Final answer:
Darwin's two principles of evolution are the inheritance of varied traits among individuals and the struggle for existence due to limited resources leading to natural selection.
Step-by-step explanation:
Charles Darwin suggests two main principles about how evolution works, which are central to his theory of natural selection. The first principle is that traits vary among individual organisms within a population, and these variations are inherited from parents to offspring. The second principle posits that more offspring are produced than can survive due to limited resources, leading to competition and a struggle for existence. Offspring with favorable inherited traits are more likely to survive and reproduce, thus passing those advantageous traits to the next generation. Over time, this process results in populations changing and adapting to their environments, a process Darwin termed 'descent with modification.'