I've stumbled upon Diseases and Peculiarities of the Negro Race by the 19th century scientist Cartwright and found this quote very interesting:
They wander about at night, and keep in a half nodding sleep during the day. They slight their work,--cut up corn, cane, cotton or tobacco when hoeing it, as if for pure mischief. They raise disturbances with their overseers and fellow-servants without cause or motive, and seem to be insensible to pain when subjected to punishment. The fact of the existence of such a complaint, making man like an automaton or senseless machine, having the above or similar symptoms, can be clearly established by the most direct and positive testimony.
What I found most interesting:
Cartwright's unwillingness to ascribe motives to the actions of slaves.
His comparison of slaves to machines.
His claim that black slaves don't experience pain like we (the readership) do.
My questions:
How common would you say are opinions like the three above for the era? S.J.Gould thinks Cartwright held a fringe position even in his own era – any thoughts on that?
Do you know more examples of the same or similar points in other sources? Even vague ones (primary literature, authors I could check out, anything really).
Any responses are much appreciated! Thank you.
This work you have found was, as you correctly suspected, part of a larger social phenomenon called scientific racism, which used scientific principles (especially anthropology) to justify the superiority of white people. A popular technique was also comparing the skulls of African people and apes to show how they're similar, proving Africans to be a "lower form of man." I can't recall any other works specifically about slaves off the top of my head, but the general approach Cartwright takes in dehumanizing the slaves and making out their motivations to be instinct or animalistic is very common of this literature. Here's a little quote on penis size and lack of intelligence from 1903. Apparently Christoph Meiners in the second half of the 18th century, so prior to Cartwright, also said that Africans felt less pain than other people, but unfortunately his works are in German so I can't go read them for you. But it sounds like Cartwright wasn't particularly original.
The article on scientific racism is actually one of the finest articles on Wikipedia, in my opinion. It lists many scientific racists you would be able to look into for more examples like the Cartwright one you found.