What are the 2 key concepts of Darwinian theory of evolution

What are the 2 key concepts of Darwinian theory of evolution. explain each concept with the help of a suitable example

Branching descent and natural selection are the two key concepts of Darwinian Theory of Evolution.

  1. Branching Descent:
    a. New species originate from a single common descendant.
    b. New species developed became adapted to a new environment through reproductive isolation.
    Example- Darwin’s finches - varieties of finches arose from grain eaters/Australian marsupials-evolved from common marsupial.

  2. Natural Selection:
    a. A process in which heritable variations enable better survival of a species to reproduce in large number.
    b. The essential variations in the characteristics are passed on from one generation to the next.
    c.These variations make them fit to survive in the constantly changing environment.
    Example- In an ecosystem, some giraffes have long necks and others have short ones. If something caused low-lying shrubs to die out, the giraffes with short necks would not get enough food. After a few generations, all the giraffes would have long necks.