Sapolsky used that specific language either in his Standford lectures (which are on YouTube) or in his book Behave: The Biology of Humans At Our Best and Worst. I would highly recommend both. Whether he was sighting a study or merely offering a hypothetical that he felt sufficiently confident in, I don't recall, but I trust his expertise and would encourage others to expose themselves to his work to determine their own opinions on the credibility of the viewpoint I've offered.