Monkeys who observe fights tend to exploit the losers for grooming favours. This may provide an evolutionary context for our fascination with violence.

Researchers found that bystanders macaques who observed a fight were the most likely to initiate grooming with the loser and receive significantly more grooming than they provided the victims. Some monkeys even provoked fights with the aim of obtaining grooming favours.

This provides the bystander monkeys with a selection advantage, as more grooming leads to better physical condition and health.