Content Warning: This section references racism and imperialism.

The adaptation of species to their environment is the single most important theme developed in The Voyage of the Beagle. Darwin’s observations during the five-year journey were essential to shaping his ideas about the evolution of species and the role of natural selection in driving biological diversity.

One of Darwin’s key insights is that different environments support different species, which evolve traits over time to suit their environment. Examples of this appear throughout The Voyage of the Beagle. In Argentina, for example, Darwin observes flamingoes feeding on small worms burrowing into seemingly inhabitable salt plains. Darwin is surprised to find such large birds living in such an inhospitable place, and he wonders how the worms they eat can survive in such salty mud. He notes that similar salt plains exist in Siberia and that flamingoes have been recorded feeding on small worms on those plains too. The similarity is too remarkable to be a coincidence; he writes, “As these circumstances, apparently so trifling, occur in two distant continents, we may feel sure that they are the necessary results of common causes. Well may we affirm that every part of the world is habitable!” (69).