Sexual reproduction arose as defence againist parasitism. It is normally obligatory among higher vertebrates. A new era of reproduction was inaugurated in 1996 by Dolly the Sheep. Confounding the received wisdom that a mammal could not be cloned, Ian Wilmut and his colleagues at the Roslin Institute in Edinburgh, Scotland, generated Dolly from the DNA of a specialised adult cell, not from an unspecialized embryonic cell. Dolly's chromosomes were taken from the mature udder cells of one sheep and injected into another sheep's egg cell from which the DNA had been removed. Thus Dolly was born without a father.

        Researchers have gone on to clone monkeys and many other species. Even therapeutic cloning is controversial. However, if identical twins had traditionally been known as identical clones, then then it is debtable whether the popular response to Dolly and her cousins would be quite so hysterical.

        In Brave New World, the family and sexual reproduction have been abolished in humans. Brave new worlders are made at the Hatching and Conditioning Centre. Up to ninety-six identical twins are produced from from a single egg, via a state-controlled process of fertilization, predestination, decanting and conditionining Bokanovsky Group: A group of identical twins created by dividing a single egg many times. This process is used only on Gammas, Deltas and Epsilons.