Oogamy

[1] Oogamy is a common form of anisogamy, with almost all animals and land plants being oogamous.

Oogamy is found in most sexually reproducing species, including all vertebrates, land plants, and some algae.

The ancestral state of sexual reproduction is believed to be isogamy, with oogamy evolving through anisogamy.

Once oogamy evolves, males and females typically differ in various aspects.

[11][4]: 309 [12] When oogamy has evolved, males and females typically differ in many aspects.