What developmental process did Darwin emphasize as a mechanism for species change?

Darwin emphasized natural selection as a key mechanism for species change. Natural selection is the process through which certain traits become more common in a population because they contribute to improved survival and reproductive success in a particular environment. This occurs as individuals with advantageous traits are more likely to survive and reproduce, passing those traits on to the next generation. Over time, this leads to the adaptation of species to their environments and can result in the emergence of new species.

While adaptation is important in the context of natural selection, it is a consequence rather than the mechanism itself. Evolutionary migration and genetic drift are also concepts related to species change but do not capture the essence of Darwin's theory as thoroughly as natural selection does. Natural selection directly explains how advantageous traits are preserved and accumulated in a population, driving the process of evolution.