Human evolution and differentiation of races

Debunker

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One thing I can not understand about human evolution, is how races can have differentiated in such a small amount of time.
According to Wikipedia (sorry, can not post the link yet, it is the page "Human evolution"):

The dominant view among scientists concerning the origin of anatomically modern humans is the "Out of Africa" or recent African origin hypothesis,[4][5][6][7] which argues that H. sapiens arose in Africa and migrated out of the continent around 50-100,000 years ago, replacing populations of H. erectus in Asia and H. neanderthalensis in Europe.

This means that all the current differentiation in skin colour, eye colour and so on, between say, an Irish and a Senegalese, has occurred in about 2000~4000 generations (50000~100000years/25 years average per generation).
Can natural selection operate in such a short number of generations?
 
I think the assumption you're making here is that the phenotypic variation we see between geological populations is somehow fairly huge. Appearances can be deceiving. Look at the dog population, for instance. Selective processes (albeit conducted by conscious selection) have created a massive difference in phenotypes, and yet genetically they aren't as diverse as it would seem. Chihuahua eggs can still be combined with wolfhound sperm to make a dog.

Surprisingly few mutations are required to create significant looking differences. Add to that the fact that our brains are tuned to highlight the differences between 'us' (our population) and 'them' (those from other groups), and the minor variations now look rather impressive.

To answer your question, the seemingly vast differences between a person from Nigeria and a person from Norway rely on relatively simple genetic changes that did indeed occur within in a relatively 'short' amount of time.

Athon
 
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.
 
Debunker said:
One thing I can not understand about human evolution, is how races can have differentiated in such a small amount of time.
According to Wikipedia (sorry, can not post the link yet, it is the page "Human evolution"):

The dominant view among scientists concerning the origin of anatomically modern humans is the "Out of Africa" or recent African origin hypothesis,[4][5][6][7] which argues that H. sapiens arose in Africa and migrated out of the continent around 50-100,000 years ago, replacing populations of H. erectus in Asia and H. neanderthalensis in Europe.

This means that all the current differentiation in skin colour, eye colour and so on, between say, an Irish and a Senegalese, has occurred in about 2000~4000 generations (50000~100000years/25 years average per generation).
Can natural selection operate in such a short number of generations?
Click to expand...
Yes. These differences are very superficial. Modern humans aren't different enough to have any actual subspecies.
 
Roboramma said:
Get rid of a melanin producing gene, for instance, and you've got whiter skin without needing new variation to arise through mutation.
Click to expand...

Or, even easier, just downregulate the gene without losing it.
 
IIRC, moving from pale to deep black requires a move from up North or way down South to around the equator and hangin' in there for about 10,000 years. To switch back, just reverse. and every 10 or 15 degrees away from the equater lightens you sufficiently to notice (or the reverse darkens) after about the same 10,00 years. This is due to Vitamin D and another chemical I usually forget and have now and the sun's effect on same.
 
Also, the selection of human phenotypes might be selected very quickly by cultural means. If just a couple of folks in a population that had migrated a ways north from a parent population happen to get rickets, darker skin might be remembered as "unlucky" in future generations more rapidly than it was actually becoming a detriment to reproduction.

Did that make sense?
 
Also note that 2000~4000 generations (50000~100000years/25 years average per generation,--Debunker's numbers). ain't really a lot of time, genetically, especially when describing the very-few shifts from, say, a common ancestor of both Neanderthal and Modern Human.

The OP tries, but where most Creationists fail in the conception of the time spans of which we speak. 6000 years? Yeah, it seems fishy. Millions and billions of years? Fishy stopped bidding eons before because he had to decide between the scientifically impossible extraordinarily unlikely and what is plainly fantasy.
 
fuelair said:
This is due to Vitamin D and another chemical I usually forget and have now and the sun's effect on same.
Click to expand...

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.
 
fuelair said:
IIRC, moving from pale to deep black requires a move from up North or way down South to around the equator and hangin' in there for about 10,000 years. To switch back, just reverse. and every 10 or 15 degrees away from the equater lightens you sufficiently to notice (or the reverse darkens) after about the same 10,00 years. This is due to Vitamin D and another chemical I usually forget and have now and the sun's effect on same.
Click to expand...

were you thinking of this ?
http://en.wikipedia.org/wiki/SLC24A5
SLC24A5 (solute carrier family 24, member 5) is a gene that is thought to explain between 25 and 38% of skin pigmentation variation between Black African and White European humans.
Research led by cancer geneticist Keith Cheng and anthropologist Mark D. Shriver at Penn State University along with a number of other institutions discovered that the gene has two primary alleles that differ in only one nucleotide, changing the 111th amino acid from alanine to threonine.

The threonine allele was present in 98.7 to 100% among several European samples, while the alanine form was found in 93 to 100% of samples of Africans, East Asians and Indigenous Americans. The variation is a SNP polymorphism rs1426654, which had been previously shown to be second among 3011 tabulated SNPs ranked as ancestry-informative markers. They also showed that SLC24A5 explains between 25 and 38% of the European-African difference in skin melanin index.

It is currently estimated that the threonine allele became predominant amongst Europeans 5,300 to 12,000 years ago
Click to expand...

no white people existed in 10,000bce anywhere on earth, the new source of Vitamin D is believed to have been from fish at first and then later on from milk
;)
its said that the largest genetic variation exhibited between two humans is between west and east Africans
 
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This is what the creationists refer to as "microevolution", and proper people refer to as "adaptation". Carried far enough, this might lead to speciation, but it's by no means certain.
 
I am only lightly read on this subject, but from what I recall with the explosion of genetic studies genetic biologists were surprised at how little variation humans actually have. Something less than single breeds of some cats and dogs. The various adaptive variations in humans are very minor differences. Even within a handful of generations we can witness changes in skin tone, height, build ect among a small group.

It is not uncommon for people to think skin color variation is a major trait differnce, but it is incorrect.
 
arthwollipot said:
This is what the creationists refer to as "microevolution", and proper people refer to as "adaptation". Carried far enough, this might lead to speciation, but it's by no means certain.
Click to expand...

I think I'm a proper person, but I'd use microevolution, as well as adaption. In fact micro- and macoevolution are actual scientific words, though redefined by creationists for their own agenda.
 
"species", in the simplest definition, are creatures who can successfully reproduce with each other. "race" is a construct we've developed to classify "differences" between groups of people. 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.
 
chum said:
Another example: en.wikipedia.org/wiki/Peppered_moth_evolution
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Since the Peppered moths exhibited white, black and mottled/peppered colorations already they're a better example of how a change in the environment will change selection pressures than in the advent of novel characteristics per se.

That said, in case there are any Jonathan Wells fans lurking here - they're probably the best natural experiment for natural selection ever and therefore perfectly good examples of evolution.
 
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).
 
A (very knowledgeable) poster on another forum says that prior to the last OOA, people had dispersed widely over a long period of time into varying types so that when the small group of our species found themselves all back in Africa, all the varied genes were there in one group or another. When they spread out again, the adaptation would have been quicker.

I probably haven't got that right - it's something very difficult to get one's head round - but that's the general gist I think.
 
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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