Hello james,

The two key concepts of Darwin’s theory of evolution are:

1. Branching Descent

2. Natural Selection

Branching Descent

It is the process in which new species originate from a single ancestor. They became adapted to the new environment through reproductive isolation. For eg., Darwin’s finches which evolved from a single grain eater species.

Natural Selection

In this process, the variations in an individual facilitate better survival of species. They reproduce in large numbers. These variations are passed on to successive generations which help them to survive in the changing environmental conditions. For eg., few giraffes have long necks while others have short necks. If the low-lying shrubs are eliminated for some reason, the giraffes with short necks would be replaced by giraffes with long necks.

HOPE THIS WILL HELP YOU

GOOD LUCK