For all species of higher animals, reproduction requires the production of eggs but not necessarily the production of sperm  There are some species whose members are all female; the eggs produced by a rare female-only species of salamander hatch without fertilization
This has the drawback that all offspring have genetic codes nearly identical to that of the single parent, making the species less adaptive than species containing both male and female members
Some offspring of species of higher animals containing both female and male members have genetic codes more similar to one parent than to the other parent.