$I.$ Use and disuse of organs
$II.$ Inheritance of acquired characters
$III.$ Branching descent
$IV.$ Natural selection
$V.$ Mutation
$VI.$ Reproductive isolation
The two key concepts of Darwinism from the given options are
$I$ and $II$
$III$ and $IV$
$V$ and $VI$
$IV$ and $VI$
Branching descent is one of the key concepts of
How Biological evolution has taken place ?