Babies, Brains And The Pelvis: A Story Of Evolution

Caesarean-section deliveries are changing the way our bodies and brains are evolving. No, this is not sci-fi. It's the present.

ByAnand Ranganathan
Babies, Brains And The Pelvis: A Story Of Evolution
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Life has no purpose. We are a conspiracy hatched by thunder and lightning and water and ammonia and hydrogen and methane and dust, as demonstrated by Stanley Miller in 1953, the same year Watson and Crick discovered the structure of DNA and Elizabeth II became the queen of England. For both science and servility it was the dawn of a new era. But here’s the thing. Had Miller not been gifted Oparin’s book The Origin of Life as a birthday present, had Watson not sneaked a peak at Rosalind’s DNA diffraction plates, had Elizabeth’s uncle not abdicated the throne for his lover… .

Chance. That quirk of fate humans accept gladly, but squirm when told they, too, are its product. Amino-acetonitrile met water and formed an amino-acid four billion years ago; a sperm met an egg and produced a baby yesterday. All random, all Harry and Sally; need not have happened; very easily did not. Scientific certitude makes this sound obvious, but it wasn’t always. The trick was to connect the present to its past, to seamlessly link today’s world with the RNA world. Enter Charles Robert Darwin. Like Hubble, whose discovery of the red-shift allowed us to walk backwards till we stumbled on the moment of the Big Bang itself, the theory of evolution made us rationalise our own beginning, right back to the time of that chance creation simulated in a round-bottomed flask by Miller.

The theory of evolution is an axiom. Let religion and its mesmerising literature not fool you into believing you were created by someone who wasn’t a product of the RNA world in the first place. Genome-sequencing, sexual-PCR, ribozymes, and proto-cells provide irrefutable proof of a common origin of all life-forms and their subsequent branching-out because of Darwinian principles of survival and adaptation. Evolution governs our every breath, our every move; evolution is the reason why we live and why we die. Evolution, sadly, is also misunderstood. Many believe it has done its job, which was to perch man on the top of the biological pyramid. Nothing could be more wrong and nothing could be further from the truth. If at all, human evolution has speeded up and for once, science is to blame.

Life may not have a purpose, but science does – to make sense of our surroundings and, somewhat less esoterically, to make our lives more comfortable. In doing so, scientific intervention has the capacity to change the course of human evolution. The invention of tools and the formation of societies altering human anatomy, planned agriculture inducing lactose tolerance, are but two instances. Last week, one such intervention set the proverbial evolutionary barn on fire. Philipp Mitteroecker and colleagues, writing in the prestigious Proceedings of the National Academy of Sciences proposed that the Caesarean section is altering the course of human evolution by helping babies who would otherwise have succumbed to the painful process of childbirth, survive. The scientists say this evolutionary selection has resulted in an astonishing 10 to 20 per cent increase in the incidence of fetopelvic disproportion (a baby unable to pass through the birth canal).

To be sure, Mitteroecker and colleagues aren’t the first to suggest this and it is rather unbecoming of them to not cite the original exponent of this hypothesis. As far back as 2011, writing in The American Journal of Obstetrics and Gynaecology, Dr Joe Walsh had proposed an evolutionary fallout of the C-section. “The maternal pelvis can get smaller over time, and fetal birth-weight can get greater over time, because there is now nothing to limit these changes,” wrote Dr Walsh. To understand this hypothesis one needs to first comprehend the evolution of two of the most prominent anatomical features of a human body – brain and pelvis.

