Squatting, pelvic morphology and a reconsideration of childbirth difficulties

Abstract

Childbirth is commonly viewed as difficult in human females, encompassed by the “Obstetrical Dilemma” (OD) described by early palaeoanthropologists as an evolved trade-off between a narrow pelvis necessitated by bipedalism and a large-brained fetal head. The OD has been challenged on several grounds. We add to these challenges by suggesting humans likely squatted regularly during routine tasks prior to the advent of farming societies and use of seats. We suggest that habitual squatting, together with taller stature and better nutrition of ancestral hunter-gatherers compared with later Neolithic and industrial counterparts, obviated an OD. Instead, difficulties with parturition may have arisen much later in our history, accompanying permanent settlements, poorer nutrition, greater infectious disease loads and negligible squatting in daily life. We discuss bioarchaeological and contemporary data that support these viewpoints, suggest ways in which this hypothesis might be tested further, and consider its implications for obstetrical practice. Lay Summary Human childbirth is viewed as universally difficult. Evidence from physical therapies/engineering, and studies of living and ancestral humans illustrates habitual squatting widens the pelvis and could improve childbirth outcomes. Obstetrical difficulties emerged late in prehistory accompanying settled agriculture, poorer nutrition and less squatting. Specific physical exercises could improve obstetrical practice.

There is an obstetrical dilemma: Misconceptions about the evolution of human childbirth and pelvic form

“…Moreover, greater pelvic breadth in females has been shown to yield additional speed flexibility and greater stride length, partly compensating for elevated locomotor costs owing to lower hip mechanical advantage (Gruss et al, 2017; Rak, 1991; Wall‐Scheffler, 2022; Wall‐Scheffler & Myers, 2017; Whitcome et al, 2017). These results led several authors to reject the hypothesis that efficient bipedal locomotion has restricted the evolution of a more spacious birth canal (e.g., Dunsworth, 2016, 2018; Warrener et al, 2015, Warrener, 2018; Gorman et al, 2022). Some authors questioned (Nowell & Kurki, 2020; Warrener et al, 2015) or even rejected (e.g., Dunsworth, 2018, 2021; Gorman et al, 2022) the entire notion of an evolutionary tradeoff subsumed under the classic obstetrical dilemma hypothesis.…”

“…These results led several authors to reject the hypothesis that efficient bipedal locomotion has restricted the evolution of a more spacious birth canal (e.g., Dunsworth, 2016, 2018; Warrener et al, 2015, Warrener, 2018; Gorman et al, 2022). Some authors questioned (Nowell & Kurki, 2020; Warrener et al, 2015) or even rejected (e.g., Dunsworth, 2018, 2021; Gorman et al, 2022) the entire notion of an evolutionary tradeoff subsumed under the classic obstetrical dilemma hypothesis.…”

“…In part, this stems from the motivation to combat the increasing pathologization and overmedicalization of childbirth in some industrialized countries and to draw attention to sociocultural, economic, and political factors underlying global maternal and neonatal mortality. Several authors have argued that there is no obstetrical dilemma at all, and emphasized that the difficulty of childbirth in modern societies is amplified by inappropriate obstetric practices, such as disadvantageous birth positions, patriarchal cultural and medical systems, as well as lifestyles that increase the risk of obstructed labor (e.g., Dunsworth, 2018 ; Gorman et al, 2022 ; Stone, 2016 ; Walrath, 2017 ). The fact that lifestyle and obstetric practices indeed affect parturition, along with the failure of some studies to identify biomechanical and metabolic constraints on pelvic dimensions (Vidal‐Cordasco et al, 2017 ; Warrener et al, 2015 ), has sometimes been interpreted as empirical support for discarding evolutionary explanations altogether.…”

Evaluation of Cannulated Compression Headless Screw (CCHS) as an alternative implant in comparison to standard S1-S2 screw fixation of the posterior pelvis ring: a biomechanical study

“…It is known that the SI joint has a physiological movement from 2 mm to 4 mm [ 32 – 34 ]. The fully threaded screws in group FT could have provided an overly rigid structure impeding the physiological movement of the SI joint.…”

The genetic architecture and evolutionary consequences of the human pelvic form

“…Some studies have found there is an association between the two ( 7 , 18 ), while others have not ( 19 – 22 ). Another point of debate revolves around whether differential birth canal proportions are associated with obstruction during delivery ( 7 – 14 , 17 , 23 – 26 ). Recently, there has been growing appreciation for the concept of a multifactorial pelvis, which proposes that the role of pelvic width reduction is not just to enable bipedal locomotion, but also to reduce the risk of pelvic floor disorders.…”