Population geneticists are interested in the criteria for selection because it supposedly identifies the chain that causes the evolutionary process of adaptation but if a culture has a specific number of males and females, eventually all of them mate so all of the selection criteria which occurs in the first couples disappears because they all mate. Those with the preferred criteria, say tall men get selected first but eventually all of the men mate.
The problem for geneticists is the eventual mating of the entire culture. To repeat, everyone reproduces, even the last selected. So there are other factors which affect evolution but geneticists are sort of trying to curate out the later selections.
Quoting from Unz,: “Detection of recent natural selection is a challenging problem in population genetics, as standard methods generally integrate over long timescales. Here we introduce the Singleton Density Score (SDS), a powerful measure to infer very recent changes in allele frequencies from contemporary genome sequences. When applied to data from the UK10K Project, SDS reflects allele frequency changes in the ancestors of modern Britons during the past 2,000 years. We see strong signals of selection at lactase and HLA, and in favor of blond hair and blue eyes. Turning to signals of polygenic adaptation we find, remarkably, that recent selection for increased height has driven allele frequency shifts across most of the genome. Moreover, we report suggestive new evidence for polygenic shifts affecting many other complex traits. Our results suggest that polygenic adaptation has played a pervasive role in shaping genotypic and phenotypic variation in modern humans.
The basic logic is not difficult to grasp. Derived alleles (the novel ones which mutated recently) subject to selection tend to alter their local genomic region in predictable ways. In particular, derived alleles subject to positive selection will exhibit shallower genealogies than ancestral neutral variants. Conventional neutral processes result in the birth of mutations and extinction of ancestral variants at regular intervals as modeled by the coalescent process. Some alleles will increase in frequency rapidly, and some more slowly, but it will be a random affair.”
In practical terms, the great looking people will mate earlier than the rather ordinary people but longer term the best thinkers will get their preferred mates and in the long run everyone mates.
With the expected errors, there are exceptions but exceptions neither prove nor disprove the rule. Over time the better and the worst people integrate into a phenotype and the culture doesn’t get more great people or fewer undesirables.
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