Presumably, before birth control, the upper class had larger numbers of offspring who survived to the age of reproduction than the lower class did, due to having more resources to support children. In order for there to continue to be an upper class, many of those who had upper class parents did not inherit much wealth and thus often became lower class. For example, Tom Abu said:

...Genghis Khan was prolific in his production of children, to the point where perhaps 0.5% of the world's people are descended from him from him, or at least have his DNA. In a world of 7 billion people, that would be 35 million people.

On the other hand, only four descendants through his wife Bortei inherited the Mongolian Empire after he died. (It was split into four pieces.) And those pieces were later (mostly) recaptured by China, Iran, Russia, and Kazakhstan. Unless you were a descendant who "made a deal" with one of those four countries (or Mongolia) to keep an even smaller chunk.

So, some of the offspring of the upper class stayed in the upper class and some went into the lower class, whereas the lower class almost always stayed in the lower class. Did this lead to society becoming more genetically similar to the upper class?

closed as unclear what you're asking by Semaphore, Mark C. Wallace, Bregalad, Jeroen K, Tom Au Sep 24 '15 at 23:34

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    Please research your assumption that the upper and lower calss where genetically dissimilar to begin with. – mart Sep 23 '15 at 5:59
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    There's no dissimilarity to begin with. The "upper class" is not some sort of genetically distinctive subrace of humans. Even if you restrict this to examples of foreign invaders becoming the ruling class, assimilation typically occurs through intermarriage. – Semaphore Sep 23 '15 at 6:25
  • @Semaphore I am not saying that the difference within the classes is larger than the difference between them. I am saying that there are still some genes that are common in the upper class and less common in the lower class. – Kelmikra Sep 23 '15 at 6:55
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    @Kyth'Py1k That's faulty reasoning. That there's a genetic difference between everyone, is no support for your premise that there's a distinct genetic marker for the "upper class" versus the "lower class". – Semaphore Sep 23 '15 at 7:42
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    I'll downvote any question that begins with an undocumented assertion "presumably ....". I'll downvote almost any question that links history to racism/genetics. I'll downvote this question for presenting a source that doesn't mention class and then making unsupportable conclusions about class. Class and genetics are not simple terms; if they're used without proper care, they tend to be toxic. – Mark C. Wallace Sep 23 '15 at 8:45

It looks like the answer is yes: the lower class did tend to become more genetically similar to the upper class. Azar Gat in "So Why Do People Fight? Evolutionary Theory and the Causes of War" explains:

Some light is shed on the question by a remarkable study recently conducted on the Y (male) chromosome in Central and Eastern Asia, which demonstrates how great rulers’ reproductive advantage could be (Zerjal et al., 2003). It reveals that some 8% of the population in the region (0.5% of the world’s population) carry the same Y chromosome, which can only mean that they are the descendants of a single man. Furthermore, the biochemical patterns indicate that this man lived in Mongolia about a thousand years ago. It was not difficult to identify the only likely candidate, Chinggis Khan, an identification confirmed by an examination of the Y gene of his known surviving descendants. This, of course, does not mean that Chinggis Khan alone sired so many children from a huge number of women, an obvious impossibility even if he had ceased his military conquests altogether. The tremendous spread of his Y chromosome is due to the fact that his sons succeeded him at the head of ruling houses throughout Central and East Asia for centuries, all enjoying staggering sexual opportunities. To be sure, Chinggis Khan was among the greatest warlords ever, and his dynasty probably the most successful. Countless unsuccessful bidders for power, whose lines ceased because of their failures, have to be figured into the other side of the equation. All the same, the apex of the social pyramid held such a powerful attraction for people because it was there that evolution-shaped human desires could be set loose and indulged on a gigantic scale. On a more modest scale, the same considerations held true farther down the social hierarchy.

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    If two classes start to share genetics, they become similar in general. Upper and lower class does not exist genetically. In this case, a lot of people became more similar to C. Khan. But it is very important to understand that there is no upper class gene! – swr Sep 23 '15 at 16:33
  • @swr I know. What made you think I thought there was a single gene that differentiated the upper and lower classes? – Kelmikra Sep 23 '15 at 21:14
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    Because you wrote that the upper class "went into the lower class" and even without being freudian that sounds like the upper class have some kind of upper hand. Genetically speaking. – swr Sep 24 '15 at 7:04
  • @swr Oh, sorry for the misunderstanding. In a sense, the upper class had an upper hand, but it could have been entirely non-genetic. They could have simply by luck found themselves born into the upper class or in some situation in which they are able to exploit others to get into it. – Kelmikra Sep 24 '15 at 22:08

Upper classes normally have fewer offspring than lower classes. In general, a couple will have as many children as they believe they can support in a lifestyle similar to their own.

