Since the intelligence test was invented more than 100 years ago, our IQ scores have been steadily increasing. Even the average person today would have been considered a genius compared to someone born in 1919 – a phenomenon known as the Flynn effect.

We may have to enjoy it while we can. The most recent evidence suggests that this trend may now be slowing. It may even be reversing, meaning that we have already passed the summit of human intellectual potential.

Can we have really reached peak intelligence? And if that is the case, what can the subsequent decline mean for the future of humanity?