The dog has been selectively bred over millennia for various behaviors,
sensory capabilities, and physical attributes. Dog breeds vary widely in
shape, size, and color. They perform many roles for humans, such as
hunting, herding, pulling loads, protection, assisting police and the
military, companionship, therapy, and aiding disabled people. Over the
millennia, dogs became uniquely adapted to human behavior, and the
human-canine bond has been a topic of frequent study. This influence on
human society has given them the sobriquet of "man's best friend".
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