A study earlier this year found that saints and sinners both tend to find a moral balance, the former by breaking rules and the latter by following the rules.

Carry that theme to the extreme, and you might think, at least, that a sociopath and an extreme altruistic do-gooder are opposites personality-wise.

Increasingly, however, research suggests you'd be wrong.

"After all, the chances of a serial killer running into a burning building to save a child are pretty slim, right?" writes Andrea Kuszewski at ScientificBlogging. "And wouldn't a hero-type be one of the last people likely to break rules?"

Not so, according to a new study Kuszewski cites.

"Personality has consistently shown to be extremely heritable," she writes. "However, the same genetic material arranged and weighted in a slightly different way, may at times express as vastly different phenotypes: the 'extremely good' and the 'extremely bad' individual."

In fact, scientists say natural selection leaves us all at least a little bit crazy — a byproduct, perhaps, of our oversized brains. One might wonder to what extent nurturing determines whether a person ends up on this or that side of the line. (New Scientist)