'$A$ brief reduction in size of a population,due to natural calamities,usually leads to random genetic drift'. For this statement,identify the correct example from the following.

The main basis of Neo-Darwinism is:

What is the variation of traits among members of the same species called?

Identify $P, Q,$ and $R$ in the following descriptions of natural selection types:
$P -$ More individuals acquire peripheral character values at both ends of the distribution curve.
$Q -$ More individuals acquire mean character value.
$R -$ More individuals acquire value other than the mean character value.
$\quad\quad P \quad\quad\quad Q\quad\quad\quad R$

$A$: $A$ single large mutation called saltation can produce new species.
$R$: Mutations are directional.

As a result of the excessive use of herbicides and pesticides,which types of varieties were selected in a short period?