Dawkins begins with humans and moves outwards through successively larger groups:
primates, and then the encircling groups that include
placental mammals,
marsupials,
monotremes,
chordates,
animals,
eukaryotes and
prokaryotes until arriving at the
origin of life. "The Farmer's Tale" tells of the
Neolithic Revolution, when humans domesticated plants and animals through
artificial selection. "
Eve's Tale" introduces
mitochondrial DNA, used to trace matrilineal ancestry. "The
Chimpanzee's Tale" is about
comparative genomics, specifically the comparison of
human and
chimpanzee genomes. "The
Gibbon's Tale" is about
phylogeny and introduces themes that run throughout the book.
Biogeography is a theme illustrated by "The
Sloth's Tale".
Charles Darwin and
Alfred Russel Wallace, who independently discovered the engine of evolution, recognized patterns in the geographic distribution of species, such as that oceanic islands have
endemic birds but not mammals (bats are the exception that proves the rule).
Alfred Wegener's theory of
plate tectonics provided the missing pieces of the puzzle. Multiple independent lines of evidence point to the continents having split from the ancient super-continent
Gondwana. After South America split from Gondwana, sloths and other
Xenarthrans evolved in "splendid isolation". After Australia split off, it was an ark carrying
marsupials. In this isolated environment, many marsupials evolved to fill niches occupied by placental mammals on other continents.
Convergent evolution is a theme, illustrated by "The
Marsupial Mole's Tale". The marsupial mole is not a mole, but resembles one as it has evolved to fill a similar niche. Many Australian marsupials mirror placental mammals on other continents. "The
Galápagos Finch's Tale" is about
natural selection and how it can produce rapid evolutionary change. Similarly, "The
Peacock's Tale" is about
sexual selection and how it can lead to
rapid evolutionary change. Other Tales are about peculiar features of their subjects. "The
Duckbill's Tale" is about its
electroreception and "The
Axolotl's Tale" is about
neoteny. (A humorous aside to the former is "What the
Star-Nosed Mole Said to the Duck-Billed Platypus".) "The
Ragworm's Tale" is about the evolution of
left-right symmetry. Dawkins discusses the
evolution of eyes, which all develop under the control of the same genes, despite their very different structures in groups such as
insects and mammals. Eyes have convergently evolved several times, as Dawkins discusses in "The Forty-Fold Path to Enlightenment" in
Climbing Mount Improbable. "The
Choanoflagellate's Tale" is about the evolution of
multicellularity. Choanoflagellates can form temporary colonies from a free-living unicellular stage.
Sponges have choanocytes, cells that resemble single-celled choanoflagellates, suggesting how multicellularity evolved. "The
Mixotrich's Tale" is about symbiosis.
Mixotricha paradoxa has bacteria, specifically
spirochaetes, which serve
Mixotricha as galley slaves in place of cilia to propel itself.
Mixotricha is a symbiont, helping its hosts digest cellulose. It lives only in the termite
Mastotermes darwiniensis. The "''
Rhizobium's'' Tale" is about the evolution of the
bacterial flagellum, likely from a
Type II secretion system. Despite the diversity of animal body plans,
wheels seem only to have evolved once. "The Great Historic Rendezvous" is the origin of eukaryotic cells.
Mitochondrion and
chloroplasts have their own DNA and divide by
binary fission, like bacteria.
Lynn Margulis's
endosymbiotic theory surmised that this is because they are descended from free-living bacteria. ==Reception==