Evidences from Geographical Distribution

Biogeography is the study of the geographical distribution of plants and animals on Earth. It provides strong evidence for evolution by studying how continental shifts affected species survival and adaptation.

According to Wagner’s continental drift theory, Earth was once a single landmass called Pangaea. Due to tectonic plate movements, it broke apart into six major biogeographical realms, separated by oceanic barriers.

As these continents drifted apart, plants and animals in each realm evolved independently due to different environmental conditions.

The separation of continents explains the unique survival of certain species.

• The Concept: Australia was once connected to Asia but broke away during the Cretaceous period.
• The Result: It separated before carnivorous placental mammals evolved.
• Evolutionary Impact: Without placental carnivores to hunt them, monotremes (egg-laying mammals) and marsupials (pouched mammals like kangaroos) flourished in Australia, while they went extinct in many other parts of the world.

The Galapagos are volcanic islands about 1,000 km off the coast of South America, considered a "living museum" of endemic (unique) species.

• Darwin's Finches: Charles Darwin observed nearly 20 varieties of small black birds (finches) on these islands.
• The Mechanism: A single species of seed-eating finch migrated from the South American mainland to the Galapagos.
• Adaptive Radiation: Once on the islands, these original finches adapted to different food sources (like insects) across various island habitats. Over time, their beak shapes and sizes changed to match their new diets, evolving into completely new species.

Adaptive Radiation is the evolutionary process where a single ancestral species diverges into multiple new forms to adapt to different environmental niches.

The Concept: Closely related species are found in widely separated geographic areas, with no representatives in the intervening lands.

The Cause: These species likely had a widespread global distribution in the past, but environmental changes caused intermediate populations to go extinct.

Example: Lungfishes. Three genera are found on three completely isolated continents:

• Protopterus (Africa)
• Neoceratodus (Australia)
• Lepidosiren (South America)

The Concept: Some organisms are restricted to a very specific, limited geographical area and are found nowhere else on Earth.

Example: Prototherians (egg-laying mammals) are restricted entirely to the Australian realm.

• Biogeography studies the geographical distribution of plants and animals and provides evidence for evolution through patterns of similarity and difference across regions.
• According to continental drift theory, all continents were once united as Pangaea, and their separation led to the formation of distinct biogeographical realms.
• Isolation of continents by seas and barriers caused independent evolution of flora and fauna in different regions.
• The dominance of marsupials in Australia shows evolution in isolation due to the early separation of the continent from others.
• Adaptive radiation occurs when organisms diversify into different forms in isolated environments, as seen in island ecosystems.
• Darwin’s finches of the Galapagos Islands provide strong evidence of evolution, showing diversification from a common ancestor due to adaptation to different ecological niches.