With the discovery of DNA & its form of replication,
Neo-Darwnism could explain genetic variation in populations through chance
mutations ( mistakes in DNA replication) and recombination (mistakes in
the chromosomes during the formation of sperm & egg cells).
Evolution consists primarily of changes in the frequencies of alleles
(different forms of genes) between one generation and another.
Speciation occurs gradually
when populations are reproductively isolated by geographic barriers.