I don't know where I heard it, but I did somewhere, lol. Sorry, i can't show you!
I think the main thing that makes having pets help you live longer is the love and attention they give you!
The majority of dogs seem to be more affectionate than the majority of cats. I'm not saying this about ALL cats and dogs, just generalizing them as a group (I know there are some mean, loner dogs and some very very loving cats) .
Dogs tend to be more loving and always want to be with you. They're more dependent on people for love. Even in the wild, wild dogs (such as wolves) are always in groups. They depend on eachother. I know my dog fits this... she ALWAYS wants to be with us. When I'm in my room she'll come and jump on my lap. In the morning she'll bark until we go see her. The love I get from her helps me a lot...
Cats can love their family, they're just more independent. Cats in the wild are like that to. All the cats I've known are like this... They'll give you love, but they want their space sometimes too!
I think all animals are as affectionate as the owner teaches them to be. I think that's true from cats, to dogs to birds, to reptiles. I don't think any animal is more affectionate than any other if raised properly.
I do agree that Dogs need more attention than cats though, which is both a good thing and a bad thing. Cats can entertain themselves where as a Dog needs companionship most of the day. And yeah, this is cause of their nature... in the wild cats usually travel alone where as Dogs are pack animals.
A friend of mine has the most adorable golden retriever puppy, Harley. I love goldens, but they grow up to be so big that I don't think I could ever deal with one...... I just travel too much to have a dog right now