Final answer:
Charles Darwin used the term 'descent with modification' to describe the evolutionary process where species change over time. It's a core concept of his theory of natural selection, which is mistakenly associated with 'survival of the fittest,' a term coined by Herbert Spencer.
Step-by-step explanation:
The phrase Charles Darwin used to indicate that every species has descended from preexisting species, and that each species has changed over time, is referred to as descent with modification. This term embodies the idea that species evolve over time through natural selection, where traits that provide a survival or reproduction advantage are more likely to be passed down through generations. This leads to the adaptation and evolution of species.
It is important to clarify that although survival of the fittest is often associated with natural selection, this phrase was actually coined by Herbert Spencer and not by Darwin himself. Nonetheless, it is closely related to the concept of fitness, where the fittest organisms are those most suited to their environment, thus more likely to survive and reproduce.