But, how does having one affect us?

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My name is Meg Olmert and I'm the author of "Made For Each Other: The Biology of the Human-Animal Bond."

Our journey with dogs began about 45,000 years ago, according to the latest archeological evidence.

It preceded many hundreds of thousands of years with a more casual, and perhaps distant, pragmatic relationship with wolves as well.

But about 45,000 years ago we start to see the bones change and indications that A, dogs are certainly living with us and that living with us appears to have had certain effects on their biology and their physiology.

That is what enabled them to become our best friends.

How does this relationship work?

There is a feedback system that both neurochemically, and psychologically, and behaviorally that sets up between you and your pet.

And how good you are to your pet is often exactly reflected back.

Although, what I would say is they tend to be wildly generous.

More generous than we are.

So, that is why, you know, they'll be wagging their tail, you know, thrilled to see you when you come home or if it's a cat, it's purring, and you may be very distracted but they aren't.

You are the greatest thing they ever saw if you've developed this relationship.

If you've earned it.

You have a different relationship with your own pet versus your, even your neighbor's pet, because it's, that's your closer family.

It's a different kind of bond and when they do FMRI studies, just like a mother will have certain brain regions light up very strongly in the dopamine and oxytocin-rich areas when they look at a picture of their baby versus just another infant.

When you look at a picture of your dog versus another dog, you see the same thing.

If you love dogs you're gonna get this reward

to a degree whether you are looking at your dog or not.

Do therapy dogs work?

Well, they certainly can.

Dogs can do amazing things.

With our program, Warrior Canine Connection, we work with service members and veterans with post-traumatic stress disorder.

We have the patients who say, "This dog is better than any drug I ever took.

I didn't sleep for five years until this dog slept next to me."

What happens to your body when you're with your dog?

Your heart rate comes down, your blood pressure comes down, your heart rate variability, which is the ability of the heart to duck and dive and respond to stress improves.

You release oxytocin, the opioids, adrenaline, and serotonin.

So, all of these great reward chemicals and anti-stress chemicals can be released in both you and the pet.

What is oxytocin?

Oxytocin is a very ancient chemical.

It's in all social mammals.

There's variations on it that you find in birds and in turtles, and in worms.

And it most effectively is known for releasing breast milk and creating labor contractions.

That's what it was first known for.

So in a sense, it is the quintessential mammalian hormone since live birth and production of breast milk identifies us as mammals and mammary glands, etc.

About 25 years ago, they discovered that besides the oxytocin receptors and cells in the body that are producing oxytocin in the breast and the uterus, long behold, it's produced throughout the brain and in all the areas that control behavior and emotion.

So what was it doing there?

And what they discovered was that it was talking to other classic brain neurotransmitters, such as serotonin, and dopamine, and adrenaline, and the opioid system.

And it was setting up, by doing that, this perfect mental physiologic state of calm.

It is the most powerful drive and it creates the bond that lasts a lifetime.

That's how strong it is.

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