A cave on the southern coast of South Africa contains a bowl’s worth of edible shellfish dating back to about 165,000 years ago. Besides pushing back the earliest known seafood meal by 40,000 years, the discovery also marks the earliest time when people might have engaged in symbolic thought.

Anatomically modern humans probably emerged between 150,000 and 200,000 years ago in eastern Africa. When those humans first developed the potential for symbolic thought, including language, has remained a puzzle.

Looking for early human remains, Curtis W. Marean of the Institute of Human Origins at Arizona State University and his colleagues homed in on the caves at South Africa’s Pinnacle Point. In addition to discovering the first known seafood dinner—mostly brown mussels—they found small stone blades and reddish rocks tossed in with the shells. They identified a dozen or so pieces of iron-rich hematite rock with flattened sides bearing parallel grooves, indicating that the shellfish eaters scraped the rocks to make powder. Mixing that powder with sap or another binder yields a reddish or pinkish paint, possibly to adorn the body or the face.

That people were working with pigments back then “is a pretty good indicator of symbolic thought,” says Marean, who published the findings in the October 18 Nature. A population living on shellfish would have stayed in one place and grown in number, he notes, increasing the need for negotiations between individuals or social groups, which might have led to a system of decorative markings.