Discussions and empirical tests of the obstetrical dilemma have long been dominated by the presumed negative effect of a wider (left-to-right) pelvis on bipedal walking. This study  shows exciting new findings that highlight that the evolution of human pelvic form is not all about birth and locomotion, and that pelvic canal dimensions other than width may also be under selective constraints in humans. 

Firstly, the authors have found a strong association between an increased risk of pelvic floor dysfunction (specifically prolapse) and mediolaterally wider birth canals. This lends further support to the pelvic floor hypothesis, which argues that the pelvic floor is particularly important in humans due to our upright posture and that a narrower birth canal has evolved to benefit pelvic floor health. 

Additionally, whereas most previous work has tested the obstetrical dilemma by focusing on pelvic width, this study showed that the anterior-posterior (belly-to-back) length or depth of the birth canal also impacts locomotion, and back pain. The latter could point to a relationship between the curvature of our bipedal spine and pelvic shape, which has been hypothesized but not yet tested. This study provides a further indication that this could be a fruitful new direction of evolutionary research.