OK, let's get this over with. We need to lance this boil before it festers.
First off, what do we mean by the word 'race'? Well, it doesn't mean what you think - or rather, it has been used to mean so many things in so many different context that it can mean almost anything, which pretty much makes it mean, well, nothing, at least not without some sort of context.
So, what definition do we use? If we are discussing genetics, then the only meaningful definition is to equate it with 'sub-species', but that term is a pretty nebulous one itself - and strictly speaking, doesn't apply to humans at all, as the most consistent definition, "a sub-group of a species with a discernible morphological phenotype which is genotypically distinct from another sub-group but which retains the ability to interbreed in a stable fashion", fails as there are no significant morphological differences of this type in humans - while there are minor variations in morphology (the presence or absence of an epicanthic fold, for example), there is more genetic variation within the groups which possess them than between the groups that do and do not have them, rendering it useful only as a genetic marker, not a sub-species differentiation.
Why? Because, according to the genetic evidence developed over the past twenty years, all modern humans are descended from a single Great Rift Valley tribe that were the sole survivors of a genetic bottleneck some 70,000 years ago. The cause of the bottleneck is speculated to be the eruption of the Toba supervolcano that occurred at the same time, but whatever the cause, the worldwide hominid population dropped from about 400,000 in 75000 BC to an estimated 2500, of whom 1500 were H. sapiens (a relatively minor species at the time, though well established across Africa and Eurasia) living in a single group of families in the allopatric range (the Great Rift Valley in Africa, which is where all but three known hominid species are thought to have evolved - the only possible hominin species thought to have arisen elsewhere, H. floriensis, is of questionable status as a separate species), and all the remaining populations non-hominins - 'hominin' being the species in the genus Homo, as opposed to related Hominid species of other genus such as the australopithicines - went extinct.
All modern hominins have mitochondrial DNA which, if we check the rate of gene drift (random mutations in non-expressed genes, of which the nuclear DNA has a great abundance and even mitochondrial DNA has a detectable amount), appear to have common female ancestor from that 70000 YA period. If we take a very conservative figure of 20 years per generation (the usual figure is given as 25-30), this gives us a maximal interbreeding distance of approximately 3500 generations. It is unlikely that this figure actually applied to any pair of humans anywhere on the planet, not just because the generation time figure is so low, but also because most groups have interbred heavily unless they were geographically isolated - in other words, the only ones who come close to that are the Afro-Australasian and Polynesian groups in in Australia and the southern Pacific islands, who were separated from regular contact for about 50000 years (and even then there was some contact, even if European explorers of the 18th century were unaware of it).
By 50000 YA, H. sapiens was on an upswing, having edged out one of the two other surviving hominins (H. hiedelbergensis) and spreading to every continent except North America and Antarctica (though the group that colonized South America is today only represented by a relict population on Tierra del Feugo, having been overrun and assimilated by the Amerindian group about 15000 YA).
Now, evolution is a continuous process but not a smoothly developing one; for significant changes to occur, there have to be significant adaptational pressures. However, the human brain - which has no significant genetic variation across different groups, modulo some genetic diseases which are found in different proportions in all groups - tends to adapt far faster than the human body, so technology was already replacing evolutionary change even at the time the hominins split from the other hominids 2.5 MYA. This means that most of the differences we see are either adaptations to local extremes, or else expressions of gene drift.
The only significant adaptation, one which is a minor change in expression, is skin color. This adaptation appears to have occurred exactly once, in central Asia, probably around 20000 BC or so during the last major glacial period, and was due solely to the fact that at those latitudes, during the ice ages, the groups in that area had to keep their skin covered most of the year, reducing exposure to UV and lowering the production of vitamin D. In other words, white people (including East Asians and Amerinds, who seem to have split from Caucasians after this happened) are white because of clothing.
The rest? Epicanthic folds are arguable, but things like straight, wavy or curly hair, eye and hair color, and the rest of those 'racial characteristics', are pure gene drift. They changed not because they were significant, but because they weren't, so small inbred groups could become dominated by some otherwise rare recessives that only expressed themselves infrequently elsewhere (which is shown by the existence of blue and green eyes in ethnic Africans and Afro-australasians, something that occurs rarely but is not unknown - the genes already existed when the Eurasian groups split from them, but were almost never expressed because they were recessives in a multi-gene complex).
As for more finely dividing groups, well, all the 'Caucasian' ethnic groups - Celts, Latins, Dorians, Germanics, Semites, Aryans (which refers to Persians, Afghans, and northern Indians, BTW, not Germans), Turko-Ugarics, and ironically enough in light of classical race categorization, Mongols - only left their allopatric range of central Asia (roughly from the Himalayas to modern Mongolia, and including modern Afghanistan, Uzbekistan and Kazakhstan) about 12,000 YA, and were never very genetically diverse compared to Africans (85% of all genetic diversity in humans is found only in the Great Rift Valley even today).
In other words, Muazzam, you are of the exact same race as me, Brendan, and Solar, despite the geographical distances, cultural differences and variety in appearances - there is likely to be less genetic difference between the four of us than between four different Kenyans from the same city. Satisfied?
Finally, regarding intelligence, as I said, human brains are pretty uniform across the species - most of the variation in apparent intellectual capacity is environmental and developmental, not genetic. In any case, we can't even really define what 'intelligence' means in a consistent manner - things like IQ tests have long since been abandoned by psychologists and anthropologists (though sadly, not school administrators) as measuring only the ability to take that particular test, and don't reflect anything that is useful in the real world. Even if we did, it has little bearing on things like performance in a given field, which is more a matter of individual psychology than anything else (e.g., the difference between, say, me and Brendan is mostly due to me being older than Brendan, on the one hand, and suffering from life-long depression, on the other), with some cultural factors mixed in. Genetics is the least significant part of 'intelligence'.
Rev. First Speaker Schol-R-LEA;2 LCF ELF JAM POEE KoR KCO PPWMTF
μή εἶναι βασιλικήν ἀτραπόν ἐπί γεωμετρίαν
Lisp programmers tend to seem very odd to outsiders, just like anyone else who has had a religious experience they can't quite explain to others.
Last edited by Schol-R-LEA on Mon Oct 31, 2016 8:38 am, edited 10 times in total.