https://doi.org/10.36866/pn.75.30

Every parent is familiar with the feelings experienced when a child throws a public tantrum, and all too often the presence of scowling, disapproving strangers leads them to give in to the outburst. A new study of rhesus monkeys provides the first evidence that a similar effect is seen among our primate cousins (Semple et al. 2009). Bystanders affect the outcome of mother–infant interations in rhesus macaques. Proc Biol Soc 276, 2257–2262).

Rhesus mothers are much more likely to give in to their offspring’s tantrums when there are potentially aggressive animals nearby. Indeed, it appears that it is the threat of violence from these nearby animals that tips the balance in favour of the screaming infants, and forces mothers to acquiesce to their demands.

Stuart Semple of Roehampton University and his colleagues made these new discoveries while studying a population of rhesus monkeys living on Cayo Santiago, an island off the coast of Puerto Rico. The crying of rhesus monkey infants – just like that of human babies – is high pitched, grating and unrelenting.

While these cries are directed at mothers, nearby animals share the pain, and these onlookers often resort to violence to bring the earache to an end. Semple and his team found that both mothers and infants were over 30 times more likely to receive aggression during crying bouts than when infants were silent. Perhaps as a result of this threat, mothers are more than twice as likely to give in to their bawling babies when there were animals nearby that could turn nasty.

The study also found that mothers are prone to losing their cool when faced with screaming infants on one side and irritated onlookers on the other: mothers are over 400 times more likely to be aggressive to their infants when they are crying than when they are quiet.