What used survival of fittest for the first time?

The phrase "survival of the fittest" was popularized by the British philosopher Herbert Spencer in the 19th century, particularly in relation to his ideas on social Darwinism. However, it was Charles Darwin who initially introduced the concept of natural selection in his work "On the Origin of Species" published in 1859. Spencer's expression was used to describe the process of natural selection, emphasizing the competition for resources and adaptation in the evolution of species.