We like to think that we are masters of our own fates. The thought that others might be instead controlling our actions makes us uneasy. We rail against nanny states, we react badly to media hype and we are appalled at the idea of brainwashing. But words and images are not the only things that can affect our brains and thoughts. Other animals – parasites – can do this too. According to research by Kevin Lafferty from the University of California, Santa Barbara, a common brain parasite, Toxoplasma gondii, could be influencing human culture across the globe.

Humans can also contract the parasite, through contact with soil contaminated by the faeces of carriers or through eating infected meat. But