Final answer:
Charles Darwin arrived in Patagonia aboard the HMS Beagle as a naturalist during his five-year scientific voyage, which contributed to the foundation of his theory on natural selection.
Step-by-step explanation:
The individual who arrived in Patagonia aboard the HMS Beagle was Charles Darwin. Charles Darwin embarked on a significant scientific expedition on the HMS Beagle in 1831 at the age of 22, serving as its naturalist. Over the course of the five-year voyage, Darwin made critical observations and collected specimens from various locations worldwide, including Patagonia and the Galápagos Islands. His observations and collections, especially of the finches on the Galápagos, were vital to the development of his theory of natural selection, which would eventually be detailed in his seminal work, 'On the Origin of Species'.