Intelligence, itself, is NOT a physical attribute and cannot be “bred” or predicted as to where it will show up.
Those whom we call Slavemasters, well, they know that beyond any doubt, despite what you might see them heavily promote to the contrary.
Even Thomas Jefferson knew that was something they – the ruling classes – did not like having to admit more than two hundred years ago, because it would topple them from their undeserved positions of power.
There is a natural aristocracy among men. The grounds of this are virtue and talents.
…There is, also, an artificial aristocracy, founded on wealth and birth, without either virtue or talents: for with these it would belong to the first class. The natural aristocracy I consider as the most precious gift of nature for the instruction, the trusts, and government of society.
…May we not even say, that that form of government is the best, which provides the most effectually for a pure selection of these natural aristoi into the offices of government?
The artificial aristocracy is a mischievous ingredient in government, and provision should be made to prevent its ascendency.
— To John Adams, vi, 223. Ford ed., ix, 425. (M., 1813.), From The Jefferson Cyclopedia – available to view online at the Internet Archive and Hathi Trust.