Pink KE, Fischer B, Huffman MA & Pflüger LS. 2024.
PNAS 121 (42) e2316189121, doi.org/10.1073/pnas.2316189121
Published online 7 October 2024

Significance

A tight fit between the neonatal head and maternal pelvic dimensions is often associated with an increased maternal mortality risk in humans and some other primate species. Japanese macaques show a human-like tight feto-pelvic fit. Based on 27 y of data from a continuously monitored semi-free-ranging group of Japanese macaques, we found no birth-associated maternal mortality in macaques, which differs from the situation in many human populations.</section><section id="abstract" property="abstract" typeof="Text" role="doc-abstract">

Abstract

Human fetuses at term are large relative to the dimensions of the maternal birth canal, implying that their birth can be associated with difficulties. The tight passage through the human birth canal can lead to devastating outcomes if birth becomes obstructed, including maternal and fetal death. Although macaques have to accommodate similarly large fetuses, relative to their maternal birth canals, it was not known whether macaque mothers face birth difficulties similar to humans. Based on 27 y of demographic data from a semi-free-ranging, closely monitored population of Japanese macaques (Macaca fuscata), we found no birth-associated mortality in macaques. This differs from the situation in many human populations. We suggest three nonmutually exclusive hypotheses to explain these observations. i) The macaque fetal skull is similarly flexible as the human fetal skull. ii) The macaque pelvis and connective tissue show greater flexibility during birth. iii) The interplay between macaque pelvic shape and birth dynamics is smoother and incurs fewer complications than in humans.</section>