Measurement of their strength, height and weight had been taken. Students were also asked to answer a questionnaire to estimate their aggression levels and give the number of fights they had had over the previous year.

Then volunteers were played randomized recordings and asked to measure the strength and formidability of the subjects, based on their expression. Another group gave their estimates based on images of subjects’ faces or bodies for comparison.

The voice-based experiments were not only accurate, but also listeners were able to find cues not available for viewers, researchers report in the Proceedings of the Royal Society B. A man’s voice gives better idea of how strong he is than his face does, but lags behind the image of his body.

Female voices carry significant information on their strength too, researchers say. However accuracy of the estimate was half as many for the 80 female subjects recorded for the experiment.

The cues hidden in the voice do not depend on self-perception. Neither do they depend on culture, since listeners estimated the strength of the Bolivians and Argentineans just as well as the strength of fellow Americans or Romanians.