Conversation so far:
What is Darwin's theory in a nutshell?
Darwinism is a theory of biological evolution developed by the English naturalist Charles Darwin (1809–1882) and others, stating that all species of organisms arise and develop through the natural selection of small, inherited variations that increase the individual's ability to compete, survive, and reproduce.

Question: How was it developed
Self-contained rewrite: How was Darwin's theory developed?