This is the process of organisms adapting to their environments over time.

Natural selection

Explanation:

Natural selection is a process in which organisms have certain genotypic traits that allow them to better adapt to their environment over some time. In natural selection, the genotypic traits help organisms to survive and reproduce. Those traits are also favored as they are preserved, multiplied and transmitted from generation to generation at the expense of less beneficial traits.

sex cells are usually half's then they find another half and make a fertilize egg