Final answer:
Charles Darwin is renowned for his theory of evolution, which was outlined in his 1859 work 'On the Origin of Species' and supported by evidence of natural selection and fossil analysis.
Step-by-step explanation:
In regards to ethology, Charles Darwin is most famously known for his theory of evolution. Darwin's pivotal work, 'On the Origin of Species' published in 1859, lays out the framework for understanding the process of evolution through natural selection. This theory explains how species evolve over time due to variations that increase an individual's ability to compete, survive, and reproduce. Furthermore, Darwin's research provided substantial evolutionary evidence including various biological observations from his voyage on the HMS Beagle and the analysis of fossils that supported the gradual change of species over geological time.