I'm going to nitpick a couple points here.

"There is considerable psychological variance between dog breeds: in 1982-2006, there were 1,110 dog attacks in the US that were attributable to pit bull terriers, but only one attributable to Border collies"

Though pit bull terriers are indeed much more dangerous than collies, it may not be entirely behavioral genetics. Unlike collies, pits are often trained to be aggressive. Pits are also simply much stronger and more resistant to pain than than collies, so their attacks are more difficult to defend against, and thus more likely to cause injury, and thus more likely to be reported.

"A larger population means there's more genetic variance: mutations that had previously occurred every 10,000 years or so were now showing up every 400 years. "

True, but a larger population also means that "genetic sweeps" would take longer, especially given our relatively long life spans. If agricultural humans evolved more rapidly I'd say it was more likely due to new selection pressures that their hunter-gatherer ancestors didn't have.