Researchers of the University of Aix-Marseille, France, trained six captive Guinea baboons (Papio papio) to look at letters on computer screens. Sometimes the baboons were shown a real, four-letter English word, but on other trials they were shown a four-letter non-word. They had to press one of two buttons, depending on whether a word or non-word was shown, and were rewarded with food if they got it right.

After a month and a half, the baboons had learned dozens of words: one could reliably identify 308. That is an impressive feat of memory, but is not that surprising. Most complex animals can learn to categorise objects into two groups, given enough training. But the baboons became much better at identifying real words that they had never seen before. That means they had learned the rules that determine which letter orderings form real words, and could apply these rules to distinguish them from unlikely letter orderings.

The findings suggest that the brain mechanisms human children use when they learn to recognise written words are evolutionarily ancient, and were co-opted when written language came along, around 6000 years ago.