Part of the puzzle comes from the fact that babies are, in other ways, sponges for new information, forming 700 new neural connections every second and wielding language-learning skills to make the most accomplished polyglot green with envy. The latest research suggests they begin training their minds before they’ve even left the womb.

But even as adults, information is lost over time if there’s no attempt to retain it. So one explanation is that infant amnesia is simply a result of the natural process of forgetting the things we experience throughout our lives.

An answer comes from the work of the 19th Century German psychologist Hermann Ebbinghaus, who conducted a series of pioneering experiments on himself to test the limits of human memory. To ensure his mind was a completely blank slate to begin with, he invented the “nonsense syllable” – a made-up word of random letters, such as “kag” or “slans” – and set to work memorising thousands of them.

His forgetting curve charts the disconcertingly rapid decline of our ability to recall the things we’ve learnt: left alone, our brains throw away half of all new material within an hour. By Day 30, we’ve retained about 2-3%.