@article {333789,
	title = {Comparative primate analysis shows that humans are not unique in having a tight cephalopelvic fit at birth},
	journal = {Nature Ecology \&amp; Evolution},
	year = {2026},
	month = {2026/06/29},
	abstract = {<p>Human childbirth is regarded as uniquely difficult among primates, due to a tight cephalopelvic fit thought to result from an evolutionary trade-off between adaptations to bipedal locomotion and increasing brain size. This impression, however, may be an artefact of past adoption of anthropocentric measurements that underestimate birth challenges in non-human primates. Here we re-evaluate cephalopelvic proportions using species-specific three-dimensional data of the pelvic inlet along with neonatal cranial dimensions from a broad sample of extant primates. Results reveal that maternal body size is a key factor to consider. A tight cephalopelvic fit occurs in species with proportionately larger neonates, smaller pelves or a combination of both. The latter is the case in humans, producing the tightest fit among extant apes, but a similar combination of factors explains much more extreme cephalopelvic proportions in other species. Our findings reveal a diversity of obstetrical dilemmas across primates.</p>
},
	isbn = {2397-334X},
	doi = {http://dx.doi.org/10.1038/s41559-026-03102-5},
	url = {https://www.nature.com/articles/s41559-026-03102-5},
	author = {Torres-Tamayo, Nicole and Schlager, Stefan and Hirasaki, Eishi and Smith, Tim D. and Rae, Todd C. and Betti, Lia}
}
