Variation in obstetric dimensions of the human bony pelvis in relation to age‐at‐death and latitude

Abstract

We found narrower obstetrical dimensions in the female pelvis among individuals who died at younger ages. However, statistically equivalent variances in the two female age-at-death groups does not support natural selection on pelvic dimensions as leading to younger ages at death. We instead argue that this difference is result of continued growth due to remodeling in the pelvis occurring in females, but not males, after early adulthood.

Obstetric dimensions of the female pelvis are less integrated than locomotor dimensions and show protective scaling patterns: Implications for the obstetrical dilemma

“…Critics argue that the notion of a uniform human OD across populations fails to satisfactorily explain the relationship between difficult childbirth today and the way the human female pelvis evolved (Dunsworth, Warrener, Deacon, Ellison, & Pontzer, 2012; Gruss, Gruss, & Schmitt, 2017; Rosenberg & Trevathan, 1995; Wall‐Scheffler & Myers, 2017; Walrath, 2003; Warrener, 2017; Warrener, Lewton, Pontzer, & Lieberman, 2015; Wells, DeSilva, & Stock, 2012; Whitcome, Miller, & Burns, 2017). Further, wide variation in pelvic dimensions exists across populations (reviewed in Betti, 2017; Betti & Manica, 2018), and is influenced by many factors (Auerbach, King, Campbell, Campbell, & Sylvester, 2018; Betti, 2017; Betti, von Cramon‐Taubadel, Manica, & Lycett, 2014). Indeed, instead of being a static problem brought about during our evolutionary history, the OD may change with ecological factors such as growth during development and current nutritional status (Wells, 2015; Wells et al, 2012; Wells, Wibaek, & Poullas, 2018).…”

Assessing the role of the pelvic canal in supporting the gut in humans

“…We would like to note that the R 2 values indicate that gut size variation explains at most 25% of male canal variation and 24% of female canal variation ( Table 4 ). The discussion that follows below does not seek to minimize the influence of physiology, birth, and genetic drift on the pelvic canal [ 35 – 38 ], but rather describes the ways that gut size could add to the complexity of variation in the canal.…”

“…While our study aligns with the findings from other researchers that indicate that the pelvis also evolved as bony support for the pelvic floor and abdominopelvic organs [ 3 , 17 , 18 , 40 , 44 ], we want to highlight that this may only be one factor that influences the evolution and variation in the pelvic canal. Obstetrics, climate, ecology, physiology, and population history likely play important roles in shaping the pelvis [ 13 – 16 , 35 , 37 , 38 , 45 – 49 ]. The size of the birth canal, for example, seems to be conserved in female pelves from large- and small-bodied populations, indicating obstetrical demands remain important [ 49 ].…”

The association of parturition scars and pelvic shape: A geometric morphometric study

“…Bone is continually remodeled during life, and the female pelvis has been shown to change in shape throughout the reproductive period (Auerbach et al, 2018; Huseynov et al, 2016; Mitteroecker & Fischer, 2016). Likewise, the expression of pelvic features tends to increase with age (Bergfelder & Herrmann, 1978; Cox, 1989; Maass, 2012).…”

“…In the twenties and thirties, the female pelvis becomes wider and more gynecoid, which facilitates childbirth. After menopause, the female pelvis remodels toward a more android pelvis (Auerbach et al, 2018; Huseynov et al, 2016; Mitteroecker & Fischer, 2016). These shape changes are likely to be related to hormones and sex‐biased gene expression (Mitteroecker & Fischer, 2016; Parsch & Ellegren, 2013; Williams & Carroll, 2009), but also stature and body mass is related to pelvic shape (Fischer & Mitteroecker, 2017; Ruff, 2000).…”