Here’s what Douglass (1818-1895) said in in “The Claims of the Negro Ethnologically Considered,” a commencement address delivered at Western Reserve College on July 12, 1854:
Man is distinguished from all other animals, by the possession of certain definite faculties and powers, as well as by physical organization and proportions. He is the only two-handed animal on the earth — the only one that laughs, and nearly the only one that weeps. Men instinctively distinguish between men and brutes. Common sense itself is scarcely needed to detect the absence of manhood in a monkey, or to recognize its presence in a negro. His speech, his reason, his power to acquire and to retain knowledge, his heaven-erected face, his habitudes, his hopes, his fears, his aspirations, his prophecies, plant between him and the brute creation, a distinction as eternal as it is palpable. Away, therefore, with all the scientific moonshine that would connect men with monkeys; that would have the world believe that humanity, instead of resting on its own characteristic pedestal — gloriously independent — is a sort of sliding scale, making one extreme brother to the ourang-ou-tang, and the other to angels, and all the rest intermediates! [Emphasis added.]
Michael Flannery, “Frederick Douglass, Champion Abolitionist and Former Slave, on Evolutionary Racism” at Evolution News and Science Today:
Science historian Michael Flannery points out that Douglass’s comments preceded Darwin’s On the Origin of Species because the basic idea of the “modified monkey” (Thomas Huxley’s phrase) was in Lamarck (and probably in the air). Douglass didn’t stay in the controversy. As Flannery puts it, “with emancipation barely won in 1865 and the rise of the Jim Crow South and the KKK he had dragons enough to slay.”
But, clear speaker that he was, what he did say was probably enough.
See also: Darwin reader: Darwin’s racism