Unintelligent Design - The Human Curved Birth Canal and Foetal Welfare

Relationship between pelvic depth (i.e. AP length of the pelvis) and spinal curvature as documented in the orthopaedic literature. The pelvis and spine are shown schematically in sagittal view. A Normal spinopelvic relationship where the centre of mass (indicated by the vertical dashed line through the last cervical vertebra, the so-called C7 plumbline) is positioned sagittally above both the hip joints and the superior endplate of the sacrum. B In an anteroposteriorly elongated pelvis (as indicated by the red double arrow) without spinal adjustment, the centre of mass is located behind the hip joints, which compromises the structural stability of upright posture. C To bring the centre of mass back above the hip joints in this elongated pelvis, the sacrum needs to be tilted forward. This leads to an overall increased curvature of the spine, particularly an increased lumbar lordosis and a deviation of the centre of mass from the sacral endplate. Increased lumbar lordosis is associated with multiple orthopaedic disorders, such as spondylolisthesis and disc herniation

Why do humans possess a twisted birth canal? | Universität Wien

A team led by Katya Stansfield from the University of Vienna has shown how the human birth canal evolved as a compromise and was not intelligently designed by an omniscient designer god to be the best solution to the design problem. In fact, it is a shoddy compromise made necessary because the basic human skeleton is an adaptation of the basic quadrupedal vertebrate skeleton and was never designed from the ground up for bipedalism as we would expect of a structure intelligently designed, rather than one evolved from earlier common ancestors with the other great apes and before that, a quadrupedal vertebrate with a horizontal spinal column.

One of the trade-offs was the welfare and survival of the foetus during the birth process. This was put at increased risk in order to ensure the long-term survival of the mother. Creationists might like to think about that as they try to force fit this into their religion with a putative designer god to whom all human life is sacred…

As the University of Vienna press release explains:

The relatively narrow human birth canal presumably evolved as a "compromise" between its abilities for parturition, support of the inner organs, and upright walking. But not only the size of the birth canal, also its complex, "twisted" shape is an evolutionary puzzle. Katya Stansfield from the University of Vienna and her co-authors have published a study in BMC Biology presenting new insights into why the human birth canal evolved to have this complex shape. They suggest that the longitudinally oval shape of the lower birth canal is beneficial for the stability of the pelvic floor muscles.

In most women, the upper part, or inlet, of the birth canal has a round or transversely (left-to-right) oval shape, which is considered ideal for parturition, but it is unknown why the lower part of the birth canal has a pronounced longitudinally (front-to-back) oval shape. This twisted shape typically requires the Baby to rotate when passing through the narrow birth canal, which further increases the risk of birth complications.

Rotational birth in humans. A The foetal head engages in a transverse to oblique direction and rotates about 90° to align its maximum dimension with the largest dimension of each pelvic plane. B Pelvic inlet, midplane and outlet in frontal view with parts of the pubic and ischial bones removed

In comparison with humans, apes have a relatively easy birth pattern that does not require rotation of the baby thanks to the longitudinally oval shape of the birth canal both at its inlet and the outlet. "For giving birth, it would be much easier to have a uniformly shaped birth canal also in our species", says Katya Stansfield, a specialist in biomechanics. Instead, the twisted human shape requires a complex, rotational birth mechanism: The baby needs to rotate to align the longest dimension of its head with the widest dimension of each plane of the birth canal. Misalignment can lead to obstructed labour and result in health risks for both mother and baby.

The research team of evolutionary biologists and engineers from the University of Vienna, the Konrad Lorenz Institute for Evolution and Cognition Research in Klosterneuburg and the University of Porto have shown that there was an evolutionary trade-off between ease of birth and the need for pelvic floor stability and balance due to adaptation to an upright posture. They have shown that the shape of the outlet is a compromise between the need for continence, sexual intercourse and stability with the welfare of the foetus during birth being compromised for the other competing design needs. The resulting shape means a greater pelvic tilt and a smaller lumbar spine curve could be avoided. A greater lumbar curve would have resulted in a weaker back because, again, the spinal column with its discs evolved out of one designed for a horizontal, quadrupedal posture.

In their open access paper published in BMC Biology, the authors say:

Abstract

Background
The human foetus typically needs to rotate when passing through the tight birth canal because of the complex shape of the pelvis. In most women, the upper part, or inlet, of the birth canal has a round or mediolaterally oval shape, which is considered ideal for parturition, but it is unknown why the lower part of the birth canal has a pronounced anteroposteriorly oval shape.

Results Here, we show that the shape of the lower birth canal affects the ability of the pelvic floor to resist the pressure exerted by the abdominal organs and the foetus. Based on a series of finite element analyses, we found that the highest deformation, stress, and strain occur in pelvic floors with a circular or mediolaterally oval shape, whereas an anteroposterior elongation increases pelvic floor stability.

Conclusions
This suggests that the anteroposterior oval outlet shape is an evolutionary adaptation for pelvic floor support. For the pelvic inlet, by contrast, it has long been assumed that the mediolateral dimension is constrained by the efficiency of upright locomotion. But we argue that the mediolateral elongation has evolved because of the limits on the anteroposterior diameter imposed by upright posture. We show that an anteroposteriorly deeper inlet would require greater pelvic tilt and lumbar lordosis, which compromises spine health and the stability of upright posture. These different requirements of the pelvic inlet and outlet likely have led to the complex shape of the pelvic canal and to the evolution of rotational birth characteristic of humans.

Stansfield, Ekaterina; Fischer, Barbara; Grunstra, Nicole D. S.; Pouca, Maria Villa; Mitteroecker, Philipp
The evolution of pelvic canal shape and rotational birth in humans
BMC Biology 19, 224 (2021). DOI: 10.1186/s12915-021-01150-w

Copyright: © 2021 The authors. Published by BioMed Central Ltd
Open access
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)

As an evolutionary process, as hominins evolved from earlier vertebrate ancestors, this is entirely understandable because evolution often results in a compromise as various competing factors are traded off against one another depending on their relative contribution to the overall fitness of the species.

As the intelligent design of an omniscient god who supposedly values all human life and especially that of the unborn foetus, this makes no sense whatsoever. Why would such a designer god start off with a skeleton for which so many compromises had to be made and why would it sacrifice the welfare of the unborn foetus in that compromise?

In fact, the human pelvis and the curved birth canal are examples of the sub-optimal, flawed utilitarian design found throughout the human body - flaws that belie the claim that humans were intelligently designed by an omniscient, omni-benevolent god to whom all human life is sacred.

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