Question

How do data from biogeography support he concept of common descent?

Answer 1

1. Historical Separation of Continents: Millions of years ago, Earth’s landmass existed as a single supercontinent called Pangaea. Due to tectonic movements, this split into separate continents (biogeographic realms). The isolation of species on these continents limited gene flow between populations, allowing independent evolution that reflects their unique evolutionary histories.
2. Distinct Biogeographic Realms: The Earth is divided into major realms (Nearctic, Palaearctic, Neotropical, Oriental, Ethiopian, Australian), each with distinct flora and fauna that evolved separately after continental drift. For example, marsupials are mainly found in Australia because the continent was isolated before placental mammals spread, allowing marsupials to diversify independently.
3. Similarity Supporting Common Ancestry: The flora and fauna of the Galapagos Islands closely resemble those of the South American mainland, indicating that the islands’ species descended from mainland ancestors and then diversified (adaptive radiation) in isolation.
4. Adaptive Radiation: Isolated species evolve to fill different ecological niches, as seen in Darwin’s finches of the Galapagos Islands, which exhibit diverse beak shapes adapted to different food sources. This diversity arising from a common ancestor is key evidence for descent with modification.
5. Geographical Barriers and Evolution: Seas, mountains, and deserts act as barriers to species dispersal, resulting in different evolutionary paths in different regions, consistent with descent from common ancestors confined by geography.