Final answer:
The principle of uniformitarianism states that the same natural laws and processes that operate in the present also operated in the past. It was popularized by geologist Charles Lyell and is relevant to the understanding of natural selection in biology.
Step-by-step explanation:
The principle of uniformitarianism in biology states that the same natural laws and processes that operate in our present-day observations also operated in the past and apply everywhere in the universe. This principle is often summarized as 'The present is the key to the past.' It was popularized by geologist Charles Lyell in the nineteenth century, who argued that the same geological processes that occur today have also shaped the Earth's surface in the past.
Regarding the options given, option d is the closest to being correct. While Darwin did not directly apply uniformitarianism to living things, the idea that slow and subtle processes can produce substantial change in geology is consistent with Darwin's hypothesis of natural selection in biology.