the historical ignorance is just astounding.

the origin of species was published in 1859, which was a mere two years before the american civil war. the architects of the american system of slavery had no understanding of darwinian theory, for the simple reason that it didn't exist yet. the association is an anachronism, an ignorant one, and one that you generally hear exclusively from religious people that want to whitewash the dominant and decisive role of religion in the history of slavery.

the american slave trade was built on a papal bull. it was neither science nor capitalism that set this off, but christianity. it was back in 1452, the year before constantinople fell to invading turks, that the pope - who was the hegemon over very catholic spain - declared by decree that non-christians (heathens and saracens) may be legally conquered and placed into "perpetual servitude" by christian forces.

and, if you doubt the legal importance of this papal decree, i will present you with the example of ethiopia, which was never colonized because they were found to be christian upon contact.

so, this was the initial justification for slavery - not race, not skin colour and not any feeling of biological superiority at all, but religious exclusionism. strictly legally speaking, africa was not enslaved because it was black, it was enslaved because it was heathen. 

further, the 1452 decree that western slavery descends from has it's origins in earlier decrees by muslim caliphs, who had previously enslaved all non-muslims. so, not only is western slavery fundamentally a christian thing, but the christians were just copying the muslims in their implementation of it. slavery, as we understand it, is completely religious in origin and scope, through and through.

"but the church opposed slavery!".

the reality is that this statement is misleading at best and, if we are to be truly honest, should be labeled flat out wrong. the reason that the abolitionists used conversion as a tactic was to undermine the law in the first place, because they knew that if they christianized the slaves then it would undercut the argument for enslaving them. so, i mean, give the abolitionists credit for using a smart tactic, but don't give the church credit for opposing slavery - that would be a distorted concept of history, at best.

in fact, it was the church that first started to appeal to biology by citing biblical passages about the curse of ham, but this didn't start to happen until after the abolitionists got off the ground. when biology was used as a justification for slavery, it was done so by the church (by citing the bible.), and not via any scientific body. further, the church only started using biology as a justification for slavery after the slaves started converting to christianity, thereby denying them of their initial justification.

and, you can get into the whole catholic v protestant thing regarding this, and the question of what authority the pope had, and why citing the bible would be more convincing than citing a papal bull, if you were a protestant rather than a catholic. but, this is secondary to the basic point, which is that slavery was a religious institution that was upheld by the church using whatever arguments it could come up with. 

after the end of slavery, it is true that religious leaders tried to co-opt science for their own end, but there were never any scientific institutions running these bodies. the history of eugenics in the united states and canada is mostly tied into the history of sectarian infighting, and was pushed almost entirely by religious bodies. remember: hitler was a catholic, not an atheist. we're walking back down this road of conservative propaganda, again....

broadly speaking, the role of eugenics in the united states was to stop catholics and heathens from breeding. if you read their writings, these people make it clear that they're being driven mostly be sectarianism, not race. but, even insofar as they adopted ideas like "racial hygiene", they interpreted them entirely through sectarian filters - the calvinists naturally thought that they were the master race, whereas the baptists thought they were the master race and etc.

the scopes monkey trials were in the 1920s, and i'm just citing that to put the situation in context - from 1865-1930, much of the united states was strictly under religious rule, meaning you had to run virtually everything by the religious authorities, which would interpret it as they saw fit. there was no room for science as an independent political ideology, during this period. so, i can cite specific examples, but it's best to put the era in context - to exist in america at the time meant that you were an extension of the local religion, which was deeply intertwined with the state. there was no independent thought, no movement outside of the church. so, if the government did things like pass sterilization laws, it was done because the religious authorities desired and sanctioned it - not due to some exotic theories being discussed in distant europe.

and, as our understanding of evolution has advanced, we've discarded most of these ideas as unscientific, altogether.

broadly speaking, the era of european and american slavery was from about 1500-1850, which is a period that preceded darwinism. trying to argue that darwinisim was a factor in slavery is consequently anachronistic and disingenuous. however, much of the capitalist theory that social darwinism (a pseudo-science that attempts to speciously apply capitalist economics to darwinian science.) relied on did exist, and was formative on at least the late stages of slavery, when it became more of a business.

the roots of slavery, though, are actually in the crusades, and the struggle between christians and muslims over europe and the middle east, a struggle in which they enslaved each other by mutual decree. africa very much got caught up in the middle of this, as the christians sought ways to bypass the muslims to reach markets in asia.

your blame should be directed at organized religion, and the judaic form of it most particularly, and not at the enlightenment principles of science that helped us work through all of these problems that organized (judaic) religion created.