In total, over a hundred different invented animal species are featured in the book, described as part of fleshed-out fictional future ecosystems.

Ecology and evolutionary theory are applied to create believable creatures, all of which have their own binomial names and text describing their behaviour and interactions with other contemporary animals.

[4] In this new period of the Cenozoic, which Dixon calls the "Posthomic", Europe and Africa have fused, closing the Mediterranean Sea; whereas Asia and North America have collided and closed the Bering Strait; South America has split from Central America; Australia has collided with Southern Asia (colliding with the mainland sometime in the last 10 million years), uplifting a mountain range beyond the mountains of the Far East that has become the most extensive and the highest chain in the world, greater even than the Himalayas at their zenith 50 million years ago; and parts of eastern Africa have split off to form a new island called Lemuria.

There are also more bizarre creatures such as the "raboons", gigantic theropod-esque descendants of baboons; the "night stalker", a gigantic predatory leaf-nosed bat native to Batavia; the "desert leaper", a giant kangaroo-like dipodid; and the "chiselhead", a descendant of the eastern gray squirrel that has evolved a wormlike shape and large incisors for chiseling into coniferous trees (hence its name).

Thinking of what might evolve to take their place if whales did go extinct eventually led to the idea of the giant aquatic penguins in the final book.

[1] One of few major speculative evolution works which preceded After Man, German zoologist Gerolf Steiner's 1957 Bau und Leben der Rhinogradentia, which included a complete fictional order of mammals (the "Rhinogradentia", or "snouters"), included some ideas similar to what was later featured in Dixon's work, such as an animal with a face mimicking a flower (also present on a future bat in After Man).

[5][7] The release of the new edition was celebrated with an event hosted at Conway Hall in London on 11 September that same year, which included a joint talk with Dixon and British paleontologist and science writer Darren Naish.

[5] A 40th Anniversary Edition of After Man was published by Breakdown Press in February 2022, featuring 18 additional pages of production material and previously unpublished sketches as well as a new afterword written by Dixon.

[11] Following the success of After Man, Dixon realized that there was a market for popular-level books which use fictional examples and settings to explain factual scientific processes.

The fact that Dixon created an entire fictional world, which was then made easily accessible through a book with color illustrations printed by mainstream publishing companies had a large impact and effectively laid the foundation of speculative evolution, which in recent years has been increasingly popular on the internet through various personal projects.

[12] Some of the animals featured in the book, in particular the popular "night stalker" (a giant and flightless predatory descendant of bats), have inspired numerous similar designs through speculative evolution projects since.

[5][10] To date, Dixon's 2010 speculative evolution book Greenworld, exploring humanity's impact on an alien ecosystem, has only been published in Japan.

The exhibition began with a "time tunnel", which visitors passed through before being met by several dioramas featuring the speculative future animals, including two full-size animatronic figures.