There are few relationships in the animal kingdom as close as that between humans and dogs. The latter have become the ultimate parasite — using big, soft brown eyes to woo humans. In return for the endorphins released when the dog deigns to allow its human to pet it, the hairy mammal gets fed and kept warm at night.
That relationship started out on a more equal footing some 30 000 years ago, when grey wolves started hanging around human settlements to scavenge for food. Preferring takeaways to chasing down a meal, the wolves gradually stopped attacking humans. Those humans, in turn, realised that wolves would be good protection for a species devoid of natural weapons.
Over time, this relationship grew to the point where humans and dogs started evolving together. What was good for one was good for the other. This is why dogs can break down starches whereas their more meat-attuned wild relatives refuse to eat food from a plant. For them, real food needs a whiff of fresh blood about it.
Researchers from Emory University in the United States sought to work out how much dogs had evolved to depend on humans. This meant lots of playing with Labradors, golden retrievers and all sorts of other fluffy dogs — all in the name of science.
In the main experiment, dogs were trained to associate three different objects with three different outcomes. Picking a pink toy meant a food reward and a blue toy led to verbal praise. Any dog that chose the third object — a hairbrush — got nothing, as a way of creating a control. Most of the dogs picked both rewards, but a quarter of the pets kept picking the blue toy and affection over food. Two dogs kept picking the brush — proof that not all dogs are clever.
Lead author Gregory Berns said in the research: “One theory about dogs is that they are primarily Pavlovian machines: they want food and their owners are simply the means to get it.”
The Emory research helped proved otherwise, he said. “Another more current view of their behaviour is that dogs value human contact in and of itself.”
The team’s findings were published in the journal Social, Cognitive and Affective Neuroscience.
So your dog might not only be a well-evolved parasite. It could also just love you.