This idiom describes a ruthless, highly competitive environment where individuals prioritize their own success over others, often at great cost. It suggests a cutthroat, survival-of-the-fittest mentality, where loyalty or ethics may be sacrificed for personal gain. The phrase is used in business, politics, or social contexts to critique aggressive competition or moral compromise, carrying a harsh, cynical tone that reflects the brutality of such dynamics.

The phrase derives from the Latin proverb *canis canem edit* (‘dog eats dog’), recorded by Varro in the 1st century BCE, reflecting observations of animals and human greed. In English, it appeared by the 16th century, with Thomas Fuller’s 1732 *Gnomologia* noting ‘Dog will not eat dog’ to contrast human selfishness. The modern form, ‘dog eat dog,’ emerged in the 19th century, particularly in American English, during the rise of industrial capitalism. An 1854 *New York Herald* article used it to describe ruthless business practices. Its use grew in the 20th century, as seen in Upton Sinclair’s *The Jungle* (1906), reflecting economic and social Darwinism.