Humans are fundamentally social animals. Our social nature means that we interact with each other in positive, friendly ways, and it also means we know how to manipulate others in a very negative way.

Neurophysiologist Katherine Rankin at the University of California, San Francisco, has also recently discovered that sarcasm, which is both positively funny and negatively nasty, plays an important part in human social interaction.

So what?

I mean really, who cares? Oh for God's sake. Don’t you have anything better to do that read this column?

According to Dr. Rankin, if you didn’t get the sarcastic tone of the previous sentences you must have some damage to your parahippocampal gyrus which is located in the right brain. People with dementia, or head injuries in that area, often lose the ability to pick up on sarcasm, and so they don’t respond in a socially appropriate ways.

Presumably, this is a pathology, which in turn suggests that sarcasm is part of human nature and probably an evolutionarily good thing.

How might something so, well, sarcastic as sarcasm, be part of the human social toolbox?

Evolutionary biologists claim that sociality is what has made humans such a successful species. We are masters at what anthropologists and others call "social intelligence." We recognize and keep track of hundreds of relationships, and we easily distinguish between enemies and friends.

More important, we run our lives by social calculation. A favor is mentally recorded and paid back, sometimes many years later. Likewise, insults are marked down on the mental score card in indelible ink. And we are constantly bickering and making up, even with people we love.

Sarcasm, then, is a verbal hammer that connects people in both a negative and positive way. We know that sense of humor is important to relationships; if someone doesn't get your jokes, they aren't likely to be your friend (or at least that's my bottom line about friendship). Sarcasm is simply humor's dark side, and it would be just as disconcerting if a friend didn’t get your snide remarks.

It's also easy to imagine how sarcasm might be selected over time as evolutionarily crucial. Imagine two ancient humans running across the savannah with a hungry lion in pursuit. One guy says to the other, "Are we having fun yet?" and the other just looks blank and stops to figure out what in the world his pal meant by that remark. End of friendship, end of one guy's contribution to the future of the human gene pool.

Fast forward a few million years and the network of human relationships is wider and more complex, and just as important to survival. The corporate chairman throws out a sarcastic remark and those who "get" it laugh, smile, and gain favor. In the same way, if the chair never makes a remark, sarcastic people are making them behind his or her back, forming a clique by their mutually negative, but funny, comments. Either way, sarcasm plays a role in making and breaking alliances and friendship.

Thanks goodness, because life without out sarcasm would be a dull and way too nice place to be, if you ask me.

Meredith F. Small is an anthropologist at Cornell University. She is also the author of "Our Babies, Ourselves; How Biology and Culture Shape the Way We Parent" (link) and "The Culture of Our Discontent; Beyond the Medical Model of Mental Illness" (link).