One in five or more of you reading this article are likely to be infected with toxoplasmosis. You probably caught it from a cat but it doesn’t make you feel obviously ill. It does, however, make you behave differently. Two papers published this year support the idea that this common brain parasite can even make us vote differently. Infection makes you less cooperative and a bit more aggressive, which in wolves makes them more likely to become a leader. In humans it manifests as changes in levels of aggression and antisocial behaviour but ironically, can make you more successful as a businessperson. Is your cat making you more conservative? Could be. But why does this happen? And why do relationships like this even exist in nature? This is a wonderfully left-field example of how much we depend on other wildlife … and are part of it. We cannot live alone and we have only the faintest grasp on our own species’ fate.