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"Some things that happen when you're a teenager do just seem to be bad design, just a bad side effect of evolution. But most are all going somewhere positive, somewhere quite healthy," says veterinary anatomist David Bainbridge.

He stays up all night playing video games, drinks beer behind the school with his buddies and growls when you try to haul him to grandma's for dinner.

But we should be giving him a break, according to University of Cambridge veterinary anatomist David Bainbridge.

After all, your teen is enduring the toughest, most crucial stage of our species' development, a transitional journey many parents struggle to understand, Dr. Bainbridge writes in his new book, Teenagers: A Natural History . Adolescence is the most important part of our human lives, he professes in the book, which explains teenage changes through the lens of evolutionary science.

The Globe and Mail talked to him about why we ought to ditch the stereotypes and embrace teenagers for the hormone-driven, hyper-emotional, sometimes-reckless creatures they are.

This book is meant to explain why teenagers exist. Isn't there a simple answer - that it's just a natural bridge from childhood to adulthood?

Other animals that take a very long time to grow up, like whales and chimpanzees, they're all pretty much finished when they're about ten, whereas humans, though we live a similar length of time, it takes twice as long. The more I looked into this, the more I realized the second decade is really something that is unique to humans. Many of the things that really make us unique, like planning all of our highest cognitive functions, we develop when we're teenagers.

Why do you say the teen years are a human's most pivotal?

Everything is established around this time - you establish your relationships, your social life. Especially important is you establish the way you think about yourself, you establish your romantic and sexual relationships. And unlike when you're children, you kind of have to do it on your own.

How does evolutionary science help us understand teenagers?

It gives you reasons for why things happen. I think when you're a teenager and tough things are happening to you, one thing that helps is to know there are other people who are going through the same things as you. Some things that happen when you're a teenager do just seem to be bad design, just a bad side effect of evolution. But most are all going somewhere positive, somewhere quite healthy.

Like what?

Like how we deal with our emotions. Adults have deep sensors inside the brain that generate their emotions, then they have other centres more toward the surface to moderate and control those emotions. Now when you're a teenager, we believe the bits of the brain that generate the emotions mature first before the bits that control them. That's why many teenagers get very, very violent emotional reactions to things that they don't seem to reign in quite in time.

Which stereotypes do you explain with more clarity using evolutionary science?

I think one of the most noticeable is their ability to take risks. You have to learn to deal with risk-taking, you have to learn to play with your social interactions and interact with different people in different ways. And nowadays, that's mainly interpreted as unnecessary risk-taking and rudeness. We still have the brains we had 20,000 years ago and we're probably very good at assessing the risks and the social world we had then. But the risks have changed around us. They're not falling out of a tree or getting eaten by a lion. They're driving on wet roads or having unprotected sex.

Then there's sex. It's completely natural for teens to do it, you write, though parents may raise their eyebrows.

Many people are sexually happy and well adjusted by the time they get to 21. And usually, that's because they've had sex with people. There's a bit of a contradiction in adult attitudes to sex, that we want people to get to that stage by their early 20s, and yet we don't actually want them to have any sex.

And how about drugs?

My attitude towards this changed as I was researching it. I was very liberal going into this and I know what it's like as a teenager to drink alcohol or take drugs - it's fun.

What changed your mind?

All the change that's going on in the human brain and how in a way the brain is quite malleable when you're a teenager. Teenagers respond to drugs differently than adults, for example, they're sedated much less by alcohol. The sedation is usually what stops you drinking. It just looks a bit too risky for me. I think waiting until you're about 18 or 20 is probably safer.

Do you think teens can use a lot of this stuff as a get out of jail free card, like 'Mom, I'm having sex because I'm meant to.'

I think they can. Many people look back on their teenage years and they think about the various things they did - sex and maybe some of the risky things they did, and they were nostalgic about them and they don't feel bad about them. And I think we just have to accept that if the teenagers say that to us, then maybe they're right. Maybe in 20 years time you'll be able to tell.

That's pretty demanding for a lot of parents.

The bottom line is we've evolved teenagers to make us successful adults, we didn't evolve teenagers to make life comfortable for parents.

So we should be cutting teens a little slack?

I think so, yeah. Though it won't make it any easier to deal with them.

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