Is it possible to count objects you can't see? If you've ever received a boxed gift, or a mysterious package from Amazon, you might have tried to lightly shake the box to try to guess its contents.

Some 60,000 years ago, in what is now western France, a Neanderthal picked up a chunk of hyena femur and a stone tool and began to work. When the task was complete, the bone bore nine notches that ...