Before babies are born, they grow either male sex parts or female sex parts.

Sexual reproduction first appeared about a billion years ago. Sexual reproduction is a process that can only be found in eukaryotes. There are other kinds of organisms (other than animals, plants and fungi), the other eukaryotes – such as the malaria parasite – that also engage in sexual reproduction.

Sex is used by plants and animals, and also by fungi and various single-celled organisms. A woman's ovum (egg cell) contains one X chromosome.

It usually needs two individuals which are different sexes from the same species. A man's sperm contains either an X or a Y chromosome.

In humans, males and females usually look different.

Some bacteria use conjugation to transfer genetic material between bacteria.