The blank slate theory has been thoroughly debunked by a number of researchers as was the equally loony theory that all the people of the world have the same physical properties. In short, they were trying to claim that while every other living species on earth evolved into different forms, man was an exception.
Except the truth is man was not an exception. There are differences other than skin color between the peoples of the world. Bad news for liberals and leftists (people like Jared Diamond and Steven Jay Gould) who wanted to blame luck and circumstance for the differences in quality of life for the world's denizens.
It's true that luck and circumstance are at work - via the genes any given creature (human or otherwise) inherits. The problem with the whole topic, however, is that - at present - it’s a true dismal science (unlike economics, which is neither truly dismal nor a science). There’s not much that can be done about a person’s essential characteristics once he’s born. Calvin was right, but with genes being the mechanism of divinely-ordained determinism.