At some point in evolutionary history, our ancestors came to understand, as no animal does, that death brings to an end a person’s bodily and mental presence in the world. But a potentially devastating consequence was that individuals, when experiencing physical or mental pain, might deliberately choose this outcome for themselves. Suicide has in fact become an alarmingly common trait, responsible for more deaths today than war and homicide combined. In this talk I shall ask what this means for human biological fitness. While some suicides are arguably adaptive, the majority are clearly maladaptive. Nonetheless the trait has been able to take hold because the suicide meme – to which humans have no natural immunity – easily infects vulnerable minds and is highly contagious.