The purpose of the experiment is to understand what goes on in a baboon’s mind, in this case how carefully the animals keep track of transient relationships.

Dorothy Cheney and Robert Seyfarth, a husband-and-wife team of biologists at the University of Pennsylvania, have spent 14 years observing Moremi baboons. Through ingenious playback experiments performed by themselves and colleagues, the researchers say they have worked out many aspects of what baboons use their minds for, along with their limitations.

Reading a baboon’s mind affords an excellent grasp of the dynamics of baboon society. But more than that, it bears on the evolution of the human mind and the nature of human existence. As Darwin jotted down in a notebook of 1838, “He who understands baboon would do more towards metaphysics than Locke.”