Are you claiming that before 1859, Europeans and Americans thought that Africans and Asians were as highly developed as Europeans? So was did the South consider iteslf to be enslaving equals before 1859?
Actually, if you go back to earlier periods, such as the time of the Roman empire, Numidians and other Africans were thought of as basically equal. The Romans used Numidian and Gaullic cavalry in similar ways, and showed no signs of thinking that the Gauls were superior to the Numidians.
In earlier times, too, the worst barbarians came from the North--first the Germans who invaded and destroyed the empire, then the Vikings who attacked the coasts of Ireland, England, France, and other civilized countries.
It was a common theory that civilization belonged to the south, and that the further north you got the stupider and more barbaric people were.
Nor did the ancients ever think of the Chinese as a lesser race. It was during the time when Chinese coolies worked on the western railroads that you began to hear that kind of nonsense, about yellow hordes and the like.
Darwin was not singlehandedly responsible for the rise of racism, but Social Darwinism played an important part in it. "Race" was an essentially scientific idea--bogus science from some points of view, although I won't argue that.
The racist version of slavery was likewise a fairly modern invention. In the ancient world, slavery was universal, but they didn't pick on a particular race to enslave. It was just the unlucky losers.
Not in 1859, but 150 years earlier, race and slavery were not tightly linked, and the idea of "equality" in terms of natural rights was in it's infancy. Only when the Enlightenment and the idea of universal human rights caused intractable intellectual conflicts with the economic institution of slavery did it become necessary to construct justifications for slavery based on racial inferiority.
Before that, slavery was pretty much an equal opportunity employer. By 1859, the racial justification for slavery was firmly embedded, based on the bastardization of Biblical sources, not the bastardization of scientific sources.
Don't kid yourself. The Bible and Evolutionary theory have both been abused to justify racial bigotry.