Assortative mating is a nonrandom mating pattern in which individuals with similar genotypes and/or phenotypes mate with one another more frequently than would be expected under a random mating pattern.Assortative mating almost certainly happens:
The old saw notwithstanding, opposites do not really attract when it comes to love and marriage. Likes attract. In one of the classic papers, originally published in 1943, two sociologists studied 1,000 engaged couples in Chicago, expecting to find at least some traits in which opposites did indeed attract. But out of fifty-one social characteristics studied, the sign of the correlation was positive for every single one. For all but six of the fifty-one traits, the correlations were statistically significant. [...]
Of the many correlations involving husbands and wives, one of the highest is for IQ. [...]
Christine Schwartz and Robert Mare examined trends in "assortative marriage," ... from 1940 to 2003. They found that homogamy has increased at both ends of the educational scale -- college graduates grew more likely to marry college graduates and high school dropouts grew more likely to marry other high school dropouts. [...]
In 1960, just 3 percent of American couples both had a college degree. By 2010, that proportion stood at 25 percent. The change was so large that it was a major contributor to the creation of a new class all by itself. [...]
Bit increased educational homogamy ... inevitably means increased cognitive homogamy.I'd like to go beyond just considering cognition though. Imagine all successful people across all human endeavors. Leave out those that are successful overwhelmingly due to luck. Consider all positive traits that are more common among those successful people than the general population. Those traits no doubt have at least some intersection with cognition and the "fifty-one social characteristics" above and might include things like perseverance, impulse control, drive, learning ability, creativity, curiosity, ability to work in teams, leadership, followership, etc.
Let's call that suffectiveness. Suffectiveness is a combination of "success" and "effectiveness" or those human traits that are generally effective towards achieving success given the current state of civilization. It ignores specific characteristics that are useful in specialized endeavors. Ability to play brass instruments would be an example of a characteristic which is good but not part of suffectiveness.
If mating were completely random, the distribution of suffectiveness would likely resemble a bell curve. If suffectiveness is at least partly heritable and if assortative mating occurs to some extent (which it does), the distribution of suffectiveness would change.
Is suffectiveness heritable? To some extent, very likely. For example, IQ is likely at least partly related to one of the sub-traits of suffectiveness and IQ is very likely at least partly heritable:
The general figure for heritability of IQ is about 0.5 across multiple studies in varying populations.I decided to do some modeling. There's no way to completely accurately model the suffectiveness of a human population, so I made some simplifying and extreme assumptions. The model population is 100,000 for each generation, with each female having exactly two children. Each individual has 23 pairs of chromosomes, coincidentally the same number of chromosomes that humans have. On each chromosome, there are arbitrarily 12 gene complexes that add to the suffectiveness of the individual if present. The total suffectiveness of the individual's genotype is the sum of all present suffective gene complexes across all of the chromosomes. I'm not considering dominant and recessive genes for this model. Since there are 46 chromosomes (23 pairs), and 12 gene complexes per chromosome, there can be a maximum of 552 suffective gene complexes present.
Each individual is able to exactly tell the suffectiveness of another individual just by observation, except that a small random amount of suffectiveness is added to the sum of the suffective gene complexes. The small random amount for these trials had a mean of zero and a variance of 2.76 gene complexes. This was added mostly to keep the curves smooth but the original reason was to keep the sorting from be too rigid and to provide a distinction between genotype and phenotype. I call the total suffectiveness including the random addition the phenotype suffectiveness.
The first model is an assortative monogamous mating model. Each generation is sorted by phenotype suffectivness. One of each of the 23 alleles is taken whole (no chromosomal crossover) from each paired male and female when generating the chromosomes for the offspring. The following graphs show the phenotype suffectiveness for generations 1 (the original), 2, 3, 9, 33, 129, and 257.
|Assortative Mating - Original Distribution|
|Assortative Mating - Generation 2 Distribution|
|Assortative Mating - Generation 3 Distribution|
|Assortative Mating - Generation 9 Distribution|
|Assortative Mating - Generation 33 Distribution|
|Assortative Mating - Generation 129 Distribution|
|Assortative Mating - Generation 259 Distribution|
In the model above, no chromosomal crossover was allowed. In other words, alleles were never allowed to be formed by mixing any of the gene complexes. In real life, some crossover does take place. In the second model, I allowed an extreme version of chromosomal crossover, where any of the suffective gene complexes were randomly allowed to crossover intact.
