Are Humans Evolving Through Caesarean Sections?

Bigger newborn babies, statistically speaking, have a better chance of survival than tiny ones. So long as they can get out of their mothers’ bodies safely, that is! A study in Proceedings of the National Academy of Sciences suggests that the modern practice of Caesarean section is rapidly altering human evolution. Ever bigger babies carrying genes for ever smaller pelvic bones can now survive, the authors say, leading to bigger babies and more moms with small pelvic dimensions in the human population.

An estimated three to six percent of newborns around the world cannot negotiate their way through the birth canal. This mismatch of baby’s head and mother’s pelvis is called fetopelvic disproportion, or cephalopelvic disproportion (CPD). Before the advent of safe obstetrical intervention through Caesarean section in the 20th century, CPD was often a death sentence for these babies and their mothers, and those who managed to be born with great difficulty often suffered severe damage.

Obstetrical Dilemma

“Without modern medical intervention such problems often were lethal and this is, from an evolutionary perspective, selection,” says University of Vienna theoretical biologist Philipp Mitteroecker, lead author of the study in PNAS. “Women with a very narrow pelvis would not have survived birth 100 years ago. They do now and pass on their genes encoding for a narrow pelvis to their daughters.”1

Why then, evolutionists wonder, in two million years of evolution, haven’t women’s pelvic proportions evolved to accommodate bigger babies? This conundrum is known as the “obstetrical dilemma.” As an obstetrician, I must say this dilemma is of more concern to those who think philosophically about human evolution than to those of us who have actually delivered babies.

This obstetrical dilemma pictures the human pelvis as an evolutionary compromise between the need for a narrower pelvis for efficient bipedal locomotion and the need for a wider pelvis to accommodate a large-brained newborn’s head. This way of explaining the shape of the typical human female pelvis is based on a worldview that denies God’s 6,000-year-old “very good” creation in favor of a belief that our ape-like ancestors evolved a human-like pelvis to help them walk upright 4 to 5 million years ago. Supposedly this bipedally optimized pelvis couldn’t accommodate too many adjustments once the proto-human brain began to grow bigger two million years ago.

What If? . . . We’ll Never Know

“Why is the rate of birth problems, in particular what we call fetopelvic disproportion—basically that the baby doesn't fit through the maternal birth canal—why is this rate so high?” Mitteroecker asks.2 If CPD is a long-standing problem, why didn’t babies get steadily smaller before modern obstetrical intervention was available? Attempting to answer these questions, Mitteroecker and colleagues devised a mathematical model weighing the likelihood of CPD persisting or increasing over time. They report that if something happens to decrease mortality for either big babies or mothers with a narrow pelvis, then the incidence of CPD would rise quickly through evolutionary selection pressures. And lo and behold, what has happened in the past two generations to preserve the lives of big newborns and moms that cannot accommodate their passage? Caesarean sections!

“One side of this selective force—namely the trend towards smaller babies—has vanished due to Caesarean sections,” Mitteroecker says.3 “Although the obstetric selection pressure has been relaxed, the directional selection on D [the degree of mismatch between baby’s heads and mother’s pelvises] may persist and induce an evolutionary change,” the authors write.4 Mitteroecker’s model predicts that, assuming CPD occurred in about 3% of deliveries in the bad old days, then Caesarean section to save these babies and mothers would lead to a 3.6% incidence of CPD in just a couple of generations.

Caesarean sections began to be common about two generations ago. Has the incidence of CPD risen in response?

Caesarean sections began to be common about two generations ago. Has the incidence of CPD risen in response? The authors freely admit that they do not know. They likewise admit that we will never know whether their prediction has come to pass or not because there are many reasons that the rate of Caesarean section has risen dramatically in past decades. With so many variables, the accuracy or inaccuracy of their claimed “evolutionary” effect on the human obstetrical population cannot be demonstrated. Furthermore, obstetrical literature does not generally support their claim that the incidence of CPD has—theoretically at least—risen.

The Human Pelvis—Compromise Between Bipedality and Braininess?

Well, what if this increase in CPD has happened, as Mitteroecker believes? Does that then mean the foundational evolutionary principles at the root of the obstetrical dilemma are correct? After all, apes, with their small skulls, deliver their newborns without a hitch. Did the human female pelvis evolve as a compromise between bipedal walking and increasing brain size? Not at all!

Despite the loose use of the word evolution and discussions of the evolutionary obstetrical dilemma, this study deals only with variations among humans, Homo sapiens. It shows mathematically how variations in the characteristics of a population can change in a short period of time through forces such as selection, in this case saving the lives of those who would be eliminated from the gene pool by natural selection. Variation within the human population reveals nothing about human evolution from non-human ancestors.

