The Ancestor's Tale: A Pilgrimage to the Dawn of Life is a popular science book by the evolutionary biologists Richard Dawkins and Yan Wong. It retraces the history of life in reverse chronological order: A growing band of species meet their most recent common ancestors (concestors) at 40 rendezvous points. First published in 2004, it was updated in 2016 to reflect recent discoveries. Many reviewers described it as Dawkins's magnum opus.
Background
The book is patterned on Geoffrey Chaucer's The Canterbury Tales, in which pilgrims en route to Canterbury converge with other travelers and tell tales. Here, species convene with their common ancestors, and "Canterbury" is the origin of life.
The epigraph is from Mark Twain: "History doesn't repeat itself, but it rhymes." The authors argue that "Evolution rhymes, patterns occur. And this doesn't just happen to be so. It is so for well-understood reasons: Darwinian reasons, mostly, for unlike human history or even physics, biology already has its grand unifying theory." They note that no living species is ancestral to any other, but that all share a common ancestor. Evidence for this fact is that the code for translating genes into proteins is universal. Since genes and proteins are more similar in closely related species, they act as molecular clocks that show us when species split. The authors use concestor, coined by Nicky Warren, to describe the most recent common ancestor at each rendezvous point. The pilgrimage proceeds through extant species, with the exception of early hominids like Homo habilis, and species like the dodo, whose DNA is available to us.
The book was revised in 2016. Notably, "The Denisovan's Tale", about paleogenetics, replaces "The Neanderthal's Tale" and "The Sloth's Tale", about biogeography, replaces "The Armadillo's Tale". "The Galápagos Finch's Tale", about natural selection, includes new research on the genetics of Darwin's finches, and the conclusion of "The Elephant Bird's Tale" has been updated. The phylogenetic trees in the second edition are based on OneZoom evolutionary mapping software. In 2005, on a pilgrimage to the Galápagos, Dawkins wrote three new tales. The third is reprinted in the second edition.
Tales All Humankind Rendezvous point New Pilgrim Tale All Humankind The Tasmanian's Tale is about the identical ancestors point, from which all living people trace exactly the same set of ancestors. The authors look at the small, isolated population of Tasmania and the last surviving native Tasmanian, Truganini. They point out that she and all humans alive today share a recent common ancestor. The Farmer's Tale is about the Neolithic Revolution. Agriculture began when humans domesticated plants and animals through artificial selection. The Cro-Magnon's Tale is about cultural evolution. The authors note that “Archaeology suggests that something very special began to happen to our species around 50,000 years ago.” After Jared Diamond, they call this the Great Leap Forward.
Archaic Homo sapiens Rendezvous point New Pilgrim Tale Archaic Homo sapiens Eve's Tale is about coalescent theory. The authors introduce mitochondrial DNA, which is inherited from the mother and allows us to trace matrilineal ancestry (in humans, to Mitochondrial Eve). In mammals, the Y-chromosome is inherited from the father, and allows us to trace patrilineal ancestry (in humans, to Y-chromosomal Adam.) They introduce haplotypes. The Denisovan’s Tale is about paleogenetics, specifically Svante Pääbo’s work on Neanderthals and the sequencing of mitochondrial Denisovan DNA in 2009. The Ergast's Tale is about paleontology, how fossils form and how fortunate we are that they exist. They discuss significant fossils in human evolution, from Kamoya Kimeu’s discovery of Turkana Boy to Mary Leakey’s discovery of the Laetoli footprints. The Handyman's Tale is about brain-body mass ratio, and how Homo habilis acquired a high one. The authors introduce logarithmic scale and scatterplot, tools they return to. Ardi's Tale is about how hominids evolved bipedalism, citing work by Jonathan Kingdon. Nonhuman Primates Rendezvous point Time New Pilgrim Tale 1 6 mya Chimpanzees The Chimpanzee's Tale is about comparative genomics, specifically the comparison of human and chimpanzee genomes. The authors note that human chromosome 2 formed from a recent fusion, which is why the other Great Apes have 24 pairs of chromosomes and humans have 23. The Bonobo's Tale is about incomplete lineage sorting. 2 7 mya Gorillas The Gorilla's Tale is about human's changing attitude towards the great apes, ending with a discussion on racism, speciesism and the Great Ape Project. 3 14 mya Orangutans (Pongo) The Orangutan's Tale is about parsimony and its use in cladogram construction. They discuss the possibility that the ancestors of the Great Apes were in Asia, where one line stayed and gave rise to Orangutans, where they are found today (Orang utan is Malay for "man of the forest".) The other line went to Africa and gave rise to Gorillas, Chimpanzees and humans. They find this more parsimonious than the alternative. 4 18 mya Gibbons (Hylobatidae) The Gibbon's Tale is about phylogenetics. The authors note that the genetic code is degenerate. As a result, “some DNA codes are synonymous: they specify exactly the same amino acid.” Synonymous substitutions are invisible to evolution but not to biologists. Since they are not subject to selection, they show greater variation between species. The same is true of pseudogenes. Coding regions are conserved sequences. Rare genomic changes are unlikely to have arisen independently, and are likely due to common descent. 5 25 mya Old World monkeys (Cercopithecidae) Old World monkeys, being in the same Catarrhini clade as apes, are closer cousins to apes than to New World monkeys. Old World monkeys are sometimes called the 'tailed apes'. It is not known if the actual common ancestor had a tail or not. 6 40 mya New World monkeys (Platyrrhini) The Howler Monkey’s Tale is about gene duplication and how it creates new genes. When a gene is copied, it can evolve a new function. This happened in the evolution of color vision in primates. Old World Primates (including humans) are trichromats, with three opsins (red, green and blue), each coded for by a specific gene. The red and green opsin genes are similar, and adjacent on the X chromosome. They are derived from a recent duplication. Mutations that improved the function of the new gene were selected for until the opsin could detect a different wavelength.
