Human evolution and differentiation of races

How would differences in height have been selected for, or was that due to diet or baby diet or something?
 
jasonpatterson said:
Folate, I believe. The selective pressure is fairly strong for light skin at high latitudes (avoid vitamin D deficiency) and dark skin at low (avoid neural tube defects in fetuses,) so it happens quickly. As was mentioned earlier, the genetic variation was probably already present in the population. It's fairly clear that Africa is where humanity came from just based on the variety of genetic material there as compared to the rest of the world, not to mention fossil records, etc.
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Thanks!! Folate it is!!:)
 
Dragoonster said:
How would differences in height have been selected for, or was that due to diet or baby diet or something?
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diet, altitude (atmospheric pressure), potentially food sources in some areas(unlikely, but possible), level of pay for athletic skills(:D:D:D:D - unless you add in genetic engineering!)
 
parky76 said:
im no biologist, but I do know that the eye color, hair color, hair texture, and skin color, make up a miniscule amount of our genetic blue-print. let alone the fact that humans, no matter where they come from, can all interbreed.

we are all one species..and our racial differences are purely skin deep.

though, this does lead me to this question:

how long would human groups have to be separated to become separate species?
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Don't know the answer to your question of "how long" but I'd be fairly sure there is no definite answer, it would depend on selection pressures and random chance.

But I would point out that not all humans can interbreed with equal success. There are issues like rH factor which present obstacles to certain pairs of humans breeding even though they would have no problems breeding with other humans.
 
Gawdzilla said:
This requires we ignore the spectrum of characteristics with other "races" and the overlap between "races" that show that "race" is, at the end of the day, just a social fiction and not a biological reality.
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kedo1981 said:
Yes the idea of race is a concept belonging in the dustbin of time.
Science and only science has proven the truth of that.
Let WOO WOOs say we have no wonder in our “souls” but what more exhilarating a notion than all people are one race(and to prove it).
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I have trouble understanding what people mean when they say that "race" is not biologically based, or not a scientific concept, or similar things.

I understand the feel-good, politically-correct idea behind it--that people of all "races" are so similar that there's no point in using "race" to classify people in groups that can then be exploited, denied rights, hated, etc. etc. Obviously, I agree with that.

But it seems we're taking it so far that one can't even state the obvious any more, for fear of being labelled a racist.

Clearly, there are clusters of inherited characteristics among human beings that result in easily visible, consistent differences, when similar people mate. If dissimilar people mate, the characteristics are mixed and matched, so of course it's all very fluid.

But there must be a scientifically acceptable name for this. Not "sub-species," of course. What's lower down than that? "Varieties" perhaps?

Garden vegetables have varieties based on color, size, flavor, etc., but they interbreed and lose their unique characteristics if allowed to mix. Yet still, we understand that Kentucky Wonder beans are genetically different from Black Turtle beans and will breed true, even though they're both the same species. Fortunes are made by seed companies, exploiting these (incredibly) minor differences, producing open-pollenated varieties that are just a little tiny bit softer, harder, sweeter, tougher, faster-maturing, more-disease-resitant, or whatever, than the competition's variety. (I won't go into F1 hybrids or things that must be cloned like roses or apples--but there are plenty of open-pollenated garden plants that this really does apply to.)

So why is it not a scientifically valid truth that similar "varieties" of human beings have developed, due to breeding in isolation, and can be named, and individuals can be more or less similar to their distinct types as they begin to cross with other varieties?

Sure, in a few thousand years, any of those varieties may be "lost" if they're cross-bred, just as older seed varieties get "lost" if people don't carefully isolate them. By then we may have new races of Martians and Earthians, if humans are separated by planets rather than continents and new clusters of characteristics begin breeding true.

But why aren't "varieties" or "races" (for lack of a better word) a scientifically valid concept when applied to humans, if they're valid when applied to other creatures which reproduce and pass along genetic characteristics?

Please note that I did manage to avoid the obvious "human bean" pun. ;)
 
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Pup said:
I have trouble understanding what people mean when they say that "race" is not biologically based, or not a scientific concept, or similar things[....]
Clearly, there are clusters of inherited characteristics among human beings that result in easily visible, consistent differences, when similar people mate. If dissimilar people mate, the characteristics are mixed and matched, so of course it's all very fluid.
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Yes, there are clusters of inherited characteristics and science doesn't deny that. What science has observed though is that there are multiple clusters of inherited characteristics and they overlap in many ways. The problem isn't that race can't be definied scientifically, the problem is that there are many ways to define race and no objective means for saying which one is "the right one".
 
there is nothing "feel good; warm and fuzzy" about it, science proved there is no meaningful
concept of race.
 
parky76 said:
im no biologist, but I do know that the eye color, hair color, hair texture, and skin color, make up a miniscule amount of our genetic blue-print. let alone the fact that humans, no matter where they come from, can all interbreed.

we are all one species..and our racial differences are purely skin deep.

though, this does lead me to this question:

how long would human groups have to be separated to become separate species?
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I recently asked essentially the same question: http://www.internationalskeptics.com/forums/showthread.php?t=162288

The upshot was that a new species is formed when there are two populations of a former species that do not interbreed. Notice that that doesn't say they cannot interbreed - they just don't. The reason could be physical - an incompatibility in chromosome count or a major mutation that makes a given chromosome incompatible, or it might be because one group has acquired a different "smell" from the other and the males are too picky to mate with the wrong smell, or perhaps geographical when they inhabit opposite sides of an impassible mountain range. This definition will separate the Chihuahua from the Great Dane, and so is not fool-proof, but left to their own, they would not interbreed and so genetic drift will eventually make of them separate species. Since speciation is a man-made distinction and not something that nature worries about, the exact point where it occurs will always be somewhat fuzzy.

