Put a boy in pink and give him a Barbie and he would most likely end up playing with dolls' houses and applying mascara. Dress a girl in blue and give her an Action Man figure and she would end up demanding Panini football stickers for her birthday.
We all knew it was rubbish. And my own experience with my two children demonstrates it. Despite being treated in exactly the same, gender-neutral way, Lucy likes things that are furry, fluffy and preferably pink, while three-year-old Alex prefers fire engines and all-in wrestling.
Now a new map of the human brain produced by scientists proves that we are not just distinct sexes, we are practically different species.
The study found that women devote more brain inches to decision-making and emotions, whereas we guys are hard-wired to spend nearly all our time thinking about sex - even more when we are actually in sight of a woman.
The fact that my brain is very different from that of a woman comes as no surprise to me, despite the fact that I am in touch with my feminine side. I am an expert at interpreting emotional shifts from the most subtle of signals. For example, if a woman is throwing shoes at you or screaming very loudly, it means you didn't ask her something important about her life - probably to do with shopping.
Not every man has my mastery of the female brain, however, and this means our interactions with women are bound to be fraught. Similarly, women tend to misinterpret male behaviour. Therefore, for the benefit of those readers, I am happy to reveal the different ways men and women tend to think about the same subjects. Obviously, this is completely and utterly scientific.
Her: I'm really looking forward to seeing my friends in Hampstead. It will be lovely to catch up with them and see how they are coping with the baby.
Him: Hmm, Hampstead, I wonder how bad the traffic will be on the Finchley Road. We'll probably need petrol on the way home.
Her: I could do with some new tops. I'm going to spend the whole of Sunday going to Brent Cross to hunt for bargains in the sale. It will be such fun.
Him: Nearly all of my shirts either have holes or stains. Sometime next year I'm going to have to think about nipping out to the shops in my lunch hour and buying a few. I wonder if I'll be able to get away with not trying anything on.
Her: These kneidls are delicious I wonder how many calories are in each one?
Him: These kneidls are delicious. I wonder how many I can get in my bowl?
Him: The new carpet is great. That's the redecorating sorted.
Her: The new carpet is great but it just doesn't go with the curtains. We'll have to get new ones.
Her: I'm so upset. I've had a terrible day at work and all he can do is sit there watching football like a zombie.
Him: Goodness, she's crying. If I say something really sensitive and soothing and make her a cup of tea, maybe she'll be OK by the time the second half starts.