What was one of the significant observations made by Charles Darwin during the HMS Beagle voyage?

One of the significant observations made by Charles Darwin during his voyage on the HMS Beagle was that organisms on islands vary from mainland species. This observation was crucial in forming the basis for his theory of evolution. Darwin noticed that the species he encountered on the Galápagos Islands were closely related to those found on the South American mainland, yet they exhibited distinct differences. This was especially evident in the finches, which had evolved various beak shapes adapted to different food sources on the islands.

This variation led Darwin to conclude that species were not fixed and unchangeable; instead, they adapted over time to their environments. His insight into how geographical separation can lead to divergence in species played a foundational role in the development of his ideas about natural selection and the evolution of species in response to environmental pressures.