Dogs were the first domesticated animals. There remains debate about the origin of the first domesticated dog, these disputes centering on whether the first pet dogs emerged in Europe, the Middle East, or East Asia. The earliest known evidence of a domesticated dog is a jawbone found in a cave in Iraq, dating to about 12,000 years ago.
Archaeologists and historians agree that the first dogs were essentially tame wolves, attracted to the garbage that early civilizations would throw out. As it became easier for these dogs to get food, they lost their aggression, no longer needing to hunt in order to be fed. In turn, they gradually became the ideal companions. Human beings began to breed dogs to help with hunting, herding, and guarding.
As the structure of society changed and civilizations began to grow crops, cats began to self-domesticate. They would move to crop fields to catch the rodents common on farms. Cats are the only animal to live solitary in the wild, as opposed to living in packs, herds, or flocks. Perhaps this is why the cat never lost, in the human mind, the quality of mystery. Cats had particular pride of place in Ancient Egypt, where they were deemed sacred (Cleopatra is believed to have had a cat of her own). An Egyptian farmer was perusing his farmland in 1888 when he noticed a rather large tomb. It was filled with 80,000 cat mummies.
The difference in the paths to domestication of dogs and cats could explain the difference in their behavior. Dogs tend to be dependent on their owner, whereas cats are often described as more independent, with a mind of their own. The cat has been able to take what it wants from man (food, shelter, play) and to pay its dues in return (pest control), without losing contact with its original identity. Cats have remained closer than other domesticated animals to their wild cousins, partly because it is so difficult to control their breeding. They are more able than any other to fend for themselves if human support is withdrawn.
The debate between "dog people" and "cat people" continues, often to ridiculous lengths. In 2009, a study purported to have determined that the annual carbon footprint of a dog approximated that of a Humvee; the annual carbon footprint of a cat was equivalent to that of a Volkswagen Golf.