Darwin sailed around the world in the a ship called the HMS Beagle. During his voyage, Darwin made observations of the animal life that lived in different environments (1). One of the most famous species that Darwin observed were the finches that lived on the Galapagos islands (2). Darwin observed that there were 13 different species of the finches that lived on the islands (3). He noted that the main difference amongst the finches on each island were the finch's beak shape (4). He also observed that the finches on each island had beak shapes that were applicable for the type of food that was available on that island (5).
Darwin made similar observations throughout his journey. For example, Darwin observed that there are varieties amongst members of a population of a species (6). He observed that traits can be inherited (or passed on) from parent to offspring (7). He also observed that these populations produce more offspring than an environment can sustain (8). He observed the lack of resources causes competition within the population (9). Darwin observed that, due to the lack of resources within the environment, many offspring do not survive (10). Finally, Darwin observed that the offspring that have traits most advantageous for the environment are the ones that do survive (11).
These observations lead Darwin to develop the theory of evolution via natural selection.