This is true --- if normal means typical: "Normally, men in the educated professions wear white powdered wigs" -- true for 1750, because typical for 1760.
But it is not true if normal means full-functioning according to its nature. With this meaning, for example, deafness isn't normal, even if you're at Gallaudet.
A white boy dating a black girl might not be normal (typical) for 1750, 1850, or maybe even 1950, but it would still be normal (well-functioning) if we assume that dating is motivated by sexual attraction. It is normal for a male to be attracted by a female, because sexuality is full-functioning only in relation to sexual union ("the union of the sexes" -- this required two sexes) and procreative potential.
Sounds like it depends a lot on one’s definition...sort of relative