They're jerks, according to this study. It makes sense; if you reward people for focusing on their financial welfare at the expense of all other considerations, then that behavior is going to leak over into other areas.
This is why we don't torture animals; because doing so degrades our instincts and makes us more likely to torture people (the FBI first noticed this while tracking serial killers). Human beings are machines, and like any complex, poorly-designed machine, they have tolerances. Operate them outside of those tolerances for long, and they start to fail.
If anyone ever asks, "How has the theory of evolution affected you?" the answer is right here, in this view of humans as machines, and in this understanding of why we have to have broad moral principles, of why we have to err on the side of caution, of why everything your mother said about jumping off a cliff just because everyone else was doing it makes sense.