People love dogs. We feed them lobster, take them to spas, sleep with them in our beds, buy them sweaters and booties, and delight in all but their pooping. To those with no canine, this adoration appears absurd, expensive, and gross. The investment, though, may be worth it. Dog ownership, new research shows, is a form of natural insurance offering health and longevity, along with the affection of an animal companion.