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Pseudoextinction of a species occurs where there are no more living members of that species, but members of a daughter species or subspecies remain alive. As all species must have an ancestor of a previous species, much of evolution is believed to occur through pseudoextinction. However, it is difficult to prove that any particular fossil species is pseudoextinct unless genetic information has been preserved. For example, it is sometimes claimed that the extinct Hyracotherium (an ancient horse-like animal commonly known as an eohippus) is pseudoextinct, rather than extinct, because several species of horse, including the zebra and the donkey, are extant today. However, it is not known, and probably cannot be known, whether modern horses actually descend from members of the genus Hyracotherium, or whether they simply share a common ancestor.

Pseudoextinction, also called phyletic extinction, can sometimes apply to wider taxons than the species level. For instance, the entire Superorder Dinosauria is believed to have become pseudoextinct by many paleontologists, who argue that the feathered dinosaurs are the ancestors of modern day birds. Pseudoextinction for taxa higher than the genus level is easier to prove.

Some neoeugenicists, such as Gregory Stock argue that genetically engineered “designer babies” will ultimately lead to human pseudoextinction.

• Main articles: on Extinction, and the Cretaceous-Tertiary extinction event
• Human extinction

• Stock, G., 2003, Redesigning Humans: Choosing our genes, changing our future, Mariner Books ISBN 0-618-34083-1

• The Last Human - Excerpt from Redesigning HUMANS by Gregory Stock, envisaging the engineered evolution of modern humans into a posthuman form, and saying: "Such an occurrence would more aptly be termed a pseudoextinction, since it would not end our lineage. Unlike the saber-toothed tiger and other large mammals that left no descendants when our ancestors drove them to extinction, Homo sapiens would spawn its own successors by fast-forwarding its evolution."
• The difficulty of differentiating extinction from pseudoextinction in the fossil record
• The Extinction Website
• The Extinction Forum, part of The Extinction Website.

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