The poor old placenta. It really doesn’t get much public attention. And yet it does a crucially important job – acting as the interface between the mother’s blood supply and that of her developing foetus.
Every molecule of glucose, oxygen and many other essential compounds consumed by the voracious offspring passes across the placenta – from the mother’s blood to the foetus’. And waste products pass back the other way to be detoxified and excreted by the mother’s organs.
Given these roles, one might be tempted to see the mammalian placenta as a discreet anatomic servant, working tirelessly, unseen and largely without thanks for the mutual good of mother and foetus. Only to be discarded or eaten after birth and spared no further thought.
And occasionally be venerated in YouTube videos with mystical soundtracks:
But such a view underrates one of the most interesting organs that ever evolved.
Your ancient Greek-Latin binomial for the day is hyperemesis gravidarium. HG for short. It’s a particularly extreme form or pregnancy sickness (or morning sickness). Brought to you today by Catherine, The Duchess of Cambridge, who was hospitalised yesterday with the condition.Pregnancy sickness, and HG in particular, illustrates the complete absence of intelligent design in nature. It’s the kind of condition that even a vengeful and misogynistic deity would have trouble conceiving. HG, as you have probably read a dozen timestodayalready causes severe vomiting and an inability to eat or take in fluids. As a result, dehydration, weight loss and their metabolic consequences can become life-threatening.
Before the advent of intravenous rehydration, an appreciable number of women with HG died. The most famous casualty until now: author Charlotte Brontë who died in 1855, four months pregnant after severe HG left her unable to take on food or water.
I am sure the former Kate Middleton is in capable hands at London’s King Edward VII Hospital, and I do hope she and the several million other women suffering from HG right now make as rapid a recovery as possible. As we are due to endure incessant Royal baby chatter and HG sympathy over the coming months, I thought I’d sneak in quickly with an important lesson that HG and pregnancy sickness illustrates about evolution.
What use is pregnancy sickness?
One might expect something as awful but common as morning sickness to have a damned good adaptive explanation. In fact, while many explanations have been put forward, the obvious ethical difficulty in doing experimental tests makes it hard to separate the good ideas from the bad.
Morning sickness has long been explained as a way for mothers to avoid food poisoning that can devastate a growing foetus. If a woman is too nauseous to eat, and if the most dangerous foods revolt her, then she limits her chances of picking up dangerous bacteria like Listeria which cause food poisoning.
But pregnancy sickness might also be a manifestation of a simmering gestational battle between mother and foetus. Pregnancy takes a huge toll on a mother and uses up a large chunk of a mother’s reproductive lifespan. Given these costs, if a mother’s body detects signs that a foetus has little chance of thriving, her body will often spontaneously miscarry that foetus.