Birth


around 1.5 million years later. Second, the increase in height and field of vision was especially useful for hunter-gatherers when foraging and hunting and for avoiding predation. Third, the upright posture meant that less of the body surface was directly exposed to the sun’s rays. The upright posture required additional muscularisation to maintain bowel and bladder continence, and naturally affected childbearing and birth, which in quadrupeds involved the foetus traversing a tubular-shaped birth canal. Foetuses of bipedal hominids were required to exit the womb through a deeper, curved tube necessitating the negotiation of three pelvic planes, which on the whole they successfully achieved. Around 500,000 years ago, encephalisation (skull and brain growth) took place, eventually giving rise to the modern hominidae.


Physical anthropologists have noted that early hominids were possibly more efficient at birthing because their offspring possessed proportionately smaller head to maternal pelvis ratios. However, Wittman and Wall contend that, while this gave distinct ecological and social advantages to humans over other species, in real terms the foetus became nearly twice as large in relation to maternal size when compared with other primates. They also note, however, that the relationship of cranial size to body size in the human neonate is proportionate to that of other primates.29


Thus, while there is less free space in the pelvis of modern woman at term, foetal head size generally remains compatible with maternal pelvic capacity and does not actually hamper long-term brain growth; this occurs rapidly with maternal nurturance, during a phase of ‘secondary altriciality’ in which the baby continues to mature after birth at an accelerated rate.29


Individual Natural Design?


The various bones of the female pelvis exhibit a range of individual features, accounting for slight variations in individual overall pelvic form. This renders Caldwell and Moloy’s attempts at pelvic classification in the 1930-40s problematic; their four main ‘parent’ pelvic types – gynaecoid, anthropoid, platypelloid and android – included a vast number of subclassifications.30,31,32


These researchers


found that the female pelvis tended to be wider than the male prototype, possibly influenced by hormonal activity in adolescence, providing advantages for women during childbirth; however, the ‘male types’ of pelvis could also be found in women and vice versa.


As Roy notes, dystocia appears to be unknown in wild animals. Interestingly, moderate symphysis pubis diastasis and pelvic joint separation is a normal feature of pregnancy and has recently become more widely recognised and noted in pregnant women. This allows for a small degree of pelvic expansion at the symphysis pubis and the sacroiliac joints during birth, the ‘disadvantage’ being that it sometimes leads to pelvic instability. Nonetheless, in normal cases, it slightly assists birth, especially when combined with moulding of the foetal skull.33


In some small rodents this process has


developed more fully; during pregnancy, the symphysis pubis softens to become a fibrous tissue, which stretches to permit the birth of relatively large offspring.34


The drivers of adaptations come in many guises and often involve certain compromises. Wiley considers sociopolitical forces to be equally powerful determinants of health and disease.35


For example, changes to the social environment since the advent of the printing 10


Evolution is concerned with survival of the fittest, as expressed in the ability of an organism to reproduce and transmit its genes. The major question that presents itself is: why do humans currently require so much medical assistance with birth? What has happened to the notions of adaptation and survival of the fittest, as propounded by Darwin and others? In contrast to the common perception of Homo sapiens as sitting at the apex of the evolutionary process, Steer contends that ‘it is better to see ourselves in transition from what we were to what we must become if we are not to follow many previous species to extinction’.6


Like all other species, we need the ability to


adapt in order to avoid facing extinction. Steer maintains that CS, if seen as a type of evolutionary adaptation, should perhaps become the norm; originally a medical solution to dystocia, it could become so safe that ‘for most women the unpredictable risks of labour will no longer be justified’. As Steer states, this would remove selection pressures limiting foetal size, and the average birth weight and head size would no longer be restricted by pelvic size, creating in time a situation in which Caesarean birth could become a necessity for all women. In his view, CS would in this way facilitate the continued development of human intelligence by allowing brain size to increase yet further. Steer here is assuming a positive correlation of brain size with intelligence, which does not accord with what is observed in


EUROPEAN OBSTETRICS & GYNAECOLOGY SUPPLEMENT


press have created the need for increased levels of close work and reading, which appear to have increased levels of myopia. Myopia in hunter-gatherer populations is a significant disadvantage, as it can expose affected individuals to danger, but is not in more developed societies, where spectacles and laser treatment are available.


The Caesarean Operation – An Evolutionary Advantage?


CS has become an increasingly common intervention in the developed world. In 1998, a professor of obstetrics, Philip Steer, in an article that discussed future birth trends and the impact of CS from an evolutionary perspective, put forward the rather contentious suggestion that CS should be seen as an advantageous form of adaptation. He wrote: ‘Rather than indulging in reflex pleas to “return to the simplicity of nature” (which is often “red in tooth and claw”), we should be concentrating on making caesarean section even safer, researching ways to predict labours that will have an adverse outcome, and listening to what (properly informed) women want’.6


Steer contends that whether or not the cost of CS is acceptable ‘depends on the value assigned to maternal autonomy in relation to convenience, avoidance of pain and damage to pelvic structures and her desire to protect her baby’.6


Here he appears to be reducing the issue to


one of a supposedly rational consumer choice, disregarding the fact that such a choice may be available to relatively few women if payment was involved. And, as the urogynaecologist Ingrid Nygaard contends, most women do not require urogynaecological surgery after a vaginal birth, and Caesarean delivery is not completely preventive of pelvic floor damage, which leads her to conclude that ‘advocating caesarean birth to decrease pelvic floor disorders is ill-advised’.36


Advocates of CS for


breech birth have couched this in terms of protecting the baby, which it undoubtedly is now that junior obstetricians and midwives have less opportunity to develop their clinical skills of vaginal breech birth. The matter of cost plays an important part in determining our future reproductive capacity, and possibly requires more careful consideration by the professions, politicians and the public. In 2011, a CS cost £2,369, whereas a vaginal birth cost £1,665.3


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