Benefits of having pets and why people own pets

So what are the benefits of owning pets in general? Why do people own pets? What are the benefits of owning each individual species? Such as having a dog, or having a cat, or having an aquarium, etc.

Can any of you make a good list with detailed benefits?
It doesn't matter even if you can just provide information on a single species.
You can state your opinion, as well as the proven research from studies. In the case of posting information from studies, please provide links to the sources.

My opinion is people just like having certain pets, for many varied reasons. We generally have a preference as to what pet we like for what ever reason. I like dogs best. They are loyal (usually), playful, affectionate and can do some pretty funny stuff. Dogs are company. Sometimes older people that live alone like having a dog or cat to keep from being alone. It gives them some place to put their love and affection. Keeps them from being as lonely. Families with kids, well, the kids like playing with the pet. I think most people like to be needed, a pet needs us. Back to dogs, they are really something. They are always glad to see you. You come home from a rough day, there is that tail wagger so very happy to see you. Your dog will not judge you if you have warts, are overweight, have three arms, the dog just does not care. Dogs are incredibly forgiving too. Unlike people who tend to be a tad two faced at times, you know where you stand with a dog. I remember something I read somewhere once, "Lock your wife and your dog in the trunk of your car. After two hours open the trunk. WHO is glad to see you?" Evidently that one is all over the internet.
Then there are the health benefits to having a pet. The following is a copy from a website:
Most households in the United States have at least one pet. Why do people have pets? There are many reasons. Some of the health benefits of pets are listed below.
Pets can decrease your:
Blood pressure
Cholesterol levels
Triglyceride levels
Feelings of loneliness
Pets can increase your:
Opportunities for exercise and outdoor activities
Opportunities for socialization

Many groups support the health benefits of pet ownership. You can learn more about the health benefits of pets and how to keep your pets healthy by visiting the following sites.
http://www.cdc.gov/healthypets/health_benefits.htm

I can only speak from my own experience on this subject. I would say that I have taught my preschooler to be gentle with animals, and to respect them. I also have taught him how to take care of the dogs, because he helps me wash them and fills their water dishes. He is an only child and he loves that he has his friends to play with at home. I like having the dogs at home, because they inform me when people are around our house. They are cheaper than a home security system. I never feel lonely when I have the pets. They give me unconditional love.

In my opinion, pets can really help if you are feeling lonely. They are always there for you. But that's just one of the benefits of having a pet and just one of the reasons people get pets. They are just a pure joy to have. They are always happy to see you, they love you, they are so very loyal, they love to play with you.

For me, dogs are just incredible to have around the house. To me, they make a house a home. They sit with you, they listen to all the things you say. There have been countless times where I have sat down with my dog and told him all my troubles. No matter what was going on in the world, I could always count on a hug from my dog, my best friend, and he always smiled at me.

Another benefit to having a dog, specifically is the exercise. Just walking a dog 3 times a day everyday really helped me lose a lot of weight. I became very healthy and I love the outdoors all the more when I'm with my doggies.

I have anxiety related problems and high blood pressure because of it. My pets, both cat and dog, are able to help me cope with panic attacks and sometimes it seems like they are the only ones who truly understand how I feel. Its strange, on my worst days I'll break down and start crying but my cat picks up on this and hops right into my lap, starts making biscuits and I'm laughing.

I do not have any fur pets here anymore due to one of my children being highly allergic to cats and dogs. We used to have a dog and her name was Lady. Lady was our watch dog. She basically took care of watching our house. She would chase away strangers and even strange animals. Lady was a loved family pet. Even with her being a mostly outside dog, my son was still having attacks. We had to give her away to a great home. This dog was so very gently to anyone she encountered except the ones she felt dangered by.

Animals can be great for a variety of reasons. I personally had one as a pet. Some people train and show them. Others like the company. Whatever reason they choose to have a pet, it's a good reason.

I think that there are a variety of reason why people keep pets, going back hundred of years to the time when the half-wild dogs stayed around the human camps to glean the food scraps; and then became the camp guard dogs. I like to imagine that families adopted some of the little puppies, and raised them as pets for their children. After that, the bond was started, and humans and dogs have lived together ever since.
Dogs learned to guard the flocks, and even to herd the sheep, and alerted the shepards to attacks by hungry wolves.
As life became more settled, dogs and cats made the transition to becoming our house pets, and through selective breeding; we have developed just about every size and shape of dog that is possible. People that want large dogs can have one, and little old ladies like me can have our toy-sized Yorkie-poo to keep us company around the house.
Personally, my Chipper is like my little friend that is always there, and I can talk to him about everything. He always seems to listen intently, and never fails to keep a secret. So, to me the reason we have our pets is because they love us so much, and accept us no matter what.