Which cellular process contributes to the diversity of species

Answer is Meiosis.

Meiosis is the process by which most eukaryotic organisms form sex cells or gametes. During prophase of meiosis I, the homologous pairs of chromosomes cross over with each other and often exchange chromosome segments. This recombination creates genetic diversity by allowing genes from each parent to intermix, resulting in chromosomes with a different genetic complement. The exchange of chromosome segment between non-sisters chromatids forms new combination of genes on a chromosome can lead to new traits in offspring. The process helps increase the genetic diversity of a species.