The human brain has evolved remarkably quickly. In a matter of 2.5 million years it has tripled in size. Scientists believe much of the new neural volume is utilised for requirements such as social cognition, empathy, language, and interaction skills. Indeed, the precise gene sets that determine the size of our brain have recently been identified; genes responsible for cognition feature prominently. Humans, incidentally, have one of the largest Encephalisation quotient, a metric to gauge brain to body-mass ratio. But with large brains comes the awkward problem of them having to pass through the constricted birth canal and a pelvis that – ask any screaming about-to-be-a-mother – appears hopelessly ill-designed for delivering a life-form. Not for nothing is the pain of childbirth considered a universal euphemism for indescribable agony. For men who have witnessed it, childbirth is unquestionably the most painful experience one can have without actual physical pain. It seems impossible until the baby’s wailing fills the operation theatre and you are left gaping at that enormous head having successfully made its way out.

Our brains have evolved to becoming enormous but what about the pelvis – has it kept pace with the rapidly altering size of the human brain? A widening of the pelvis, and consequently of the birth canal, would be a natural evolutionary response to the enlargement of the brain that has to pass through it. Also, one would have thought the advent of agriculture, a change in diet, sedentary lifestyle, and reproductive behaviour would contribute substantially towards a rapid evolution of the pelvis. Well, it is not so simple. The widening would cause havoc with our gait and bipedalism, not to mention severely affect heat dissipation, another crucial factor responsible for pelvic evolution. We are therefore stuck in a compromise, of which the implausible gymnastics performed by the baby just before it enters the world are a living proof. Childbirth is a miracle yes, but a miracle of evolution. And this evolution is happening in real-time.

Fifty years ago, roughly 30 babies in 1,000 found it physically impossible to emerge from the birth canal. Today, that figure stands at 36. Five per cent of all deliveries in the United States of America in 1970 were Caesarean. Today that figure is 33 per cent, three times of what the World Health Organisation considers the ideal rate. The world over, C-section is taking the form of an epidemic. Eighty-two per cent of all deliveries in private Brazilian hospitals are now Caesarean. India is no different. The Caesarean rate was 2.5 per cent 25 years ago, well below the WHO recommended 10 per cent. Today it is 15.4 per cent and snowballing rapidly. In the same time as India’s C-section rate jumped to 15.4 per cent, the global average rate did, too – from 6.7 to 19.1 per cent. For better or for worse, to satisfy astrological whims or minimise pain, of their own accord or through coercion, mothers are increasingly choosing Caesarean over natural delivery. The evolutionary impact of this decision can no longer be ignored.

C-section has allowed heavier babies to survive; it has bypassed evolutionary punishment. But there’s more. Not only does it allow for preservation of large heads, it also permits the passing of genes that govern pelvic size. A mother with a small pelvis who has just given birth to a baby with a large brain has also passed along her genes responsible for the small pelvis. Logical evolutionary progression would suggest that the brain would get larger and larger and the pelvis would either remain the same or become smaller (many other factors govern pelvic size and the smaller it is, the easier it is for human mobility) and so there will come a time when natural birth would become impossible and C-section the only viable option.

But while C-section babies might alter the course of human evolution – retain smaller pelvises, possess large brains – nature has its own way to getting back. It turns out that a baby’s primary defence against infections, asthma and allergies are the microbes it receives while being squeezed through the vagina and into the world. Vaginal fluid contains an astounding diversity of microbial flora that C-section babies miss out on. Indeed, scientists are now of the opinion that vaginal fluid is as crucial as mother’s milk, so much so that doctors in the West have begun bathing the new-born with it. Clearly, the vagina speaks in many voices and not just a monologue. Its bacteria and immune derivatives are a priceless gift to the bundle of life that has just struggled past unconcerned.  

In the coming million-odd years, neuroscientists believe the human brain would grow to a size more than double of what it is today. The pelvis, on the other hand, would not change much unless we reject bipedalism for quadrupedalism. The onus of propagating the human race, therefore, would rest squarely on surrogate mothers with exceptionally wide pelvises or, more likely, the C-section. Unless, that is, engineers and biologists get together and create the perfect artificial womb. Who knows, they might yet evolve to do exactly that.

Note: An abridged version of this article was published in DNA.

The author can be contacted at and on Twitter @ARangarajan1972

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