Another Evolutionary Dogma Bites the Dust
We are exposing how easily institutional
science can mistake its own philosophical
commitments for verified empirical data
Inventing the Uniquely Human “Obstetrical Dilemma”
By John D. Wise, PhD
For over half a century, the public has been treated to a confident textbook narrative regarding human childbirth. It is called the “obstetrical dilemma.” When our evolutionary ancestors adopted the upright posture, natural selection narrowed the pelvis to accommodate bipedal locomotion. Later, as brains expanded, the human birth canal became a hazardous, agonizing bottleneck, saddling human mothers with a uniquely clumsy – and dangerous – evolutionary compromise, while our non-human primate cousins allegedly enjoyed spacious, effortless deliveries.
This neat little parable has been used to explain everything from the helplessness of human infants to the evolution of social midwifery (e.g., by Lucy Hyde). There is just one problem.
The narrative was built on a circular, human-centric illusion.
Comparative primate analysis shows that humans are not unique in having a tight cephalopelvic fit at birth (Nature Ecology & Evolution, 29 June 2026).
According to the study by researchers at University College London (UCL), the foundational data supporting this textbook dogma was fundamentally flawed.
Human childbirth is regarded as uniquely difficult among primates, due to a tight cephalopelvic fit thought to result from an evolutionary trade-off between adaptations to bipedal locomotion and increasing brain size. This impression, however, may be an artefact of past adoption of anthropocentric measurements that underestimate birth challenges in non-human primates.
For nearly eighty years, comparative anthropologists inherited a measurement convention that treated non-human primates as though their pelvic anatomy followed the same obstetric geometry as humans.
The Anatomy of Adolph Schultz
The myth of the carefree primate birth traces back to the 1940s, when primatologist Adolph H. Schultz published comparative investigations estimating the fit of a newborn head into the maternal birth canal. As the authors of the UCL study note:
This interpretation, and in particular the widely reproduced figure, was highly influential on subsequent work, effectively defining anthropological conceptualization of birth across primates, and reinforcing traditional assumptions that (1) human childbirth is uniquely difficult due to a tight cephalopelvic fit and a distinct pelvic canal shape, and (2) other primates face little to no birth obstruction… Later studies, accepting these assumptions without re-examination, sought to identify the evolutionary and anatomical factors that make human parturition particularly challenging. [emphasis mine]
But the UCL research team, led by Drs. Nicole Torres-Tamayo and Lia Betti, decided to actually look at the raw data using modern 3D skeletal modeling across 29 primate species.
What they found completely dismantles Schultz’s historical narrative.
Schultz committed a human-centric measurement error. In human anatomy, the tightest part of the birth canal is measured from the top ridge of the sacrum to the pubic bone. Schultz applied these same human landmarks to other primates. However, a monkey’s sacrum sits much higher relative to its pelvis. By using human points, Schultz drew a fictional, tilted plane that completely missed the actual skeletal bottleneck. As the authors write:
In non-human primates, the sacrum is positioned higher relative to the pubis … By applying standard human obstetric measurements to non-human primate anatomy, pelvic inlets are treated as idealized, generic ovals… misrepresenting cephalopelvic relationships in non-human primates and providing an unreliable basis for understanding the apparent uniqueness in human childbirth.
When the UCL team mapped the true rigid skeletal ring, non-human primate birth canals instantly shrank by an average of 11%, reaching more than an 18% reduction in some species.
Furthermore, evolutionary models assumed all primates are born like humans, crown-first. In reality, primates with pronounced snouts, like baboons and squirrel monkeys, almost always deliver face-first, with their necks fully extended. This changes the geometric orientation entirely, making the head height, rather than head length, the critical measurement.
Smaller Primates Have It Worse
When the researchers corrected these errors and applied realistic face-first dimensions, the myth of the “unique human dilemma” evaporated. While great apes like chimpanzees and gorillas do have spacious birth canals, humans are not the odd ones out in the wider primate world. In fact, under true geometric scaling (allometry), smaller primates face obstetric crises that make human childbirth look spacious:
Our results challenge the traditional perception of a uniquely tight cephalopelvic fit at human birth by showing more extreme CPP [cephalopelvic proportions] in several non-human primate species and a tighter fit in more taxa than previously recognized… While humans remain among the most constrained species of apes, the even tighter fits in several primates, such as galagos, squirrel monkeys and patas monkeys, indicate that birth constraints are not unique to our evolutionary lineage.
