Skip navigation

4.4.4. Biogeographic evidence of evolution

Biogeographic evidence of evolution

It is common to find more or less similar species, with a high degree of kinship, that live in places that are related to each other due to their proximity or characteristics. For example, on islands where each species has adapted to the specific conditions of each island. All these species come from a common ancestor, but as they adapted to the conditions of each place, they evolved and originated different species.

Some of these biogeographic evidence are:

  • On the Galapagos IslandsDarwin discovered fifteen different but closely related species of finches. All of these species are the same size (10-20 cm), but differ in beak shape and size. Each type of beak is adapted to the different food source that predominates on each island and to which they have adapted.

Cada especie de pinzón tiene un pico adaptado a la alimentación de cada isla

By John Gould (Darwin's finches.jpeg) [Public domain], via Wikimedia Commons

  • Some large running birds, such as the South American rhea, the African ostrich, and the Australian emu are quite similar, despite being at great distances. This is explained because they had a common ancestor who lived in the southern hemisphere of a supercontinent. When it fragmented, the different birds evolved independently.
  • Australia, separated from the rest of the continents about 70 million years ago, has a very different fauna and flora. Marsupial mammals like the kangaroo and koala are only found here. Mammals with placenta only appeared when they were introduced by humans. This explains that placental mammals appeared on the other continents after Australia had separated from them. The placentates replaced the marsupials for having a more efficient reproductive system.

In short, biogeographic evidence for evolution is based on the geographic distribution of species. When organisms live together they evolve in the same way, but when some populations are isolated, they evolve differently into different species.