When you remember that men are from Mars and women are from Venus, everything can be explained," wrote John Gray, in the introduction to his infamous book.
Every so often, we get one of those 'Men Are From Mars, Women Are From Venus' moments, when the sexes are split right down the middle on an issue.
This split is seen again in a new study by computing guru Stephen Wolfram.
Using the personal analytics of more than a million Facebook users, recording the statuses, likes and interests they posted on their profiles, Wolfram has created a detailed picture of Joe and Jane Bloggs and their hobbies. The result? The genders are almost totally divided when it comes to hobbies and interests.
We all have anecdotal impressions about typical hobbies for men and women.
Men are more likely to spend hours happily absorbed in car or motorbike maintenance, light aircraft piloting, reading sci-fi, tweaking their sound systems, playing computer games, or programming.
Women are more likely to spend their time happily immersed in coffee mornings, or dinner parties, counselling friends on relationship problems, or caring for friends, neighbours, or pets.
This latest study shows how men and women develop new interests as they mature – and how the genders are very divided.
Men typically talk more about sports and technology than women – and, surprisingly, they also talk more about movies, television and music.
And men start to shift their focus away from the workplace after age 30, while women don't do so until eight years later.
If middle-aged, a failsafe topic for any audience is the weather – a key interest for most people as they settle into middle age.
Now we know why marriages don't last anymore: couples are too close in age. It's not that the sexes don't share interests, but that they peak at different times.
Women might be into books at 22, but men not until they're 50.
Fashion sense for both starts early, at just 16, and politics later on at around 60, but more often female interest in something crests well ahead of men.
Says Wolfram: "Some of this is almost depressingly stereotypical. And most of it isn't terribly surprising to anyone who's known a reasonable diversity of people of different ages."
So what's causing this?
Well, there has always been a divide in the toys we give children to play with. It's a dichotomy of the sparkly tiara versus the microscope.
Increasingly, though, parents and their children have been demanding a change in the way toys are marketed.
Just last week, Merida, a new doll in the Disney Princess line-up, caused buckets of controversy. Merida's strong, positive portrayal of young womanhood in recent movie, Brave, had made her a unique Disney princess.
But she was given an extreme makeover that hyper-sexualised her teen looks.
A petition at change.org already has more than 120,000 signatures.
The potency of early learning means that what children learn early on, often through their toys, has a huge impact on what they become capable of later in life.
By imposing these categories on children through the options we give them, we put limits on what they might become.
Why would we want to limit the scope of possibility?