The evolution of species is based upon sum total of the species adaptive changes preserved by

Basic unit of evolution is

$A$ : Many countries have banned the use of antibiotics in the cattle feed.
$R$ : Dairymen give antibiotics in the feed to the cattle and it becomes breeding grounds for the antibiotic resistant bacteria

Replacement of original hard parts or even the soft tissues of the organisms by minerals is known as

Assertion : Comparative biochemistry provides a strong evidence in favour of common ancestory of living beings.

Reason : Genetic code is universal.

Louis Pasteur by careful experimentation demonstrated that/the