The edges are: a species is one when the members freely interbreed in the natural world.
Species are separate when even artificial means of breeding between them fail.
In between is a gray area where scientific debate occurs and philosophies collide.

How long? A while, and that's about all that can be said.
 
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RecoveringYuppy said:
Yes, there are clusters of inherited characteristics and science doesn't deny that. What science has observed though is that there are multiple clusters of inherited characteristics and they overlap in many ways. The problem isn't that race can't be definied scientifically, the problem is that there are many ways to define race and no objective means for saying which one is "the right one".
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I believe Pup is making a valid observation. There is a bit of "political correctness" in play here.
Olive producing trees are all one species but we have no trouble talking about mission olives, kalamata olives, manzanilla olives, etc. (there are dozens). They have distinct characteristics and are quite easily identified. I cannot imagine that olives cannot be identified scientifically any more or less than human races (or if you prefer -- varieties) can be identified. Put a garden variety Swede next to a native Australian: How much trouble would you really have defining the differences?
 
Perpetual Student said:
I believe Pup is making a valid observation. There is a bit of "political correctness" in play here.
Olive producing trees are all one species but we have no trouble talking about mission olives, kalamata olives, manzanilla olives, etc. (there are dozens). They have distinct characteristics and are quite easily identified. I cannot imagine that olives cannot be identified scientifically any more or less than human races (or if you prefer -- varieties) can be identified. Put a garden variety Swede next to a native Australian: How much trouble would you really have defining the differences?
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Did you misread my post? I didn't say that human races can't be identified. I said the opposite. Human races can be identified and in multiple ways.
 
kedo1981 said:
there is nothing "feel good; warm and fuzzy" about it, science proved there is no meaningful
concept of race.
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Not true:

LINK

'According to forensic anthropologist George W. Gill, blanket "race denial" not only contradicts biological evidence, but may stem from "politically motivated censorship" in the belief that "race promotes racism."'
 
Lessee now, we know about approximately seven different genes for skin color. So, obviously, there are scientific differences (the scientific field is called "Genetics").

I think sub-species is the lowest taxonomic level. We are mostly of the species 'homo sapien', aren't we? Which could then be divided into sub-species?

Of course sub-species are many, in many combinations. Looks to me that any discernable genetic difference could be a distinct sub-species.

Perhaps we ought to start a list of sub-specific differences?
They would have to genetic:

Skin color
Hair color
Hair texture
Nose width
Forehead precession
Eyelid shape
Iris pigmentation
Muscle fiber variations
Disease resistance (or the lack), many many of them
Blood types
Fat storage locations
Height

Hmm, I don't think IQ is a valid difference, there is so much overlap, with only one standard deviation between sub-species.

So, I guess by 'race' people mean 'sub-species'?
 
casebro said:
I think sub-species is the lowest taxonomic level. We are mostly of the species 'homo sapien', aren't we? Which could then be divided into sub-species?
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All humans now are Homo sapiens sapiens. We're all already classified as a subspecies of Homo sapiens.
 
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casebro said:
So, I guess by 'race' people mean 'sub-species'?
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I assume they mean "breed". Which is fine to use scientifically, just not in taxonomy I guess. But "black" and "white" and "pacific islander" can be used in genetics or demography or sociology and so on. Saying it can't seems a Loki's Wager fallacy, and hypocritical considering the same practice exists in other science such as medicine. Consistent people against the use of race in science should also want medicine to stop using "foot" and "ankle" since they aren't discrete units either.
 
wait...so Homo sapiens could breed with all the other Homos?

like Homo aferensis and Homo neanderthalensis?

cool.
 
It's doubtful we could breed with all other human species, but is' currently an open question. It appears we didn't breed with out closest known relative neanderthalensis, but it's not known why didn't. Maybe we could have if we tried.
 
A classic example of thinking you have a race difference and then finding out otherwise is Gaucher's disease and other lipid storage diseases. When Genzyme began working on a drug for this disease, it was an Ashkenazi Jew disease. Surprise! Now it's also Swedish, Spanish, Japanese, and others. In particular, Type 2 Gaucher's occurs across many ethnicities.

Just when you think you've got the race thing figured out, it gets more complicated.

~~ Paul
 
Roboramma said:
I'd like to echo what Athon said above, and also point out that a great deal of the variation may have already been present: ie. new mutations may not have been necessary (or at least, not very many) to create the apparent differences.

Instead, variation that was already present might simply have been selected on. That is, for instance, certain genes could have been selected out rather than new ones selected in. Get rid of a melanin producing gene, for instance, and you've got whiter skin without needing new variation to arise through mutation. The mutations could have taken place in the past. That's what's great about a large, diverse gene pool and sexual reproduction: you've got access to a great deal of variation for selection to act on when conditions change took quickly for new mutations to arise.

I think it likely that both selection on old variation and new variation arising through mutation likely had a part to play.

But, as Athon said, the differences between the races are really very small, so it's not surprising that it could arise in a short period of time.
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Quite right. Even the native Australian population has been found to contain, if I remember correctly, 86% of the total genetic diversity of the human species.
 
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