5 continents?

Let's start with "race is a social construct".  The human genome both denies and confirms this.  Are there any differences between people of different races at a genetic level?  Yes!  Are the differences within a race much more diverse than between races?  Yes!

Things to remember. Race is not species.

Biology definition of species; the major subdivision of a genus or subgenus, regarded as the basic category of biological classification, composed of related individuals that resemble one another, are able to breed among themselves, but are not able to breed with members of another species. (for pure curiosity, look at a comparison of chromosome counts  http://en.wikipedia.org/wiki/List_of_organisms_by_chromosome_count http://en.wikipedia.org/wiki/List_of_organisms_by_chromosome_count

Obviously from this chart, having the same number of chromosomes does not make it possible to reproduce.  Hybrids are infertile, with exceptions of domestics from wild counterparts--perhaps these particular species are also a  social construct.

So what is with the continents?  Continents explain our races.  (Antartica??? who knows--if humans ever lived there, they also died there.)   Specifically, geographic isolation over a long  period of time explains races.  And yes, I know that there are more than 5 continents.  At one time (an ice age), the mountains separating two groups of people were as effective as an ocean in separating people.  

Think geologic time.  There is evidence that humans have been around 190,000 years.  The last Ice Age was from 110,000 to 12,000 years ago.  That is not a "some time in there" time frame, but 102,000 thousand year time frame.  History, the part we know via pictures and written word is about 6,000 years.  That means the Ice Age was over for about 6,000 years before we recorded anything that made it to now.  During our "modern, 6,000 years, we traveled pretty well.  We find evidence of ships and artifacts from one place in very unexpected other places.  Just plain determination and teamwork was not as efficient as mechanics and electronics, but effective none the less.

The Ice Age made our current Midwest winters look pretty mild.  People weren't traveling very fast or very far.  And it is likely, that teen pregnancy was more the rule than the exception during that 100,000 plus period of time, so a generation was more like 15 years than 20.   That means over 6,000 generations passed with most people choosing mates from people that lived nearby..  That makes for a small gene pool, not as small as the cheetah gene pool--which will likely be the cause of their eventual extinction--but small enough to create some definite family resemblances. A combination of natural selection for those traits that make surviving in a freezing place versus surviving in a sunny, warm place alter who is more likely to survive long enough to reproduce. Never underestimate the importance of Vitamin D in reproduction.  Add to that humanities tendency to characterize people as beautiful or ugly, desirable or untouchable and you have altered the gene pool again.  A people that values hair color over intelligence, a society that likes short over tall, fat over thin, light over dark, all those things will create changes in the population of that location.  And soon, after only 10 or 20 millennium,  you have something we call race.

If you look at the people living in borderlands, places where the continents connected during that 6-12 thousand year period after the Ice Age (and yes, I am aware that the last Ice age is still sort of slowly melting away as proven by our glaciers still being present in places they weren't during the age of the dinosaurs, but I don't know that we humans really want to speed that up too much, we aren't prepared for the world the dinosaurs loved,  we didn't genetically develop for it.  If it is slow enough, we will, or at least we might survive it.) you will note that they have certain similarities, although those similarities involve a greater diversity than those people living in the areas more isolated.  We see a preponderance of dominant gene phenomes with enough recessive phenomes appearing to make it obvious we are a heterogenous group. In areas without genetic isolation, people rapidly become more diverse in appearance and in genome.  In places that have maintained their gene pool isolation, either by geography or by culture, you develop what racists frequently refer to as racial purity.  A population homogenous in genome and displaying whatever recessive genes they consider to be superior--such as those all blond haired, ice-blue eyed children--no wait, that was the "Village of the damned".  Just kidding, but the Nazi's knew what I was talking about.

But I'm sick of social constructs, thus the 5 continents.  Five geographically isolated-mostly-land masses is all we have.  Therefore, 5 continents:  Africa, Australia, America, and Eurasia.and Antartica (because it is an isolated landmass and may one day prove to be our salvation from ourselves.  If you think I have cheated anyone of there own continent, check a map, or better, an accurate globe.

And while we are eliminating social constructs, maybe we should make race and species synonymous--and leave it at human.