A trove of sophisticated stone tools recently dug up from a South African cliff suggests early modern humans developed complex cognitive ability anywhere from 6,000 to 10,000 years earlier than many scientists believe.

In a study published in the journal Nature, researchers said they had unearthed a large number of small stone blades going back some 71,000 years. The heat-treated blades appear to have been designed for tipping spears or arrows that could be used for hunting game.

Crucially, the discovery indicates that these ancestors had the cognitive ability to manipulate complex tools. In addition, they were able to pass on their inventions to future generations. That, in turn, suggests the use of sophisticated language....