If we're so unhappy and fed up with monogamy why don't we ever want to talk about ditching it?

Hey, dude walking three metres in front of your girlfriend - you do know she's not a dog or a small child?

Maybe you've had an argument … but … no, now you've turned to show her a $247 T-shirt in a shop window and she's nodding distractedly before you charge off again.

Coupledom has its challenges - the most widely nominated being sex, monogamy, children, money and ''their'' parents - so it seems just walking beside your partner should be a cinch.

Wherever I go, however, I see this scenario - men and women strutting ahead of their beloved, a perfect projection of how out-of-step a partnership can become.

Maybe it's just momentary bad vibes, or perhaps it's a deeper contempt, dismissiveness, or frustration that ''this is all there is''.

After all, most couples meet at the ''right'' age, have much sex, decide this is probably as good as they can get, move in together, marry, breed, get fat and become asexual because the only person they're allowed to fornicate with doesn't want to.

How long's this been going on? Much has changed in our modern world, from the way we eat to how we consume information, earn money and spend our leisure time. Yet ancient institutions like monogamy remain the same.

Many argue the human brain is not handling the pace of change in technology - that we suffer increased rates of depression, anxiety and loneliness, so the constancy of traditions such as marriage are a rock we can all still build our lives upon.

What if, however, it wasn't the human brain struggling to cope with change, but our outmoded institutions - such as marriage, monogamy and an education system older than this (white) country?

Consider this: Before 1880, the majority of people had never seen moving pictures. If they'd witnessed a lion charging at them, it was because a lion was actually coming to eat them.

Then, along came film and people could experience a lion scaring them without the accompanying danger. That's a wild shift in perception, yet our brains handled it - just as they've dealt with travel at previously inconceivable speeds, flying, murdering each other in 3D and surround sound, and maintaining social networks.

Marriage, however, is an institution thousands of years old, designed largely to protect hereditary property (via monogamy), ensure ''someone for everyone'' in small, sparsely populated rural communities, and to produce children to work the farm.

Today, fewer than one in a hundred Australians live on farms, the majority of us bumping around cities that provide every stimulus and opportunity for anonymous sex with multiple partners.

British historian James Burke speculates humanity has now entered a period of transition.

''We live with institutions set up in the past to solve the problems of the past, with the technologies and values of the past, and we wonder why they don't work too well any more?'' he says.

So we blame promiscuity and divorce on ''bad'' morals, rather than a once good idea gone bad … or at least near obsolete.

This article If we're so unhappy and fed up with monogamy why don't we ever want to talk about ditching it? was originally published in The Sydney Morning Herald.