>>11465716I would define eugenics as an intervention (by means other than natural, kin, or sexual selection) with the purpose of binging about a genetic change at the population level such that the prevalence of undesirable traits decreases, or the prevalence of desirable traits increases. Note that ‘undesirable’ and ‘desirable’ are inherently ideologically defined, since we are talking about selection that does not involve typical evolutionary selection mechanisms. An example of this is selective breeding of livestock to increase milk yield.
In humans, as opposed to narrowly circumscribed populations of livestock / pets, this would not practically work for several reasons.
Humans are exposed to very different environments across individuals, so most of trait variation is not due to genetic factors but to differences in environment. One consequence is that it makes it hard to identify subjects who have desirable genetic characteristics, especially when considering polygenic traits that people would tend to think are desirable based on ideological reasons.
It is possible to measure genetic potential directly from genetic markers and what we know from this is that these genetic predictors perform poorly. We can also tell that there are many important, very rare genetic variants relevant for phenotype which we will never be able to identify. We thus have an absolute ceiling on our ability to assess an individual’s genetic fitness from either their current performance or from their genome and we know that the potential ability to do this is extremely low, far too low to be useful for selective breeding.
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