In the American genus cebus, the various forms are ranked by some naturalists as species, by others as mere geographical races.
"The Descent of Man and Selection in Relation to Sex, Vol. I (1st edition)"
Charles Darwin
Now if numerous specimens of cebus were collected from all parts of South America, and those forms which at present appear to be specifically distinct, were found to graduate into each other by close steps, they would be ranked by most naturalists as mere varieties or races; and thus the greater number of naturalists have acted with respect to the races of man.
"The Descent of Man and Selection in Relation to Sex, Vol. I (1st edition)"
Charles Darwin
14, 20. On cebus, Brehm, ibid.
"The Descent of Man and Selection in Relation to Sex, Vol. I (1st edition)"
Charles Darwin