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An international research team led by the University of Vienna and the Medical University of Vienna has used long-term demographic data from Japanese macaques—a monkey species within the family of Old World monkeys—to show that unlike humans, there is no maternal mortality in these primates linked to childbirth. The results of the study were recently published in the journal PNAS.

The evolution of large brains and associated large fetal heads are key factors linked to maternal mortality in primates during childbirth. For humans, the baby's large head in relation to the mother's narrow birth canal can lead to serious birth complications. In countries with poor medical care, up to 1.5% of mothers die in childbirth as a consequence of birth. Macaques have a similar pelvis-to-fetal head ratio to humans. However, it remains unknown whether they face similar birth complications and maternal mortality as humans.

Biologists and midwives from the University of Vienna, the Medical University of Vienna, the Konrad Lorenz Institute for Evolution and Cognition Research (Klosterneuburg) and Kyoto University (Japan) have now investigated whether this is the case. Their research was based on long-term demographic data of birth and death events collected from a semi-free-living Japanese macaque population housed at the Affenberg in Landskron, Carinthia, Austria.

During the 27-year study period, 281 infants were born to 112 female macaques. The semi-free environment at Affenberg offers scientists the opportunity to study the behavior and reproduction of Japanese macaques under near-natural conditions. Since 2019, the Affenberg has been affiliated with the University of Vienna (Department of Behavioural and Cognitive Biology).

A female Japanese macaque nursing her few weeks old infant. Japanese macaques give birth to their infants between spring and early summer and nurse it for seven months to a year. After about a month, the infants begin to eat additional solid food. By winter, they are strong enough to survive the cold months. Credit: Angela Stojan

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