Hal Herzog, professor of psychology at Western Carolina University, had long wondered why people choose the types of dogs they select for pets. Working with colleagues at University College London and the University of California-Davis, Herzog examined American Kennel Club records of more than 40 million purebred puppies registered in the United States over the past 50 years.

His findings? Man picks man’s best friend not on the basis of reason or because the breed inherently makes a good pet. Instead, it’s a matter of what’s trendy, Herzog says. The results of the study were published in the April issue of the Royal Society’s Biology Letters, a scientific journal in Great Britain, and have attracted quite a bit of attention in the British press.

Dogs were originally selected for domestication for such utilitarian reasons as hunting or herding, but since then, service has been replaced by fashion, he said.

“A person selecting a pet dog seems to be highly influenced by choices being made by others at about the same time, without his or her knowing it. In this respect, dog breed popularity is no different than changing tastes in food — remember fondue pots — clothing styles or music. They have become fads.”

Swings in popularity of certain breeds can be dramatic, and sometimes can be traced to a specific event, such as the popularity of Dalmatians after recent Disney movies, Herzog said.

“More often, however, there is no apparent single cause of swings in popularity, such as the booms that occurred in Doberman pinschers, chow chows and Saint Bernards. The popularity of some breeds can just take off, much like a social epidemic.”

In their study, Herzog and his colleagues say they have demonstrated that most shifts in the popularity of dog breeds in the United States can be attributed to a process called “random drift,” in which individuals simply copy the choices made by others. The result, they say, is that many breeds become popular just by chance.

So, what are the current trends in dog breed popularity? In 2003, the most popular breed in the United States was the Labrador retriever, followed by the golden retriever, German shepherd and beagle. Breeds on the rise include the Havanese, cavalier King Charles spaniel, Brussels griffon and French bulldog, while the Dalmatian, chow chow, rottweiler, akita and Pekinese are on the decline.