So then explain to me how nationalities are so clearly defined. Meaning Irish in Ireland, Italians in Italy etc. Even being geographically close these people are easily distinct in appearance and for that matter as are British in U.K.
It's an interesting facet of zoology that within some species there is very little differentiation in appearance due to genetics whereas in others the difference is riotous. There are some extremely inbred populations of mountain lions in the U.S. but we can't tell them apart. On the other hand, I've read that if you handed someone who was not a primatologist the skulls from two gorillas from different tribes 500 miles apart, they are so strikingly different that he would swear they are two different species. (There are 2 species of gorillas but they're talking about within one species.) Humans, fairly close relatives of gorillas, seem to have the same trait. We have genes that affect our appearance in a wide variety of ways. Since, aside from the obvious function of melanin as a sunblock, it's hard to think of an evolutionary advantage to these utterly ephemeral differences, it's probably just an accident of evolution that we got stuck with physical differences that cause us to hate each other while mountain lions, who are not social animals and couldn't care less, didn't.
Especially the more distinct Chinese (asian) in China and the variations throughout Asia, African (black) in Africa, Scandinavia (white).
Yes, and the Asians wonder why we got such a chaotic range in appearances while they didn't. My Asian friends agree that they look more like each other than we do.
These people would have had to identified themselves early on and migrated in packs...
Well it was the Mesolithic era so of course they migrated in packs. That's how humans lived in those days, in extended families of hunter-gatherers who migrated seasonally to follow wild game and harvest fruits, nuts and herbs. From what I've read I'd say a typical clan size was about 50 people.
...without any interbreeding along the way.
Interbreeding with whom??? They were the first ones there. All we know about the behavior of Stone Age people is what little we can study from the very few tribes still in existence in places like the Amazon and New Guinea, all of whom have been to some extent "contaminated" by contact with nearby civilizations. It's presumed that hunter-gatherer clans regarded each other warily because none could condone competition for food on its own territory. That related tribes may have gathered at festivals during the opulent season when they had nothing to fear from each other. That Homo sapiens's strong urge for outbreeding was practiced at these festivals. (Most of us still find foreigners and people of other "races" sexually exotic and have to be browbeaten by our priests and politicians not to date them.) So, speculatively, there was just enough stirring of the gene pool to keep inbreeding from creating health problems, but not enough to prevent local groups from developing common features in their appearance.
Competition between tribes would have been less of a problem on the leading edge of the diaspora where everyone was staring into an unpopulated wilderness, but the tribes there would not be in close enough proximity to foster outbreeding. Those populations in fact might very well have been the most isolated and inbred ones, and taken their genetically reinforced peculiar appearance to their new home with them.
At what point in history did human differences become defined?
Which differences? As I've noted in other threads, the epicanthic eye fold we regard as the defining component of "Oriental" appearance did not arise until around six thousand years ago, because the "Orientals" who came over to become the first and second waves of aboriginal Americans don't have them. (I don't know if the Eskimo-Aleuts have them, I've never met one. Their migration only goes back 4,000 years.) As I've also pointed out, skin color, another trait that many of us find to be of overwhelming importance, is so ephemeral as to be ridiculous. Populations that move north change from dark to light in less than two thousand years, and vice versa. (Compare the Bengali to their close kin, the Ukrainians.) The skin color of any group of people you pick may have changed ten or twenty times during its migrations.
Any particular physical trait you single out, such as hair color, nose shape, etc., was probably stabilized at a different point in a people's history. Nobody's complete appearance changed and became what we see today as a single process.
When did human populations become segmented and how were the numerous variations established? Not in culture but appearance.
This has been a gradual, iterative process which, at least outside of Africa, has been going on continuously for 70,000 years. If you went back 20,000 years and looked at samples of the ethnic groups that lived on the planet in those days, when Homo sapiens was just setting foot in Europe but had not yet reached the Americas, you would probably not recognize anybody. Prolific tribes who spawned some of the ethnic groups which are culturally dominant today, such as the Arabs and the Indo-Iranian peoples, did not yet exist.
In essence humans segregated themselves?
We didn't "segregate" ourselves. We migrated off in different directions and
separated ourselves physically. That's quite a different verb. Genetic drift created the differences from that point.
From Africa some went east, some went west etc. and some stayed there.
Don't lose track of the fact that this was the Mesolithic era and the nomadic groups you're talking about probably numbered less than a hundred people each. Human life was not as we know it today. People did not live in large permanent settlements where they had to learn to get along with people they didn't know very well. They stuck with their families.
Do you think these founder groups were established before they left Africa and if not how did they develop because if the were not defined before they left then genetically they could have possessed many different variations.
Considering that it took Mesolithic human tribes tens of thousands of years before any of them finally managed to succesfully migrate out of Africa, it was probably not a large number of groups who actually did it. The people who lived south and west of the Red Sea would have had to walk across the territories of dozens, hundreds of unfriendly tribes to get to the Red Sea. Not likely in the Mesolithic. The genetic variation we see in humans outside of Africa surely developed after their ancestors left Africa.
I know about dominant and recessive genes, but do you see the slightest problem here?
I guess not. I don't understand your question. 70,000 years is a long time for genetic drift to redesign a species. Humans used to reach puberty at a much younger age than today, so that's five or six thousand generations!
