The core question investigated is how species originate and diversify through the mechanism of natural selection. Charles Darwin, a naturalist and geologist, synthesizes decades of observational data and experimental evidence to propose that organisms evolve over generations through the process of natural selection. He argues that individuals with advantageous traits are more likely to survive and reproduce, thereby passing those traits to subsequent generations, which leads to the gradual adaptation and divergence of populations.

Experts recognize this work as the foundational text of modern evolutionary biology. Readers frequently note the dense, academic nature of the 19th-century prose, which requires careful attention to follow the logical progression of Darwin's arguments.