Editor's Letter: The evolutionary drive of microbes

last updated 8 January 2015

Why do we do the crazy things we do? For our stupidest behavior, we blame bad genes and peer pressure; for the deeds we want to own, we credit a steely sense of purpose or even divine guidance. But a disturbing new force is emerging as a remote driver of our behavior: parasites. A recent story in The Atlantic lays out the chilling case that a microbe called Toxoplasma gondii has infested the brains of as many as 20 percent of Americans (and 55 percent of French people), refashioning neural connections to make us more fearless, more prone to schizophrenia, and—not incidentally—better disposed to cats, in whose guts the parasites reproduce. Other evidence suggests that people harboring the flu virus are more sociable—not because they want to infect their friends, but because the virus wants to spread. And now we’ve learned that the presence of parasites causes fruit flies to binge on alcohol (see Health & Science), and may have something to do with our own species’s propensity to drink too much.

The idea that the evolutionary drive of microbes can trump the human will is deeply depressing. Was that Winston Churchill standing up for Western civilization, or just parasites he caught from his ginger tabby, Jock? I say we just can’t go there. We have to draw a line in the cerebrum and lay claim to our own fates. “My parasites made me do it” is an even lamer excuse for foolishness than “I’m having a bad day.” So I hereby declare responsibility not only for my own actions, but for those of my entire biosystem. I urge you and all humanity to join me. Or should I say us?