It is often believed that for complex organisms such as animals, sexual reproduction is a must to produce offspring. Asexual reproduction is common in bacteria and (some) plants, but even tiny beings such as insects use sexual reproduction to produce a mass of variable offspring.
However, it has been found that despite having two clear sexes – male and female – there are cases where a certain species is able to reproduce without the need of sexual intercourse. In these cases, the female’s eggs spontaneously divides to form a new offspring without being fertilised by a sperm. Furthermore, sometimes the egg either fuses with another egg or undergo several genetic mixing and mutation to produce some variety in genetic pool, thus avoiding the issue of asexual reproduction (where the entire population can be wiped out by a single disease due to identical genetic makeup). This is known as parthenogenesis, and it has been documented in many insects, fish, reptiles and even birds.
Obviously, as there is no donation of a Y chromosome, every offspring born from parthenogenesis is female. Because of this, some species such as the New Mexico whiptail, a lizard that is capable of both sexual reproduction and parthenogenesis, the population has completely rid itself of males, making it a completely female species. Curiously, they still engage in “mock sex”, giving them the nickname “lesbian lizards”.
Although parthenogenesis has never been documented in mammals in nature, it has been induced artificially in mice, rabbits and monkeys. However, they all developed severe developmental issues due to the numerous mutations in the egg required for parthenogenesis.
But if in the future, human parthenogenesis is perfected, it is possible that humanity too could end up as an all-female society.