There’s a whole chapter in superintelligence on human intelligence enhancement via selective breeding
This is false and should be corrected. There is a section (not a whole chapter) on biological enhancement, within which there is a single paragraph on selective breeding:
A third path to greater-than-current-human intelligence is to enhance the functioning of biological brains. In principle, this could be achieved without technology, through selective breeding. Any attempt to initiate a classical large-scale eugenics program, however, would confront major political and moral hurdles. Moreover, unless the selection were extremely strong, many generations would be required to produce substantial results. Long before such an initiative would bear fruit, advances in biotechnology will allow much more direct control of human genetics and neurobiology, rendering otiose any human breeding program. We will therefore focus on methods that hold the potential to deliver results faster, on the timescale of a few generations or less.
Kudos! I see the blog is still hosted at ineffectivealtruismblog.com, though. Fortunately both reflectivealtruism.com and reflectivealtruismblog.com are currently available.