Law of the jungle
These days, usually signifies anarchy or lawlessness but this is not what Rudyard Kipling meant when he coined the expression in The Second Jungle Book in 1895. Kipling was referring to the Darwinian concepts of natural selection and survival of the fittest, whereby the predator, for example, will always catch the slowest gazelle, enabling surviving gazelles to breed faster, fitter progeny. Predators, on the other hand, also become faster and fitter enabling them to catch the slowest of the new breed of gazelles. Kipling’s Law of the Jungle, therefore, was evolutionary and balanced but this tends not to be how the expression is used today.