In a study released Friday, a team of archaeologists presented new evidence that horses were domesticated in 3500 B.C.—about a thousand years earlier than previous estimates. What was the first domesticated animal?
The dog. No one can pinpoint exactly when humans first started keeping dogs as pets, but estimates range from roughly 13,000 to 30,000 years ago. Archaeologists can tell domesticated canines apart from wolves through skeletal differences: Dogs had smaller teeth, for example, and a reduced "Sagittal crest"—the bone ridge that runs down the forehead and connects to the jaw. The earliest dog bones, discovered in Belgium in 2008, are from 31,700 years ago. But ancient dog skeletons have also been unearthed in western Russia, near its border with Ukraine, and elsewhere across Europe, Asia, and Australia, suggesting that canine domestication was a widespread phenomenon.
Scientists have also used DNA evidence to estimate the origin of domesticated dogs. The so-called "molecular clock" theory posits that if you know the speed at which DNA mutates, you can develop a chronology for doggie evolution. Say you know when wolves and coyotes separated and became different species, and you know what their genomes currently look like. You can then determine how long it took for those genetic changes to occur. Based on this methodology, dogs as a species are estimated to be 15,000 to 20,000 years old. But critics argue that gene substitution is not a constant process—it speeds up, then slows down—making the estimates rough at best.
How did dogs get domesticated in the first place? The first ones were basically just tame wolves. Some researchers believe wolves were first attracted by the garbage produced by early human settlements. Those canines brave enough to approach humans, yet not so aggressive as to attack, got fed. Eventually, they no longer needed the strong jaws and sharp teeth of their feral counterparts. Their noses got smaller, too. (Dogs characteristics can change a lot in only a few generations.) After this initial process of "self-domestication," humans started breeding dogs to help with hunting, herding, standing guard, and carrying stuff. Humans also deliberately bred dogs to be more adorable.
Other pets came later. Sheep and goats were first domesticated roughly 11,000 years ago, while cats became pets around 7000 B.C. with the advent of agriculture. (As people collected and stored grain, it would attract mice, which would then attract cats.) Around the same time, people started keeping cattle for consumption purposes. Several thousand years later, around 4000 B.C., as trade routes developed, humans began using oxen, donkeys, and camels to transport goods. Horses were eventually domesticated for both riding and carrying goods, but scholars differ on which purpose came first.
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Explainer thanks Richard Bulliet of Columbia University, James Serpell of the University of Pennsylvania, and Mary Elizabeth Thurston of Animal Image Photography.