In small-bodied monkeys like tamarins and squirrel monkeys, the neonatal head is actually geometrically larger than the resting pelvic opening, yielding CPP scores of 1.87 and 1.92 – almost twice the size of the available space! These animals survive only because they possess dynamic design features that put “evolutionary trade-off” theories to shame. For example, the pelvic ligaments of squirrel monkeys relax so significantly during labor that their hipbones temporarily dislocate, expanding the birth canal area by up to 100%.
The Smoking Gun: “Never Been Assessed”
The paper does not disprove that bipedalism affects the human pelvis, but what the paper does explode is the dogmatic certainty with which the “unique human evolutionary penalty” was preached for generations without any comparative data to back it up.
In a stunning admission of institutional blind spots, the authors write:
To the best of our knowledge … the relationship between maternal body size and the two key components of CPP, pelvic inlet size and neonatal head size, has never been assessed.
Read that sentence again. For sixty-five years – ever since Sherwood Washburn officially coined the term “obstetrical dilemma” in 1960 – physical anthropology and evolutionary biology have treated this concept as an unquestioned, fundamental fact. Yet, the core mathematical engine of the entire theory was never checked across the primate order.
Researchers spent decades asking why humans possessed a unique evolutionary trade-off before first establishing whether that uniqueness actually existed. They repeatedly reproduced a simplified 1940s schematic, assumed the relationship was unique to humans, and started building their theoretical castles in the sky.
Unchecked Dogma: a Pattern?
The authors of this paper are acknowledging and exposing a profound pathology in the scientific enterprise. Human institutions possess an immense capacity for “paradigmatic amnesia.” A pioneer proposes a speculative, simplified model that satisfies the philosophical requirements of the current consensus. The model gets turned into a clean, compelling textbook diagram. Within a generation, the messy, unexamined caveats are completely forgotten, and the diagram hardens into a dogma.
We have seen this same pattern repeat across multiple disciplines:
- In Geology: For decades, the secular consensus confidently declared that the sharp, 90-degree folds in the Grand Canyon’s Tapeats Sandstone were formed by millions of years of “ductile flow” under deep heat and pressure. It preserved the preferred timeline, so it was taught as fact. Yet, when geologists finally examined the rocks under a thin-section microscope, they found no signs of metamorphic deformation. The geological establishment spent a century preaching a mechanism they had literally never verified under a microscope.
- In Geomorphology: For generations, textbooks and tour guides insisted that the Grand Canyon was the slow, gradual product of “a little bit of water and a lot of time,” and anyone suggesting rapid, catastrophic draining was dismissed out of hand. Yet a recent paper in Science analyzing the Bidahochi Formation concluded that the canyon was likely carved rapidly by a massive lake-spillover event, an idea proposed as early as 1934 but largely ignored for nearly a century because it conflicted with uniformitarian dogma.
- In Genetics: The insistence that 98% of the human genome was evolutionary “Junk DNA” actively stalled research for decades. Global projects like ENCODE have since revealed that this “junk” is actually a hyper-complex, four-dimensional control room packed with regulatory networks.
When we fairly and reasonably ask, therefore, “What else has never been checked?” we are exposing how easily institutional science can mistake its own philosophical commitments for verified empirical data. The UCL paper is a brilliant piece of corrected science, but it stands as a severe warning about the nature of consensus. A scientific community can dogmatically assert foundational concepts, preach them to the public for years, and contemptuously dismiss anyone who questions them, all the while overlooking, as here across the primate order, whether those foundational assumptions had ever been rigorously tested.
John Wise received his PhD in philosophy from the University of CA, Irvine in 2004. His dissertation was titled Sartre’s Phenomenological Ontology and the German Idealist Tradition. His area of specialization is 19th to early 20th century continental philosophy.
He tells the story of his 25-year odyssey from atheism to Christianity in the book, Through the Looking Glass: The Imploding of an Atheist Professor’s Worldview (available on Amazon). Since his return to Christ, his research interests include developing a Christian (YEC) philosophy of science and the integration of all human knowledge with God’s word.
He has taught philosophy for the University of CA, Irvine, East Stroudsburg University of PA, Grand Canyon University, American Intercontinental University, and Ashford University. He currently teaches online for the University of Arizona, Global Campus, and is a member of the Heterodox Academy. He and his wife Jenny are known online as The Christian Atheist with a podcast of that name, in addition to a YouTube channel: John and Jenny Wise.