Among humans, you can observe that there is variability in shape (size), skin color, and other traits. the variety in a small population results from in either sexual reproduction or meiosis.

Crossing over, independent assortment and random fusion of gametes

Explanation:

Sexual reproduction creates variations by any of the three processes:  

A) Exchange of genetic material between the non-sister chromatids of homologous chromosomes during prophase I of meiosis produce new gene combinations.

B) Independent assortment of homologous chromosomes towards opposite poles during anaphase I of meiosis I produce genetic variations among the daughter cells.

C) The random fusion of the gametes formed by meiosis further add genetic variations.