Scientists and psychologists have long debated the nature vs. nurture theory. Are we the way we are because of our genes, our IQ, our parents, the toxins in our tap water? Certainly, some diseases like cancer, diabetes, alcoholism, and depression can be passed on genetically, but it's up for grabs how much environment plays into fully developing something that was lurking in one's gene pool.
But really, all that BS doesn't matter in the end when it comes to these families who share an interest in human flesh, chainsaws, torture, rape, and occasionally each other, if you know what I mean. All that matters is getting the hell away from them as fast as you can.
It's really hard to say which of these disgusting groups of related and/or inbred freaks is the worst, so this is in no particular order. Enjoy!