An international research team has used extensive demographic data on Japanese macaques, a species of Old World monkeys, to demonstrate that these primates do not experience maternal mortality associated with childbirth, unlike humans. The findings were recently published in the scientific journal PNAS.
This research collaboration, spearheaded by the University of Vienna and the Medical University of Vienna, utilized long-term demographic data from Japanese macaques to reveal the absence of maternal mortality linked to childbirth in these animals, contrasting sharply with the human experience. The study’s results were released in the scientific journal PNAS.
The development of larger brains and consequently larger fetal heads are significant factors that contribute to maternal mortality during childbirth in primates. For humans, the large head size of the baby relative to the mother’s narrower birth canal can result in severe complications. In regions with inadequate medical facilities, maternal death rates can reach up to 1.5% during childbirth. Interestingly, macaques exhibit a pelvic-to-fetal head ratio that is similar to humans. Nevertheless, it is still unclear whether they encounter comparable childbirth complications and maternal mortality rates like humans do.
A team comprising 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) sought to explore this question. Their investigation relied on long-term demographic data collected on births and deaths from a semi-free-ranging population of Japanese macaques at the Affenberg facility in Landskron, Carinthia, Austria. Over a span of 27 years, 281 infants were born to 112 female macaques at this site. The semi-natural environment at Affenberg allows researchers to observe the behavior and reproductive patterns of these monkeys in conditions that closely mimic their natural habitat. Since 2019, Affenberg has been associated with the University of Vienna’s Department of Behavioural and Cognitive Biology.
No maternal mortality in macaques
“Our findings indicate that none of the females in this population have died during childbirth over the past 27 years,” states midwife and evolutionary anthropologist Katharina Pink from the Department of Obstetrics and Feto-Maternal Medicine at the Medical University of Vienna, and co-first author of the study. This outcome reveals that Japanese macaques do not share the same maternal mortality risks as humans, despite having a comparable pelvic-to-head ratio.
The reason why childbirth seems less hazardous for macaques than for humans remains an unanswered question. The research team suggested potential explanations for this unexpected finding: “We hypothesize that the pelvic girdle and pelvic floor muscles of macaques have more flexibility during labor compared to those of humans, and that the dynamics of birth are not as constrained due to variations in pelvic structure,” explains Barbara Fischer, also co-first author and a researcher at the Department of Evolutionary Biology at the University of Vienna and the Konrad Lorenz Institute for Evolution and Cognition Research.
Intuitive birthing and freedom of movement
There are currently very few academic accounts of births among free-living, non-human primates. Most births occur during nighttime or early morning, making them challenging to observe. Documented birth events demonstrate that non-human primates often prefer to deliver while standing or squatting, which likely optimizes the inherent flexibility of their pelvis. “These observations could motivate future research to investigate how allowing freedom of movement during natural births can result in more individualized and less invasive care for mothers,” remarks midwife Katharina Pink.
