Darwin went on a voyage aboard the HMS Beagle to the Galapagos Islands where he observed that species on different islands had slight differences that helped them survive in their environments; after returning home, he published On the Origin of Species which introduced his theory of evolution by natural selection, wherein organisms better suited to their environment are more likely to survive and pass on their traits, while less suited organisms die off.

1. Chapter 15 Darwin’s Theory of Evolution By James & Erik