It's simple to say "let's have a fatter cow". It is not simple to say "let's have a more intelligent human" because "intelligent" is not a fixed or agreed term.

100 years ago people would have thought mental arithmetic, memorization and rhetorical speech were core parts or indicators of intelligence. I think that most people today would see creative problem solving, social empathy and long term planning as more indicative. In fact the 19th century indicators are now seen (in popular culture) as part of a disorder (autistic spectrum) that is often used to explain the behaviour of otherwise incapable people.

Our culture, communities and technology define our humanity, creating a greater humanity through breeding misses the point somewhat.

Or rather, Pokemon breeding has slowed its roll at zoological notes (rather than incubation for reproductive adjuncts and agonists,) ashram automation hasn't encapsulated all that much microbiology and safety vetting at once, motivators for diversity are copacetic, emphasis on surviving (humanity) long enough to learn and use something is well-vetted, not everyone has replaced themselves with a short dna/rna script, and that the script for talking with your S.O.'s parents just doesn't always veer toward on-point superinfection and reproductive health in the window allotted.

A baby monitor with progress notes on various pivot options sounds great. (Revolutionary Girl Utena model Serta...) It beeps if all the child's career options are deprecated by the next 15 years, and points to an appropriate hill near which those careers fester; or if their social health role is to force vulnerable mutations in (otherwise) epidemic disease (I'm only a Doctor ironically, etc.)

Intelligence might not be a fixed or agreed term, but GCA is fixed and agreed. If you can measure a genetic trait, and the trait varies in the population, then you can bring about population level changes in this trait via selective breeding.

Of course this does not mean eugenics is a desirable activity that we should be engaged in, but I have not seen any rational argument that it has been “proved" to be impossible.

I think GCA originated in 1954; I don't know how many generations of people breeding it would take to get a selected trait - humans are genetically very similar compared to other species; there is not much variation... so I don't have any idea of what the breeding program length would be, but I assume that it would be several generations... so I don't think that an idea that has been around for 60 years would really qualify as fixed and agreed in that time scale.

Also I don't think it's agreed.

Also it's not clear that your statement that population level changes can be created by selective breeding is true - if a characteristic is dictated by alleles that damage fertility or other fitness indicators then it may well not be continuous. In the case of human intelligence the increased child birth mortality associated with large heads and the increase dependence of infants on parents are examples. There may be others which are more relevant to modern life, like propensity to depression, disinterest in sex etc (note : I am using these as examples, not saying that this is so).

If there are some individual in the population with the particular phenotype you are selecting who are not infertile then selective breeding can increase the frequency of that phenotype in the population. In the case of GCA we know that there are fertile individuals with very high GCA so we know it is possible to selectively breed for high GCA.

Of course selecting only for GCA may well increase the frequency of other phenotypes, but unless GCA is directly linked to that phenotype then there is no reason you can’t select against any undesired phenotype at the same time. This is done all the time with the selective breeding of animals and plants. I know of no phenotype shared by all individuals with a high GCA so there should be no phenotype that would inherently be a consequence of selecting for high GCA, certainly not infertility.

> I don't know how many generations of people breeding it would take to get a selected trait - humans are genetically very similar compared to other species; there is not much variation... so I don't have any idea of what the breeding program length would be, but I assume that it would be several generations

Use whole-genome mutagenesis and increase the size of your population. This will reduce the total number of generations that you require to find the novel mutations that you seek.