8th April

Evidence for Organic Evolution

  • Second Best Evidence for Organic Evolution:

    • The Earth was once a supercontinent known as Pangea, composed of all the landmass combined millions of years ago.

    • The phenomenon of continental drift resulted in the separation of these continents.

    • Between the continents, oceans were present.

    • Different climates emerged on each continent, leading to distinctive flora and fauna in various regions.

Fauna Migration and Domination

  • Flora and Fauna Variability:

    • Example Animals in South America:

    • House, hippopotamus, rabbit, bear.

    • When North America merged with South America, the fauna from North America became dominant over that of South America.

  • Evolution of Prototherians and Eutherians:

    • Australia was part of Asia during the evolution of prototherians from reptiles.

    • At the time of separation from Asia, prototherians evolved into eutherians.

    • Eutherians, which are carnivorous and more intelligent, became dominant and began to prey on prototherians and metatherians (marsupials).

    • In Australia, however, eutherians are not dangerous; marsupials dominate in that ecosystem.

Adaptive Radiation

  • Adaptive Radiation:

    • Defined as the process leading to the formation of different species starting from a common ancestral stock and radiating into various geographical areas.

  • Examples of Adaptive Radiation:

    1. Darwin's Finch

    2. Placental Mammals

    3. Australian Marsupials

Darwin's Finches

  • Characteristics:

    • Darwin's finches showcase adaptive radiation and divergent evolution.

    • They demonstrate common ancestry and biogeographical distribution.

  • Charles Darwin's Observations:

    • During his voyage on H.M.S. Beagle, Darwin visited the Galapagos Islands.

    • He observed variations of the same type of bird displaying different beak shapes adapted to their habitat.

  • Observations After Returning to South America:

    • Similar birds were found in South America with similar variations reflecting their distinct feeding habits.

  • Conclusion:

    • When South America separated from Pangea, the Galapagos Islands formed(22), where seed-eating birds from South America evolved into various species due to differing food habitats:

    1. Insect-eating

    2. Cactus-eating

    3. Fruit-eating

    4. Vegetable-eating

Placental Mammals (PM) and Australian Marsupials (AM)

  • List of Placental Mammals:

    • Rabbit, Deer, Bear, Mole, Anteater, Mouse, Wolf, Squirrel, Lemur, Bobcat

  • List of Australian Marsupials:

    • Spotted Cuscus, Koala, Flying Phalanger, Mole, Wombat, Numbat, Tiger Quoll, Kangaroo, Bandicoot, Tasmanian Wolf

  • Key Note: The comparison emphasizes the diversity between placental mammals and marsupials, with each adapting uniquely to their environments.