Male bonobos are less aggressive and receive life-long support from their mothers

High levels of a key thyroid hormone may be the reason bonobos are peaceful creatures, scientists have found. Despite the fact that chimpanzees and bonobos share similar starting conditions at birth, they develop different behavioural patterns later in life.

Male bonobos are less aggressive, engage in lasting friendships with females and receive life-long support from their mothers. In contrast, the social network of male chimpanzees consists of a mixture of male-male cooperation and aggressive behavioural strategies in males that aim at gaining and maintaining high social status.

Scientists from the Max Planck Institute for Evolutionary Anthropology have found that bonobos retain elevated thyroid hormone concentrations well into adulthood, whereas in humans and chimpanzees thyroid hormone concentrations decline after puberty. The late decline of thyroid hormones in bonobos might have consequences on their behaviour and might also indicate a delayed development of their mental capacities. Triiodothyronine (T3) is a hormone in the thyroid gland which is crucial for development in all vertebrates.

For their study, researchers took urine samples from around 200 zoo-living individuals ranging between one and 56 years of age. Hormone measures showed that the thyroid hormone pattern of western modern humans and chimpanzees was very similar, with high levels before puberty and a decrease of this hormone during and after puberty.

The samples of bonobos differed: the concentration of T3 remained high well until adulthood. “Our study showed that male bonobos, who are known for their low levels for aggressive behaviour, had higher thyroid hormone levels than females,” said Verena Behringer of the Max Planck Institute. “High thyroid hormone levels likely reduce aggression in male apes.”