Cartwright insisted that black people form a species apart from white people. That distinction did not, furthermore, end at the color of the skin. Nineteenth century biology, though in its infancy, still had enough sophistication to recognize different color morphs as distinctions within a species. They certainly didn’t succeed every time, but charity requires us to remember that they lacked the tools we take for granted.
So what did Cartwright work from, if not skin color? The next section of his paper makes for rather hard reading, but we can’t understand his position well enough to dispute it unless we learn how he arrived there.
Cartwright writes that a black person’s
bones are whiter and harder than those of the white race, owing to their containing more phosphate of lime and less gelatine.
One wonders what dissections Cartwright performed to make the comparison. In an addendum answering critics, he stated that simple comparative anatomy would resolve the matter but makes no mention of undertaking the experiment himself. Cartwright simply insists “naturalists universally agree,” despite not finding occasion to cite one as he does for his other claims, to naturalists who did not agree. Furthermore
Herodotus mentions the greater hardness of the Ethiopian skulls; proving, in that respect, at least, that the negro is the same now as he was two thousand years ago.
We know almost nothing about Herodotus’s personal life, but to my knowledge he never claimed any particular medical expertise or reported any experiment that he performed on the matter. Even in Antiquity learned men debated how much or little he cared to verify his claims. (Some called him the Father of Lies, not history.) But let’s spot Cartwright the point and say the doctor did the experiments and found that black people had stronger bones than white people, just for the sake of argument.
What black people would Cartwright have on hand to dissect? Almost certainly dead slaves and, assuming he required permission from the owner, or cut up a slave of his own, he probably did not have a prized house slave but rather a field slave who lived a life of back-breaking physical labor. The same would probably hold for preserved specimens at museums. Exercise strengthens bones and muscles, whether undertaken by a black or white person and whether engaged in for self-improvement or compelled by the overseer’s lash.
Cartwright does not limit his description of skeletal peculiarities to the hardness or hue of bones, though. He says of black people
His head is hung on the atlas differently from the white man; the face is thrown more upwards, and the neck is shorter and less oblique; the spine more inwards
In other words, black people hunch down more than white people and thus have to look up more to see forward. This again sounds like the product of backbreaking work such as, for example, harvesting cotton by hand. A lifetime of that, beginning in childhood, would curve anyone’s spine.
Did Cartwright compare the spines and necks of field slaves with the spines and necks of, for example, white small farmers who would undertake much the same labor? He makes no mention of doing so despite frequent references to comparative anatomy.