Generation 1 Generation 2 Generation 3 Generation 4

The diagram above represents an evolutionary path for a population of organisms. Each successive generation is indicated by number, with the oldest generation being Generation 1 and the youngest generations being Generation 4.

Which of the following pairs of generations likely have the most genetic differences between them?
A.
Generations 1 and 3
B.
Generations 2 and 4
C.
Generations 2 and 3
D.
Generations 1 and 4