The Babies That Learn Before Being Born

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From cuttlefish learning to recognise prey before they hatch, to birds memorising "passwords" in the egg to form a bond with their parents, it is clear that schooling begins before birth

While pregnant with my first child, I heard unsolicited advice typical of that showered upon expectant mothers.
"Don't eat spicy food," and, "Avoid garlic, especially when you're breast-feeding." But as a spicy food-lover I was sceptical, and reluctant to take heed. Human cuisines vary all over the world. Surely babies born to mothers in some of the world's spice capitals must learn to get used to breast milk with more flavoursome notes?

It was pure speculation on my part, but my personal experiment – played out with an unscientific sample size of just one – offered some support. My tiny experimental subject expressed his prenatally-learned love for Thai curry and garlic-spiced breast milk by way of contented guzzling, then guzzling some more.

Some more rigorous scientific research also supports the idea that babies learn taste preferences before they are born. In fact, prenatal learning is not limited to taste. Nor is it limited to humans. What is emerging from the experiments is evidence that all sorts of animal species great and small learn about the world before entering it by paying attention to the tastes, smells, sounds – and even sights – available pre-birth.

So can a zest for garlic be learned prenatally? Peter Hepper of the University of Belfast decided to find out. He and colleagues tested children born of mothers that often versus never consumed garlic during late pregnancy.

His study involved just 33 children, but his results hint that a learned prenatal preference for garlic was maintained even years later, as seen in a willingness of kids born to garlic-consuming mothers to eat garlic-flavoured potatoes when they were aged eight or nine.

How do human babies taste food in the uterus? There are several possible routes to flavoured womb service.
One idea, explains Hepper, is that flavours pass into the amniotic fluid, so when the foetus starts to swallow – which it does from about the tenth week of development – "it will experience the flavours as they come through".

Flavours might also bypass the mouth and pass directly into the foetus's blood through its mother's blood. This might be particularly true of garlic, which can linger in our systems for hours after a meal – explaining why people close by can smell the stuff on us even the next day.

It is not just strong flavours like garlic that can influence foetal tastes. The same may be true for subtle flavours too.

In an experiment at Pennsylvania's Monell Chemical Senses Center (and sponsored by a baby food company), researchers gauged babies' reaction to plain versus carrot-flavoured cereal. Some of the babies' mothers had spent the last trimester of pregnancy and first months of breast-feeding drinking carrot juice and water, while other mothers had stuck to water alone.

Based on the extent to which the five- to six-month-old babies grimaced at their plain versus carrot-flavoured cereal, the researchers concluded that a keenness for carrots can be learned prenatally from their carrot-infused amniotic fluid, or postnatally from the carrot-flavoured milk they drink.

This might all seem a bit trivial, but it is really not. In mammals in general, taste and smell seem to be important triggers that babies look for before initiating suckling.

"When the baby is put to the breast, it experiences the same flavour that it's been sucking for the last 30-odd weeks before birth, so it's quite accepting of milk," says Hepper. "If it's a different flavour, it's perhaps more problematic."

Unsurprisingly, then, prenatal flavour learning is widespread across mammals. It is seen in rabbits, rats, dogs and cats, for instance.

It may have evolved because it is important in steering us towards safe foods, and in offspring recognition of their mother. "It makes sense," says Hepper, "to be programmed to respond to our primary caregiver, the one who is programmed to care for us."