Domestic dogs inherited complex behaviors, such as bite inhibition, from their wolf ancestors, which would have been pack hunters with complex body language. These sophisticated forms of social cognition and communication may account for their trainability, playfulness, and ability to fit into human households and social situations. These attributes have given dogs a relationship with humans that has enabled them to become one of the most successful species today.

The dogs' value to early human hunter-gatherers led to them quickly becoming ubiquitous across world cultures. Dogs perform many roles for people, such as hunting, herding, pulling loads, protection, assisting police and military, companionship, and, more recently, aiding disabled individuals. This influence on human society has given them the nickname "man's best friend" in the Western world. In some cultures, however, dogs are also a source of meat.

Wolves, and their dog descendants, likely derived significant benefits from living in human camps – more safety, more reliable food, lesser caloric needs, and more chance to breed. They would have benefited from humans' upright gait that gives them a more extensive range over which to see potential predators and prey, and better color vision that, at least by day, gives humans better visual discrimination. Camp dogs would also have benefited from human tool use, bringing down larger prey and controlling fire for various purposes.

Humans would also have derived enormous benefit from the dogs associated with their camps. For instance, dogs would have improved sanitation by cleaning up food scraps. Dogs may have provided warmth, as referred to in the Australian Aboriginal expression "three dog night" (a frigidly cold night). They would have alerted the camp to predators or strangers, using their acute hearing to provide an early warning.

It has been suggested that the most significant benefit would have been the use of dogs' robust sense of smell to assist with the hunt. The relationship between a dog's presence and success in the hunt is often mentioned as a primary reason for the domestication of the wolf, and a 2004 study of hunter groups with and without a dog gives quantitative support to the hypothesis that the benefits of cooperative hunting were an essential factor in wolf domestication.

The cohabitation of dogs and humans likely improved the chances of survival for early human groups. The domestication of dogs may have been one of the key forces that led to human success.

Characteristics of handwriting include:

1. The specific shape of letters, e.g. their roundness or sharpness

2. Regular or irregular spacing between letters

3. The slope of the letters

4. The rhythmic repetition of the elements or arrhythmia

5. The pressure to the paper

6. The average size of letters

7. The thickness of letters

Because handwriting is relatively stable, a change in the handwriting can be indicative of the nervousness or intoxication of the writer.

A sample of a person's writing can be compared to that of a written document to determine and authenticate the written document's writer; if the writing styles match, it is likely that one person wrote both documents.