But if enough of us are infected and undergo personality changes, will that also alter our combined personalities or our culture?
Lafferty admits anthropologists are not likely to embrace his theory. A single powerful leader can have a dramatic impact on a culture. We can all think of examples. But can the collective personality have a similar effect?
"Anthropologists are not in agreement that you can drive a culture from the bottom up," Lafferty says.
But he sees that happening throughout the parasitic world, involving many types of animals, so why is it inconceivable that it could also be happening among humans?
It will be a long time before we have the answer to that, if we ever do, but in the meantime here's a bit of good news.
Cat lovers need not get rid of their cats. The chances are not great that a modern cat, kept on a diet of safe cat food and not left to feed off rats, will transmit the parasite to humans. It's possible, but not likely, Lafferty says.
He ought to know. As a kid he had cats, so after he got into this line of research he assumed he had been infected with the parasite.
"So after I submitted the paper I put down my 30 bucks and got a blood test," he says. "It came out negative. I was so surprised."
And that leads him to this final comment:
"This isn't about trying to freak cat owners out," he says. "Simply having a cat as a pet doesn't mean you're going to get infected, for sure."
Of course, maybe some other parasite is making him say that.