 0.3. How can a nook be descended from Confucius? First, I hope I've established for you that everyone in Asia is directly descended from Confucius. Because the populations of Asia, Europe, and Africa have seen a lot of trade and intermarriage, that necessarily means that the MRCA of everyone on that supercontinent is quite recent. What mechanism allows for the genetic mixing to more distant regions? I call it the bucket chain of ancestry because it operates on a similar principle to people passing a bucket of water only a short distance, and yet their actions collectively move water great distances with little effort. A young man from village A marries a young lady from village B, and they set up a family in B. But one of their daughters marries a man from C, and they raise their kids who go on to D and E. The only boundaries are large geographical ones and the smaller cultural ones. We do see intermarriage between cultures, say Jewish and Muslim, or Norman and Saxon, and not all babies are the result of a lasting love between two people. Rape, sex trades, and prostitution, especially in port towns, provide a way for the bucket chain to break through these culturally enforced barriers. What about geographical barriers? This is considerably more challenging. Consider Australia though. Centuries prior to European colonization, the Australian Aborigines certainly had contact with what is now Papua New Guinea, and they in turn had contact with the Asian mainland. I think where many people fail is to imagine a single adventurous soul walking and boating from Siberia to Canberra, when instead we are talking about a multi-generational bucket chain that involves a web of thousands of individuals, each establishing a new air no more than a few dozen or so miles from where they themselves were born. What about the great leap between old and new world continents? That is a bit of a challenge, but we can meet it in at least two ways. One, we can speculate a little bit on the ancient bucket chain across the most narrow points. For example, there are Eskimo tribes belonging to a group called the Yupik on both the Alaska and Siberia sides of the Pacific divide. They speak a common and very distinctive language, but they are known to have traded and possibly intermarried in Asia and North America for centuries. Eskimos were also found in Greenland, and this may have been one of the first encounters of the Europeans, in this case probably Viking explorers with North Americans. The Vikings as you may know had established colonies in modern day Canada, as far back as 1000 AD. Now, were any blue-eyed babies born in native villages around Vinland? It seems likely, but it's not required for our model. The second way to satisfy our model is with recent colonization. Columbus marked the beginning of the boom of European colonization in the Americas, so we can assume about 1500 as the point where a restored gene flow can be really documented. That gives us about 500 years or 25 generations, more than enough American-born Europeans to be the ancestors of every living person with Native American ancestry. South America in particular shows the sign of being a mixing bowl of European and Native American ancestries. So regardless of whether the bucket chain model of ancestry is valid or not, whether or not the Eskimos acted as a genetic bridge across the Pacific or the Atlantic to make an mictic populations of Eurasia, we still have enough time and ancestors to make Confucius or any other figure of about the same time period be the direct ancestor of all living people. Now perhaps the Sentinelese or some other island-bound population isolated deep in the middle of the Pacific contain on their shores a few individuals who cannot count Confucius among their distinguished line. But for the majority of the world's population, I feel pretty safe in saying that we all share that distinguished figure in our direct line. Point four, how does this relate to the biological significance of race? To some extent not very much. I want to make sure I'm clear that just because we share a common ancestor in very recent history doesn't mean that we are genetically homogenous. Someone born in Beijing is going to look Chinese because most of their ancestors were of a Chinese population, most likely the Han. They have Australian ancestors as well, but the fact that each generation can only pass on half their genes means that any single ancestor's contribution rapidly gets diluted out to practically nothing. This is not a genetic bucket chain, it's a chain of ancestry only. However, I think this is significant. We all have a vested stake in the history of all peoples. I want to reintroduce the ancestry pyramid and we'll look at your ancestors only a few dozen generations ago. There were millions of them and they came from many places on earth. That mixing of lines to me destroys the idea of essentialism that pervades racist or racialist ideas. There are no Nordic people without an African ancestor in the very recent past. There are no pure peoples anywhere so far as we know. The consequence of the models that have been constructed is that no two people on earth are more than about 40th cousins. Our ancestors in the Bronze Age are the same for everyone alive, which is really pretty profound. The raced realists have one thing nearly right. The differences that everyone focuses on are real. Africans really do have dark skin and a certain type of hair, except when they don't. East Asians really do have epicampal folds, except when they don't. What most people think of as scientific evidence of race is actually only evidence of a common ancestry link in a large group of people. If your great whatever grandfather had a genotype for a certain type of nose for example and you also have it, then you can be put into a bin of people who have a certain type of nose through common ancestry with your great whatever grandfather. However, what you share in common with those other people is not very significant beyond a shared great whatever grandfather. When I say that race is a social construct, I'm referring to the fact that while ancestral lines exist and they may be marked by visible phenotypes like your great whatever's nose, they don't constitute a biologically significant group. This kind of thinking ignores the realities of the genetics. Many people in comments have used the dog analogy, which is a real mistake for them. Dog breeds are real, but they're the result of AKC standards, a type of societal construct, of hundreds of generations of selective inbreeding, and even then there is no lasting identity to a dog breed. Inner breed chihuahuas and labradors for a few generations, and they won't look like either breed. These are not fixed values. Race is not written in your DNA. Am I some politically correct, liberal, pot-smoking hippie, or do I represent the mainstream of science? I want to read a short section to you from the American Anthropological Association's statement on race. Because physical traits are inherited independently of one another, knowing the range of one trait does not predict the presence of others. For example, skin color varies largely from light in the temperate areas in the north to dark in the tropical areas in the south. Its intensity is not related to nose shape or hair texture. Dark skin may be associated with frizzy or kinky hair or curly or wavy or straight hair, all of which are found among different indigenous peoples in tropical regions. These facts render any attempt to establish lines of division among biological populations, both arbitrary and subjective. Historical research has shown that the idea of race has always carried more meanings than mere physical differences. Indeed, physical variations in the human species have no meaning except the social ones that humans put on them. Racial beliefs constitute myths about the diversity in the human species and about the abilities and behavior of people homogenized into racial categories. The myths fused behavior and physical features together in the public mind, impeding our comprehension of both biological variations and cultural behavior, implying that both are genetically determined. Racial myths bear no relationship to the reality of human capabilities or behavior. Scientists today find that reliance on such folk beliefs about human differences in research has led to countless errors. If you want to look for justification for your particular brand of bigotry, I'm afraid you'll have to look elsewhere. Science where it concedes that diversity exists both within and between groups doesn't subscribe to your dogma. Thanks for watching.