Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 119, Issue 16, Pages -Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.2114935119
Keywords
obstetrical dilemma; shoulder dystocia; ontogenetic allometry; childbirth
Categories
Funding
- Cooperative Research Program at KUPRI [2015-A-22, 2018-C-8, 2019-C-15, 2020-B-26]
- Japan Society for the Promotion of Science KAKENHI [17K07585]
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Obstetrical difficulties in humans arise from the large head and broad shoulders of the neonate relative to the maternal birth canal. The developmental features of the shoulders in humans likely evolved to ease obstetrical difficulties such as shoulder dystocia.
In humans, obstetrical difficulties arise from the large head and broad shoulders of the neonate relative to the maternal birth canal. Various characteristics of human cranial development, such as the relatively small head of neonates compared with adults and the delayed fusion of the metopic suture, have been suggested to reflect developmental adaptations to obstetrical constraints. On the other hand, it remains unknown whether the shoulders of humans also exhibit developmental features reflecting obstetrical adaptation. Here we address this question by tracking the development of shoulder width from fetal to adult stages in humans, chimpanzees, and Japanese macaques. Compared with nonhuman primates, shoulder development in humans follows a different trajectory, exhibiting reduced growth relative to trunk length before birth and enhanced growth after birth. This indicates that the perinatal developmental characteristics of the shoulders likely evolved to ease obstetrical difficulties such as shoulder dystocia in humans.
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