John Archer, a psychologist at the University of Central Lancashire [Preston, UK], has been trying to figure out for some time why people love their pets. In evolutionary terms, love for dogs and other pets “poses a problem,” he writes. Being attached to animals is not, strictly speaking, necessary for human health and welfare. According to Archer, while it is true that studies show that people with pets live a bit longer and have better blood pressure than benighted non-owners, yet in the literal sense, we don’t really need all those dogs and cats to survive. Archer’s alternative Darwinian theory: Pets manipulate the same instincts and responses that have evolved to facilitate human relationships, “primarily (but not exclusively) those between parent and child.” Or, to look at it from the opposite direction, Archer suggests, “consider the possibility that pets are, in evolutionary terms, manipulating human responses, that they are the equivalent of social parasites.” Social parasites inject themselves into the social systems of other species and thrive there. Dogs are masters at that. They show a range of emotions—love, anxiety, curiosity—and thus trick us into thinking they possess the full range of human feelings.