Dogs and Humans Evolved Together? More Than Man's Best Friend

They're lovable, they're loyal as all get out and they're more than just man's best friend. In fact, a new study shows that dog's may have actually played a big part in humans' evolutionary journey.

The study shows that dogs split from gray wolves about 32,000 years ago, and since then, domestic dogs' brains and digestive organs have evolved in ways that are very similar to the brains and organs of humans.

These findings may indicate that a more ancient origin for dog domestication than was previously suggested hit at a common environment that drove both these mammals and humans to evolve thousands of years ago.

"As domestication is often associated with large increases in population density and crowded living conditions, these 'unfavorable' environments might be the selective pressure that drove the rewiring of both species," according to researchers from the study.

While it isn't exactly clear when wolves earned the title of "man's best friend," a doglike skull was uncovered in the Siberian Mountains that suggests that the first dogs were domesticated around 33,000 years ago from gray wolves. However, genetic analysists suggest that dogs in China were domesticated only about 16,000 years ago.

DNA suggests that the gray wolves split off from the indigenous dogs about 32,000 years ago, according to researchers.

"Chinese indigenous dogs might represent the missing link in dog domestication," the researchers note.

Since then, dogs' evolution has been gradual, and there were no sharp decreases in the dog population over time, suggesting dogs gradually became domesticated, after many years of scavenging from humans.

The team then compared corresponding genes in dogs and humans. They found both species underwent similar changes in genes responsible for digestion and metabolism, such as genes that code for cholesterol transport. Those changes could be due to a dramatic change in the proportion of animal versus plant-based foods that occurred in both at around the same time, the researchers said.

The team also found co-evolution in several brain processes - for instance, in genes that affect the processing of the brain chemical serotonin. In humans, variations in these genes affect levels of aggression.