The following article explores the idea that the reason having a dog lowers high blood pressure, reduces anxiety and stress, and improves a person's general health is that humans and dogs have evolved together. If you're looking for a stress management technique, if you're looking to reduce blood pressure of find stress relief, you would be hard-pressed to find a more enjoyable solution than getting a dog.

EARLY ONE MORNING, Pearl Carlson of Granite Falls, Washington, woke up because her dog was trying to pull her off the bed. The house was on fire.

The dog saved the lives of Pearl and her parents that morning. The most amazing thing was what they discovered afterwards: The dog had splinters in his mouth because when the fire started, the dog was outside. He chewed his way through a plywood door to get into the burning house to save his family. He got burned pretty badly. The chain around his neck got so hot it burned his throat, making it impossible for him to bark.

We've heard true stories like this before — dogs saving people and people saving dogs. The two species have a great fondness for each other. This fondness has deep roots.

Dogs and people evolved together. We formed a symbiotic relationship long ago and became a kind of superpredator.

A symbiotic relationship means two species are better off together than they are apart, that they contribute to each others' ability to survive. Lichen is a good example. Lichen (that yellow and orange stuff that grows on rocks) isn't one species, but two. It is a symbiotic relationship between a fungus and an alga. The fungus provides a protective scaffolding on which the alga can grow, and the alga provides a specific carbohydrate the fungus lives on.

Two species living together in such close association tend to effect each other. The presence of one will effect the evolutionary adaptations of the other.

A group of humans in a partnership with dogs would survive better than a group of humans without dogs in our prehistoric past.

When our relationship began, the our ancestors and our dogs' ancestors (wolves) ate similar foods and both species hunted in groups. Both species are extremely social and survive by cooperating with each other. But each species has different strengths. Wolves are good at chasing large animals but not as good at killing them. Sometimes they'll corner a large animal, like a moose, and try for several days before they manage to kill it. The human-dog superpredator was able to kill animals that either species by itself would find difficult or impossible to kill. Both dogs and humans ate more if the dogs could corner prey and humans could kill it.

"With its speed and tracking ability," wrote Michael W. Fox, "the dog was an ally in the hunt, and it kept us warm at night with its higher body temperature and was protector and playmate for our children."

The two species fill each others' gaps. Dogs don't see as well as humans. People see more color and detail. A tremendous amount of the human brain is devoted to vision. But dogs have much better peripheral vision and they are considerably more capable of perceiving movement than people are.

Dogs can hear much higher frequencies that humans. A dog's brain has twenty times more olfactory neurons than a human brain. Donald McCaig wrote, "Since dogs could hear and smell better than men, we could concentrate on sight."

And even our tastes complemented each other well. Animal behaviorist Dennis Fetko points out that humans usually ate the meat and fat, "while throwing away the very things wolves craved — bones, offal, fur, horns and hoofs."

"By tapping wolves' protective, territorial instincts," wrote Lowell Ponte, "our ancestors acquired watchdogs. Other predators such as bears tended to avoid them."

While we were selectively breeding wolves to produce characteristics we wanted, their skills and companionship may have allowed us to evolve in certain ways. We didn't need to rely so much on our sense of smell, for example.

The combination of dog and human creates a superspecies with greatly expanded powers. This superspecies can hear very high frequencies, see great detail in color, detect movement extremely well, and has great peripheral vision. This superpredator can detect the faintest odor in the air of enemy or foodsource and has the endurance and speed to chase down any prey and the ability to make weapons that will kill any prey.

We have benefited greatly from our alliance with dogs. And they also gained benefits. Dogs have nearly twice the life-span of wolves in the wild.

There might have been a kind of selection for humans who liked dogs. It is entirely possible that we have evolved to enjoy the company of dogs. That may be why dogs have a good effect on our health and moods. It may be why merely petting a dog lowers a person's blood-pressure and general anxiety level. Whatever the explanation, most people respond to dogs, particularly their own dog, with a general lowering of anxiety.

Researchers at Cambridge University found that after getting a dog, a person's general health improves. "Dogs help us psychologically," writes Toyoharu Kojima, author of Legacy of the Dog. "Tests have shown that walking a dog, or just having one as a companion, effectively helps speed recovery from an illness and aid in rehabilitative efforts."

UCLA researcher Judith Siegel studied a thousand elderly people. Those who owned a dog required twenty percent less medical care than people without a pet.

So here is an anxiety-lowering and stress-reducing method that may not have occurred to you: Get a dog.