Dog

History and evolution
Domestic dogs inherited a complex social hierarchy and behaviors from their wolf ancestors. Dogs are pack hunters with a complex set of behaviors related to determining each dog's position in the social hierarchy, and they exhibit various postures and other means of nonverbal communication that reveal their states of mind. These sophisticated forms of social cognition and communication may account for their trainability, playfulness, and ability to fit into human households and social situations, and these attributes have earned dogs a unique relationship with humans, despite being potentially dangerous apex predators.
Although experts largely disagree over the details of dog domestication, it is agreed that human interaction played a significant role in shaping the subspecies. Shortly after domestication, dogs became ubiquitous in human populations, and spread throughout the world. Emigrants from Siberia likely crossed the Bering Strait with dogs in their company, and some experts suggest the use of sled dogs may have been critical to the success of the waves that entered North America roughly 12,000 years ago. Dogs were an important part of life for the Athabascan population in North America, and were their only domesticated animal. Dogs also carried much of the load in the migration of the Apache and Navajo tribes 1,400 years ago. Use of dogs as pack animals in these cultures often persisted after the introduction of the horse to North America.
The current consensus among biologists and archaeologists is that the dating of first domestication is indeterminate. There is conclusive evidence dogs genetically diverged from their wolf ancestors at least 15,000 years ago, but some believe domestication to have occurred earlier. It is not known whether humans domesticated the wolf as such to initiate dog's divergence from its ancestors, or whether dog's evolutionary path had already taken a different course prior to domestication. For example, it is hypothesized that some wolves gathered around the campsites of paleolithic camps to scavenge refuse, and associated evolutionary pressure developed that favored those who were less frightened by, and keener in approaching, humans.