The results did not differ noticeably for about 30 generations, where the changes in distribution from selection of entire chromosomes was such a large factor that crossover had relatively little effect. After the 30th generation or so, the differences relative to the first model became more apparent. The following graphs show the suffectiveness for generations 33, 129, and 257, 513, and 1025.
|Assortative Mating with Crossover - Generation 33 Distribution|
|Assortative Mating with Crossover - Generation 129 Distribution|
|Assortative Mating with Crossover - Generation 257 Distribution|
|Assortative Mating with Crossover - Generation 513 Distribution|
|Assortative Mating with Crossover - Generation 1025 Distribution|
Chromosomal crossover enables further concentration of the suffective gene complexes (and lack thereof) leading to an even wider variance and more extreme distribution of suffectiveness. Perhaps in enough generations, these two extremes will resemble H.G. Wells' Morlocks and Eloi?
The two models above were monogamous mating models. Even without the genetic drift shown by the models, assortative monogamy still leads to inequality. Even with wealth redistribution, there will still be a radical inequality of suffectiveness per household. At one end, Ph.D.'s marry Ph.D.'s, at the other end, unemployed sewer workers marry part-time barmaids. Not that there's anything wrong with sewer workers and barmaids, but the point is that the two households will have nothing in common and will hardly even be able to talk to each other. It will likely only get worse over time even with no genetic component. I believe that this sort of inequality will be both an inherent feature of monogamy going forward and that this inequality is far more destabilizing than mere wealth inequality.
Many societies in the past and present are not monogamous and as I've pointed out in other posts, monogamy is becoming less popular now in the United States (and the rest of the world) as well. Monogamy has many good points and was, in my opinion, very likely necessary for civilization to have made it this far. But here we are, and it's not clear to me that it makes sense going forward because it will inherently lead to a particularly destabilizing sort of inequality.
Lets' go back to models. This next model models female hypergamy, which, for the purposes of this post is defined as the natural desire for females to mate with someone of higher status, perhaps or hopefully much higher status. It's debatable to what extent that desire is present in human females, but that's the assumption for the next model.
This model is just like the first model except that only the top fifth of suffective males are used to generate the next generation of offspring. In the first model, each male and female had two children. In this model, each female still has two children. However, each of the top 20% most suffective males has ten children, two with each of five females.
In the graphs from the previous two models, the axes were identical. For this model, the Y-axis expands as the distribution narrows. The following graphs show the suffectiveness for generations 1, 2, 3, 9, 33, and 129 from the female hypergamy model.
|Hypergamy - Generation 1 (Original) Distribution|
|Hypergamy - Generation 2 Distribution|
|Hypergamy - Generation 3 Distribution|
|Hypergamy - Generation 9 Distribution|
|Hypergamy - Generation 33 Distribution|
|Hypergamy - Generation 129 Distribution|
As I mentioned before presenting these models, there are many simplifying and extreme assumptions incorporated into the models. The point is not that the above is a reflection of reality, or to the extent it is a reflection, it's a very, very distorted one. The point of modeling is to get an idea of how potential factors might affect the trajectory of society.
Each person interprets the ideas and information available differently. My interpretation is that monogamy will probably lead to a more unequal society over time and that the particular type of inequality (inequality of suffectiveness and status) will be destabilizing and may more than cancel out the advantages of monogamy, and that women seeking out much higher status males to get them pregnant may not be such a bad thing if we can survive a few generations of that, especially if the other 80% of men are happy to go their own way each generation and play video games and watch porn.