"Parents sat down and consciously tried to decide, 'How many children can we afford to put through middle school,'" Low told LiveScience. livescience

Note that this citation assumes that children are planned; this is probably not the case in Ghengis Khan's myriad children, most of whom I believe did not arise from couples planning their mating and child rearing, but rather from rape.

Upper classes also normally limit their mating selection in order to preserve class structure; sex outside of class structure may occur, but the children are not recognized; it is impossible to predict the impact of illegitimate children on your hypothesis. Class selection of partners not infrequently leads to inbreeding and reduced fertility (e.g. Romanovs).

Ghengis Khan did not, so far I know limit his mating selection to an upper class individuals; his mating strategy was. (AFAIK) based on rape. It is difficult to discuss class structures when the ruler explicitly excludes the vanquished from any class structure at all. I suspect that the great Khan offered more respect to his horses than to the mothers of his children, or to the children. They were not Mongols, so they could not even be lower class. I don't think we have enough evidence to determine if he believed them to be human.

As I said above, I don't think there is enough formality in your analysis of genetics to measure similarity or dissimilarity. If we generate two sets of random numbers, there is no intrinsic way to compare them. 7 > 5 because we have a number line. Is (3,7,12) more or less similar to (29,128,7) than (7, 223,31)? It is impossible to observe "class" in genetic data.

And it would be an error to formulate any theory based on a dataset which is by definition an outlier. The Khan conquered the world. He is unique. At the moment I am sitting on a slowly moving train. Based on that dataset, I conclude that the entire universe is filled with a pervasive hum and vibration, that my location is effectively random, and that the universe is governed by conductors. Invalid conclusions, but if I trust an aberrant data set I cannot disprove them.

Last night my professional historian girlfriend pointed out that "class" is defined differently in different societies. In the USA class is strongly correlated with wealth, where as in the UK, there is no correlation (to the point that "impoverished nobility" is a trope.) Semaphore points out in this answer that status/class in Mongol society derives from the status of the mother. (and if I am correct, that most of Ghengis' children were born of women with lower status than his horses, that has significant implications on your thesis).

So in summary:

  • Class is an imprecise term that your hypothesis does not define; at a minimum, if your hypothesis is to be tested there needs to be a way to reliably and transparently classify an individual as upper or lower class.Aside(Enter curmudgeon mode) The longer I think about this, the more convinced I am that "class" intrinsically conceals imprecision. I suspect that the meaning of the term shifts depending on the context, the speaker and the time period. Any argument built on these terms is flawed and needs exacting scrutiny.(End curmudgeon mode)
  • The data set you are using to support your thesis is known to be non-representative; conclusions drawn from an outlier data set are suspect. If your hypothesis is to be taken seriously it needs to be tested against multiple other data sets.
  • You haven't defined a methodology to compare sets of genetic data.
  • You haven't supplied a genetic marker for "class" however that is defined.
  • Your hypothesis relies on an assumption (Higher classes have higher reproductive rates) that is suspect (although I need to provide evidence to support my challenge).
  • "Upper classes normally have fewer offspring than lower classes. In general, a couple will have as many children as they believe they can support in a lifestyle similar to their own." This sounds intriguing, but also somewhat hard to believe, as I don't see how people could have evolved to be like this. What are your sources? Also, I agree that using a single exceptional example is weak evidence, so further research would help. I am not entire sure of how to formally measure similarity and dissimilarity in genetics, but measuring the degree of overlap of proteins created seems sufficient. – Kelmikra Sep 25 '15 at 3:58
  • That's basic high school anthropology; I'm having trouble finding a source for something I learned half a century ago, and that is my fault and weakens my answer. – Mark C. Wallace Sep 25 '15 at 11:19
  • Interesting. Do you think it would be appropriate to ask about the causes of this on SE? – Kelmikra Sep 25 '15 at 21:52

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