How did the phrase It's a dog eat dog world originate?

I can imagine that it refers to the territorial behavior of many canine species. When two dogs (not domesticated, of course) fight for territory or something else, one of them usually dies. The phrase is pretty much derived from the competitive nature found in most wild dogs.

- Hametsu

“吃狗的狗世界”这个成语源自英语中的“it's a dog-eat-dog world”，意思是竞争非常激烈，弱肉强食。这个表达的来源不是很清楚，但据信它最早出现在19世纪的美国，可能源于对动物行为的观察，特别是狗在食物短缺时互相争斗的情况。这个表达后来被用来比喻人与人之间的残酷竞争。