If you want uniformity in your breed there is only one way to achieve it: through inbreeding. If you want diversity, there is only one way to achieve it: let these breeds to mix. You cannot have it both ways. There is hardly any equality between the Great Dane and chiwawa: the continuum of variation in dogs is much broader than it is in humans. Our genetic endowment is simply too restrictive to produce very wide variation. We may have exceptional individuals, but they are exceptionally rare: most abilities are distributed around the middle with a very small number of outliers. It is this property of traits variation that makes us equal (Hobbes' argument). The question is what makes us different from dogs, and the suggested answer is that it is culture. Culture divides us in so many kennels where we inbreed and makes breeding between kennels infrequent. It is this mechanism that sustains low genetic diversity, which is the basis of equality. If you remove such barries, there will be cross mating and diversity will explode. We know how to live in the world where there is 0.1% Einsteins and 90% can understand that 2x2=4. You will get the world where there will be 10% Einsteins but only 30% can understand that 2x2=4. The spectrum of ability will dramatically expand, just like it does in animals that have geographical barriers, but no cultural ones. With such a broad spectrum of ability, achieving equality becomes a harder task. You cannot have it both ways.
Now, about the dangers of inbreeding. We are talking here about pools of 10,000-100,000 individuals - this is not a small number of people, it is a town. But even if it is much smaller, inbreeding is not "bad" per se, as you probably know. Once the bad genes are gone through attrition, if the group remains reproductively isolated, nothing happens. It may have relatively low fitness and it will be unstable to introduction of outside genes (that will reintroduce "bad" genes) but if it manages to remain isolated, it will survive. There were massive experiments in human inbreeding (e.g., among Roman Egyptians) that lasted for centuries. They did not survive to our days, but so did the Romans.
I understand how inbreeding keeps genetic variety low within human kennels, but what I fail to understand is how it works out to keep the diversity low throughout the humanity - wouldn't different kennels start drifting away from each other creating different human breeds similar to dog breeds? Low variety among a given kennel, but not BETWEEN different kennels..
There are much fewer kennels than dogs. Because each kennel is inbred (very low variation) you can think of it as an individual; there are only so many representative "individuals" mating in the general population, so the effective population size becomes low eventhoug the total population is large. So not only genetic diversity inside the kennel is low, it becomes low in general. Perhaps an analogy with ants would be more apt than the analogy with dogs. There are trillions of individual ants, but because mating groups within each ant hill are small, their genetc diversity does not scale with their total size.
There is another possibility: "cultural hitchhiking." Eg, the inventors of agriculture had a huge edge over the others and one can observe the concentric circles of replacement and variation gradients around the first centers of agriculture. People with some important cultural innovation can physically replace or outbreed the others, if cultural diffusion is slower than genetic one. In this case you will have inbreeding and low diversity, eg http://www.des.ucdavis.edu/faculty/richerson/Whitehead%20for%20Selection%2006%2002.prn.pdf So the idea is cultural group selection replacing the reliance on genetic variation.
In fact, such explanations are almost certainly correct. Since a bottleneck requires convergence of different patterns in time, it would be easy to spot, but after two decades no such convergence was observed for different loci, so this kind of rationale does not work. Geogrpahical patterns certainly hold, but they too cannot explain the observed degree of genetic similarity. By exclusion it leaves cultural effects. he substructuring should be cultural, but the precise mechanism is elusive (there is more than one way in which culture can promote genetic uniformity). The important point is that any promotion of cultural diffusion and lowering of cultural barriers inevitably leads to increased genetic diversity, as this low diversity is wholly artificial. But that kills the main physical premise of human equality, see Ch XIII of Leviathan, http://shkrobius.livejournal.com/149462.html
Now, about the dangers of inbreeding. We are talking here about pools of 10,000-100,000 individuals - this is not a small number of people, it is a town. But even if it is much smaller, inbreeding is not "bad" per se, as you probably know. Once the bad genes are gone through attrition, if the group remains reproductively isolated, nothing happens. It may have relatively low fitness and it will be unstable to introduction of outside genes (that will reintroduce "bad" genes) but if it manages to remain isolated, it will survive. There were massive experiments in human inbreeding (e.g., among Roman Egyptians) that lasted for centuries. They did not survive to our days, but so did the Romans.
In fact, we are all children of incest. Humans have a different number of chromosomes from apes ; the only plausible scenario of losing two of them is through a bottleneck and inbreeding; this happened 2 Mya, e.g. (small words only!)
http://www.slate.com/articles/health_and_science/chromosomes/features/2012/blogging_the_human_genome_/blogging_the_human_genome_why_do_we_have_two_fewer_chromosomes_than_our_closest_primate_relatives_.html
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There is another possibility: "cultural hitchhiking." Eg, the inventors of agriculture had a huge edge over the others and one can observe the concentric circles of replacement and variation gradients around the first centers of agriculture. People with some important cultural innovation can physically replace or outbreed the others, if cultural diffusion is slower than genetic one. In this case you will have inbreeding and low diversity, eg
http://www.des.ucdavis.edu/faculty/richerson/Whitehead%20for%20Selection%2006%2002.prn.pdf
So the idea is cultural group selection replacing the reliance on genetic variation.
In fact, such explanations are almost certainly correct. Since a bottleneck requires convergence of different patterns in time, it would be easy to spot, but after two decades no such convergence was observed for different loci, so this kind of rationale does not work. Geogrpahical patterns certainly hold, but they too cannot explain the observed degree of genetic similarity. By exclusion it leaves cultural effects. he substructuring should be cultural, but the precise mechanism is elusive (there is more than one way in which culture can promote genetic uniformity). The important point is that any promotion of cultural diffusion and lowering of cultural barriers inevitably leads to increased genetic diversity, as this low diversity is wholly artificial. But that kills the main physical premise of human equality, see Ch XIII of Leviathan,
http://shkrobius.livejournal.com/149462.html
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