­The relationship between people and dogs goes back at least 15,000 years, making dogs potentially the first animal to be domesticated. In that time, dogs have played many roles and performed many jobs for their human companions. Dogs come in a startling variety of shapes and sizes, but from the giant and noble Great Dane to the tiny and tenacious Chihuahua, they are all one species with one basic history.

In this article, we'll explore where dogs came from and why they look and act the way they do. We'll also learn what recent genetic work has to tell us about our dogs and talk about how to find the right dog for you.

The Dawn of the Dog

Dogs are members of the family Canidae. Canids are part of a larger group called Carnivora, which also includes bears, cats and seals. Fossils show us that Canidae split off from the common ancestors of Carnivora about 40 million years ago. From about 15 million years ago, we can subdivide Canidae into three subgroups: fox-like animals, wolf-like animals and South American canids, such as the maned wolf and crab-eating fox. Members of the wolf-like group include wolves, coyotes and jackals, which are all closely related.

Observing the diversity of dogs and wild canids, scientists like Charles Darwin reasoned that different types of dogs might be descended from different types of wild canids. However, modern DNA analysis shows us that dogs are descended only from wolves.

Photos courtesy DAAC, MorgueFile, NPS, WSDOT and Wyoming.gov

In the next section, we'll look at how this evolution might have happened.

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