Neoreactionary Society and Dysgenics

On the one hand, neoreactionaries believe in reviving the traditional society (with a hereditary aristocracy and the ability to execute heretics) that governed much of the human race for the past ten thousand years. On the other hand, they also believe in eugenics, especially for the purpose of increasing brain power. On the gripping hand, the traditional-society era also saw shrinking brain sizes. For that matter, brain sizes having been coming back up in the less traditional society of the past few centuries. Wait a moment …

I'm not sure why the shrinkage occurred. Is it because the most successful men were Pointy-Haired Bosses of yesteryear? (ObSF: the Sooners in Brightness Reef by David Brin) Is it because the brightest people were burnt at the stake?

If neoreactionaries argue the same way leftists do, they will no doubt claim that traditional society wasn't traditional enough.