Nothing about his model has anything to do with human evolution from ape-like ancestors or the evolution of bipedality.

Mitteroecker’s study is nothing more than a statistical analysis of the expected effect of life-saving medical care on the obstetrically relevant demographics of modern humans. Nothing about his model has anything to do with human evolution from ape-like ancestors or the evolution of bipedality. In fact, the study’s authors freely admit what many other evolutionists have come to admit: there is no demonstrable advantage to a super narrow pelvis in bipedal locomotion. The narrower pelvis cannot be conclusively shown to improve the way we walk. (See “Tie of Human Pregnancy to Bipedality Becomes Extinct” to learn more about the demise of this iconic evolutionary claim.)

Furthermore, the authors grope unsuccessfully for some evolutionary advantage to the narrower variety of the female pelvis—some advantage to show why women with a narrow pelvis are still around after two million years of dying in childbirth every time a big-brained newborn came along. First, they correctly describe the importance of the angles and tilts of the human pelvis in holding female reproductive organs as well as the bladder, bowel, and their contents inside the body against the urgencies imposed by gravity. Then they note that some studies have found that women with a narrower pelvis are better able to defy the age-associated downward drag of gravity on pelvic organs, a problem that occurs more commonly in women who have borne children. But they are unable to show how this happy advantage could contribute to such a woman’s ability to safely deliver a child in her youth, thus keeping those narrow pelvic genes in the gene pool.5

The Human Pelvis—Best for Babies

The human pelvis, in addition to providing attachments for ligaments and muscles that support the pelvic organs and help us control our bodily functions, is like a curved bowl that changes the angle of its tilt from top to bottom. As the pelvis cradles our internal organs, its top opening is at a 60-degree tilt. The bowl’s opening is almost horizontal by the time the pressure of these organs reaches its outlet, however. This is a bony arrangement we are thankful to have when the ravages of gravity and time in a sin-cursed world begin to weigh on our softer support structures.

While the authors mention this helpful aspect of pelvic design, they miss the whole point of the human female pelvic design, from an obstetrical point of view. There is no obstetrical dilemma! The anatomy of the pelvis, instead of making human labor difficult, provides an ideal exit route. The shape of the bony pelvis and the positioning of the pelvic muscles are such that the baby being propelled through the birth canal tends to twist and turn in the directions most suited for a safe and successful exit. Multiple but limited options are often available, allowing adjustments for pelvic type and fetal size.

The anatomy of the pelvis, instead of making human labor difficult, provides an ideal exit route.

Each option available for a baby’s journey turns the baby’s head so that its smallest dimension enters the curvy birth canal as it descends to each level. The infant’s head, having entered the pelvis looking sideways, must spin 90 degrees as the neck flexes and the head descends. This rotation must then reverse while extending the neck backwards as the baby descends farther into the pelvis. The pelvic shape forces the baby to finally twist as the head emerges to allow the roomiest possibility for the delivery of the shoulders, a challenging hurdle for particularly large newborns.

There are four human female pelvic types. The prevalence of each varies with ethnicity and even with maternal age. And while CPD can occur in any of these when there is sufficient mismatch between a baby’s size and a mother’s pelvis, women have been delivering their babies through all four pelvic variations for millennia. That babies can follow these geometric principles to negotiate each sort of pelvic variation is a testimony to the quality of God’s marvelous design for human childbirth, a design that normally guides a newborn’s large head safely through its dizzying path to the outside world. (Learn more in “The Evolution of Childbirth?”)

Medical Practices

What if a significant part of the C-section increase has been a side effect of saving women and babies who would have died miserably before? Mitteroecker says he isn’t against life-saving medical care, but warns of its consequences. He says, “Our intent is not to criticise medical intervention. But it’s had an evolutionary effect. The pressing question is what's going to happen in the future? I expect that this evolutionary trend will continue but perhaps only slightly and slowly. There are limits to that. So I don't expect that one day the majority of children will have to be born by [Caesarean] sections.”6

Indeed, despite all the absurd claims that medical science is rooted in evolutionary principles,7 we can be thankful that so far at least most people don’t long to let “survival of the fittest” take its natural course and, as Ebenezer Scrooge would urge, “decrease the surplus population.”8 We instead must wish that the Christ-like principles of compassion would more fully reign and eradicate the scourge of abortion and euthanasia that has polluted the medical practices of many.