I'll try to bring some scientific arguments in this racist ?debate?
Children are not racist. Human beings in isolation are not racist. On the contrary, humans have an innate tendency to marry outside their immediate group.
Racism is learned, and a social thing: always the result of some part of a population fighting against another part for resources, jobs, power, whatever. Skin color and other superficial traits are just an easy way to define who is "us" and who is "them", especially if the two groups came from different parts of the world. But when those markers won't work, some other marker can be used -- language, religion, pedigree, etc.. Skin color only became significant in Europe when European countries established colonies abroad, and had to separate themselves from the natives to prevent them from infiltrating their local administration and weakening their control. In the Americas, physical appearance was instrumental to oppress the natives first, the African slaves later. Skin color worked in the US initially, but when races started to mix, the "whites" had to invent the "one drop rule", based on pedigree, to preserve the "black"/"white" dichotomy. Hair and eye color are as conspicuous as skin color, but were never used as "racial" markers in historical Europe, for the obvious reason. Religion, even just the brand of Christianity, served for the purpose in Europe for centuries after the Protestant revolt, and is still used in Northern Ireland, Palestine, Bosnia x Serbia, Hindus x Muslims, and many other places. I have been told (don't know if seriously) that the only distinctive marker that Serbians and Croatians could find was the alphabet used to write their language. In India, the caste system seems to be maintained mostly by pedigree; that is also how the Japanese separate themselves from the pariah who do "impure" jobs, and from the "Koreans" who have been living in Japan for generations.
"Race" is not a biologically meaningful concept. Racists hate modern genetics, because it thoroughly trashes the axioms that they built their worldview and their lives upon. Humans are exceedingly mobile and promiscuous, and genetically varied. Skin color is a trait that evolves quickly in response to the environment; the light-skinned American natives in Patagonia probably descended from dark-skinned Peruvian natives who descended from light-skinned Siberians who descended from dark-skined Africans. Under the skin, there is much more diffrerence between individuals of the same race than between the "average" individuals of two different races. (I recall a marathon in an Olimpiad, many years ago, when the first three places were an Italian, a Japanese, and a Kenyan -- who crossed the line within a few meters of each other, after a 40'000 meter run. That means, less than 0.1% difference in their running speeds. So it seems that race is a totally negligible factor in races, at least.
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If one rounds the average time between generations to 30 years, a person living today had about two ancestors of the same age living 30 years ago, four living 60 years ago, and so on. 600 years ago --- that is, 20 generations ago -- the count would be 2
20, which is about one million. While Caesar was having fun in bed with Cleopatra, some 2000 years ago, each person alive today had about 2
66 slots on his genealogical tree. So, in order to ensure one's purity of blood, one has only to verify that none of those 73'786'976'294'838'206'464 ancestors, give or take a few quintillion, was African, Jew, Latino, Pariah, Hindu, Mongol, Samaritan, or whatever other "inferior race" is in one's book.
Of course, most of those potential ancestors were the same person; that is to say, the ancestry of one person may have been "only" a few thousand distinct individuals, 600 years ago; and probably "only" a million, 2000 years ago. Still, those ancestors were probably scattered all over the world; and each one of the person's genes may have been inherited from any one of those ancestors, almost independently. (If you are French, for example, you may well be a descendant of the king of the Carijó from Southern Brazil, whose son was taken to Normandy in the early 1500s and there died as a respected citizen, with many children and grandchildren. Recently I learned that, according to ancient historians, some of my ancestors may have came from Paflagonia (not Patagonia!), a kingdom on the northern shore of the Black Sea that I had never heard of before. It is told that they left their country to fight in the Trojan War, and could not return home because of a coup d'état, so they wandered around and finally settled in the marshes where Venice is now. Oh, and I bet that I am also a descendant of Caesar and Cleopatra, through their son who lived in Rome before being forgotten by History.)
No human population on Earth has been isolated from the rest of mankind for more than about 50'000 years. One population of Negritos, in a small island of the Andaman Archipelago, may win the title as the most isolated. To this day, they kill anyone who lands on their island, even shipwrecked sailors. They have been there for 60'000 years, perhaps, since the sea level rose and the land bridge to the Andaman was submerged. But no one knows how long they have been applying that highly selective immigration policy. Anyway, 60'000 years may be enough for natural selection to change some vital traits (like resistance to local parasites, tolerance to local diet, and making enough melanin to stand in the tropical sun without your skin immediately divorcing you), but not enough for really fundamental changes.
No culture has been so strict about racial purity that it could prevent "foreign" genes from jumping the fence and climbing through the window. Even the "modern men" of Europe are now known to have interbred with the "primitive" Nanderthals that they replaced some 30'000 years ago. African and Asian individuals have been traveling and settling down in Europe, and vice-versa, since humans developed feet.
Fact is, we are all of the same race -- the Mongrels...