In evolutionary terms, what does "survival of the fittest" refer to?

The phrase "survival of the fittest," coined by Herbert Spencer and often associated with Charles Darwin's theory of natural selection, refers specifically to how certain adaptations enhance an organism's ability to survive and reproduce in a given environment. This concept emphasizes that individuals with traits that are better suited to their environment are more likely to survive, reproduce, and pass those advantageous traits to the next generation.

Adaptations can be physical, such as increased speed for evading predators, or behavioral, like migration patterns that allow access to food. Over time, these adaptations contribute to the evolution of species, as those individuals best suited to their environment thrive and help shape the genetic makeup of future generations.

This understanding is key to grasping the mechanics of natural selection, where the term "fittest" does not solely denote physical strength, but rather encompasses a range of traits that improve an organism's chances of survival and reproductive success in its particular ecological niche.