Does the Childbirth Process Represent Clumsy Evolution or Good Engineering?
By Dr. Fazale Rana
Human beings have big heads to house large brains. Unfortunately, big heads make it difficult for infants to pass through the birth canal. This is called the obstetric dilemma.
Compared to all other animals, human birthing is long, painful, difficult, and dangerous. Globally, 3 to 6 percent of all births are obstructed, and 8 percent of maternal deaths during birth are caused by a mismatch in the infant’s head size and the mother’s pelvic opening. Because human brains are so large a significant amount of brain growth and development must take place after birth. Newborn brains are 25 percent the size of adult brains and one-year-old brains are about 50 percent. (A chimpanzee’s brain size grows from 40 percent the size of an adult’s to 80 percent in one year.)
Many evolutionary biologists view childbirth as an evolutionary “kludge job” that traces back to the emergence of bipedalism (as early as 6 million years ago). Knuckle-walking apes have a broad pelvis, rendering the birth canal larger than the infant’s head. Evolutionary biologists believe that as the first hominids evolved the ability to walk on two feet, their pelvis and birth canal narrowed to meet the biophysical demands of bipedalism.
This narrowing probably didn’t pose a big problem for the australopithecines, the first hominids that unequivocally possessed the ability to stand erect. Australopithecines had a relatively small brain size compared to humans and had fontanelles. openings in the neonatal skull that allow the frontal bones of the skull to slide past each other, compressing the infant’s head during passage through the birth canal. 1
Evolutionary biologists believe birthing became more difficult for larger-brained members of the genus Homo. It’s difficult to gauge the degree of difficulty experienced by Homo erectus and Neanderthals because paleoanthropologists have recovered few fossilized pelvic bones. Based on what fossils are available, paleoanthropologists think the birthing pattern of H. erectus and Neanderthals was distinct from modern humans’, but still might have been difficult. 2
Many biologists view the obstetric dilemma as a consequence of a historically contingent evolutionary process that settled on a barely workable design for human births. Accordingly, the anatomy of the common ancestor we shared with chimpanzees constrained the childbirth process. However, new research suggests childbirth might be more optimized than previously thought—findings in favor of viewing human birth as one of God’s good designs. 3
Pelvis Shape, Body Height, and Head Size
Researchers recently made use of a vast amount of data on the human pelvis—originally collected in the 1980s to help improve the design and safety of car seats—to understand the relationship between pelvis morphology and the demands of childbirth. They discovered a close association between pelvis shape, body height, and head size.
Women with larger heads give birth to children with larger heads and women with smaller heads to children with smaller heads. It turns out that women with larger heads also have a shorter sacrum. which provides extra room in the birth canal to accommodate a larger-headed infant. Researchers think that head size is genetically determined. Thus, head size and sacrum size are genetically linked traits. So, too, are body size and the shape of the birth canal. Shorter women have a smaller but rounder birth canal. Again, genes that control body height
appear to be linked to genes that control pelvis shape, consequently easing the obstetric dilemma.
As in australopithecines, the human obstetric dilemma is also alleviated by the presence of fontanelles. Particularly, humans’ anterior fontanelles remain for the first few years of life, allowing for a newborn’s massive growth in brain size. Eventually, new bone is laid down and the frontal bones fuse.
From a creation model perspective, these facts of genetics and anatomy demonstrate that human birthing is optimally designed to balance the trade-offs that arise from the competing demands of bipedalism and a large brain size. All engineers know complex designs often face trade-offs. Some components must be suboptimal in order to achieve maximum overall performance. Any attempt to maximize performance in one area (large brain size, for example) will degrade performance in others (as in birthing). Engineers must manage trade-offs carefully to achieve optimal performance for the system as a whole. I believe it is reasonable to see the birthing process in modern humans as an optimized system constrained by the demands of bipedalism.
A skeptic might ask why the Creator wouldn’t just design the human body so that bipedalism and large brain size don’t conflict. This is a fair question, but, again, trade-offs are inevitable for complex, multi-objective systems. It might be possible to conceive of a design for humans in which large brain size and bipedalism aren’t competing objectives, but that alternative would most certainly face trade-offs of another sort. It should also be noted that a biblical perspective of humanity would expect a difficult childbirth process. Genesis 3 tells us that as part of the curse God put on fallen humanity, He increased women’s struggles with childbirth.
While evolutionary biologists regard childbirth as a kludge job, support for the design view can be found in the ideas of Sir Richard Owen, a preeminent biologist who preceded Darwin. In Owen’s day the chief debate among biologists centered on function versus form. Some asserted that functional considerations were the most important principle for understanding organisms’ features. Others maintained that form (or architecture) of the organism was key.
Owen sought to unite these camps. He developed a sophisticated model that accounted for shared features in organisms as manifestations of an archetype that existed in the Mind of the First Cause. Whereas Darwin argued that shared features resulted from common descent, Owen asserted that they reflected common design. In Owen’s mind, the archetype represented teleology of a higher order:
The satisfaction felt by the rightly constituted mind must ever be great in recognizing the fitness of parts for their appropriate function; but when this fitness is gained as in the great-toe of the foot of man and the ostrich, by a structure which at the same time betokens harmonious concord with a common type, the prescient operations of the One Cause of all organization becomes strikingly manifested to our limited intelligence. 4
In light of Owen’s ideas, the design and physiological processes of the human body are a derivative of the vertebrate archetype, modified and optimized (to balance unavoidable trade-offs) to create large-brained, bipedal primates. The fact that the vertebrate archetype can be adapted to support so many distinct functions is a testament to its elegant design.
Subjects: Human Origins and the BibleSource: www.reasons.org