will remain static. Therefore, carbon dating will yield the same results for 100,000 and 200,000 year old bones. If you're looking at material that formed 100 million years ago, you use radioisotopes that take hundreds of millions of years to break down rather than ones that break down in 50,000 years. Or in the case of dinosaur bones, you can also use radioisotope dating to date the rock you chisel them out of.
    Last edited by AEsahaettr; 07-May-2012 at 11:53.

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