Genetic Study Links Pelvic Morphology to Locomotion and Childbirth Outcomes

A combined study on human pelvic morphology, utilizing genetics and deep learning with data from over 31,000 individuals, reveals genetic links between pelvic structure and function, locomotion, and childbirth outcomes. Researchers from Western Washington University, Columbia University, and the University of Texas at Austin reported these findings in 'Science'. The study offers new insights into how our species evolved to balance the conflicting demands of bipedalism [walking on two legs] and childbirth. The transition to bipedalism in hominids [early human ancestors] led to significant changes in pelvic morphology, including a shorter and wider pelvis, facilitating an upright posture and efficient locomotion. However, this adaptation also presented a challenge for childbirth, as the narrowing of the birth canal made it more difficult for babies with larger brains to pass through. This conflict, known as the "obstetric dilemma" [the evolutionary challenge of balancing bipedalism with childbirth], has been debated for decades. It has been suggested that this dilemma might have been alleviated by evolving to give birth to less developed babies, allowing them to pass through the birth canal more easily. However, this theory has been questioned by recent studies showing that human gestation [pregnancy] and newborn size are comparable to other primates of similar size. While functional genomic studies on gene expression and comparisons between great apes and humans have provided information on pelvic development, the genetic basis of pelvic morphology in humans remains largely unknown. To study the genetic basis of the human pelvis, Liaoyi Xu and colleagues used dual-energy X-ray absorptiometry (DXA) [a type of medical imaging] images of the whole body and genetic data from 42,284 individuals in the UK Biobank [a large-scale biomedical database]. Using a deep learning approach on 39,469 high-quality DXA images, the researchers derived a comprehensive set of 7 skeletal measurements of the human pelvis and performed genome-wide scans to identify genetic loci [specific locations of genes on chromosomes] associated with variations in pelvic proportion. The researchers discovered 180 independent genetic loci associated with pelvic shape and found sex-specific differences in genetic architecture, as well as asymmetries in pelvic structure related to laterality [preference for using one side of the body]. They also found that wider birth canals are genetically associated with slower gait [manner of walking] and a higher risk of pelvic floor disorders, as well as a lower risk of obstructed labor [when a baby cannot pass through the birth canal]. Furthermore, the study found no evidence that shorter gestation evolved to facilitate childbirth, but did observe genetic correlations between pelvic shape and head size, suggesting evolutionary responses to the challenges of birthing babies with large brains.