In 2010, a team led by Fredrick Kyalo Manthi of the National Museums of Kenya discovered an intriguing bone in the north of the country. Carol Ward of the University of Missouri and colleagues identified it as a third metacarpal, the long bone in the palm between the middle finger and the wrist.

Like modern human metacarpals, it has a small lump at its base – the styloid. This projection helps stabilise the wrist when the hand is gripping small objects between the thumb and fingers. Isotope dating revealed the bone to be about 1.4 million years old. It is likely to have belonged to Homo erectus.

Hand bones of early Homo erectus are almost unknown, says Richard Potts of the Smithsonian Institution in Washington, DC. “Having such a well-preserved specimen begins to answer questions about hand evolution,” he says.

“This is an exciting find,” agrees Mary Marzke of Arizona State University in Tempe. It shows that our ancestors’ hands were already evolving into their modern form 1.4 million years ago. The forceful, repetitive and sustained processes of tool use, such as digging with rocks, would have made stronger hands desirable, says Marzke.