Q. Why do dogs delight in chasing and returning a ball or stick?

A. Conclusive research is lacking, but several plausible theories have been offered to explain why so many dogs love to play fetch.

Many dog-behavior experts link the behavior to primeval prey-carrying, in which the ancestors of today’s dogs took their kill back to the den to share or hoard.

The instinct is especially well-developed in certain breeds — including retrievers and spaniels — that have been selectively bred over the centuries to propagate dogs that are especially good at retrieving objects for their handlers.

Some dogs can become obsessed with chasing a ball and want to do it constantly. Some Norwegian researchers have suggested that this can be a true chemical addiction to the hormones like adrenaline that are released by the excitement of a game that mimics hunting.