Final answer:
Facts supporting Darwin's theory include heredity, competition for limited resources, and variation among offspring. Darwin's observations during his voyage on the HMS Beagle, such as the Galápagos tortoises.
Step-by-step explanation:
What are the facts to support Darwin's theory of natural selection and descent with modification? Facts supporting these concepts come from Darwin's key observations and inferences. The first fact is rooted in heredity, where most characteristics of organisms are passed from parent to offspring. Secondly, there is the production of more offspring than can survive, leading to competition due to limited resources. The third fact involves the variation among offspring's characteristics, which are also inherited.
Darwin's insights came from his time on the HMS Beagle, where he observed variations in species like the Galápagos tortoises and finches. This led him to conclude that organisms with inherited traits better suited to their environment had higher survival and reproductive rates, which over generations, would lead to populations changing in their genetic composition—a process he termed descent with modification.
Furthermore, Darwin knew about artificial selection from breeding practices and inferred that a similar process occurs naturally. He defined 'fitness' as an organism's ability to survive and reproduce, with 'nature' selecting the most useful variations, hence natural selection. Ultimately, these principles suggest that beneficial traits become more common over time, with populations adapting to their environments. These concepts are the foundation of Darwin's argument for adaptive evolution.