He's essentially solving many of his own "mysteries," as he talks. He is oblivious to what he is actually saying.
The invasion of the longheads was neither a myth nor fallacy. It is a fact that became politically unacceptable. The Normans brought most intelligence to the British Isles. Their brains were bigger.
Go here to see his ambiguous drivel about "increased efficiency" shot down. Do these creatures seem more efficient to you? Here? Here? Vegetables. Flat-lined. Comatose. Less than zero. Not really human any more, something less.
If you can't answer this question correctly, just how big is your own brain?