Most New World monkeys are dichromats, with either red or green genes on the X chromosome. In some species, both red and green alleles are present in the population as a polymorphism. In Howler monkeys, both genes were put on the X chromosome through a translocation. As often happens in evolution, the same end was reached via different means. 7 60 mya Tarsiers The Tarsier's Tale is about its enormous eyes. Unlike most nocturnal mammals, they lack a tapetum lucidum to reflect light from the back of the eye for a second exposure on the retina. The ancestor of the tarsier was a diurnal animal which lost the tapetum lucidum. 8 65 mya Lemurs and Bushbabies The Aye-Aye's Tale is about island ecology. In Madagascar, a small strepsirrhine founding population evolved to fill available niches. Today, it is home to as many as one hundred species of lemur. Lemurs, kin to lorises and pottos, are found only on this island. Madagascar is also home to six of the world’s eight species of baobabs. With a landmass 1/1000 of Earth's total land area, it accounts for 4% of all species of flora and fauna.
Non-primate mammals Rendezvous point Time New Pilgrim Tale 9 70 mya Colugos The Colugo's Tale is about how genetic evidence has made people rethink existing phylogenies. A case in point: in the earlier edition, colugos and treeshrews joined humans at the same point. But genetic evidence from indels suggests that these creatures (colloquially called “flying lemurs” due to their patagium) are closer cousins to primates than to treeshrews. 10 70 myaTreeshrewsTreeshrews look like squirrels, but the resemblance is superficial. 11 75 myaRodents and Rabbitkind (Glires, Supraprimates or euarchontoglires)Rodents outnumber all other mammals by individuals and have been carried to every corner of the earth. They include dormice, pikas, squirrels.The Mouse's Tale is about developmental biology. Mice and humans have about the same number of genes, many of them the same. The developmental differences are due to differences in gene expression. Some genes code for transcription factors that regulate the expression of other genes. Borrowing from Matt Ridley, the authors liken genes to words, which can be put together in very different ways. From a similar vocabulary, very different books can be written. From a similar set of genes, very different organisms can be made. The Beaver's Tale is about Dawkins's concept of The Extended Phenotype. An organism's phenotype is typically defined as its physical traits, coded for by its genotype. But beavers are hard-wired by evolution to build dams, so the dam could be considered an extension of its phenotype (so, by extension, could the beaver lake.) 12 85 mya LaurasiatheresAn extremely diverse group of 2,000 species join here, including Carnivora (dogs, cats, bears and seals), Perissodactyla (horses, zebras, tapirs and rhinos), Cetartiodactyla (deer, giraffes, cattle and pigs), Chiroptera (bats), Insectivora (moles and shrews). They are grouped together based on similar gene sequences and are named for the northern super-continent of Laurasia, where they evolved.The Hippo's Tale is about cetacean evolution. All cetaceans, including whales, dolphins and porpoises, are descendants of land-living mammals of the Artiodactyl order, as evidenced by their vestigial pelvic and leg bones, by fossils such as Pakicetus and Basilosaurus and the fact that they have to come to the surface to breathe air. Like all mammals, they produce milk and, like most mammals, live young. The surprise is that whales are the closest living relatives of hippos. So close is the molecular resemblance that whales are now grouped with hippos as Cetartiodactyla. The Seal's Tale is about Fisher's principle. A sex ratio of 50:50 (males to females) is found in most animals. R. A. Fisher found that if females are less common than males, females will have a reproductive advantage. A tendency to produce females will be favored, until females are more common. The same is true if the sexes are reversed. A 50:50 ratio is evolutionarily stable. In a harem-based (polygynous) system such as that of elephant seals, where 4 per cent of males account for 88 per cent of all copulations, the 50:50 sex ratio seems to produce an excess of males. Fisher would note that, while a male is less likely to reproduce, if he does, he will do so in spades. The 50:50 ratio is still evolutionarily stable. 13 90 mya Xenarthrans and AfrotheresXenarthrans (from the Greek for "strange joint") include sloths, anteaters and armadillos. Afrotheres include elephants, elephant shrews, dugongs, manatees, hyraxes and aardvarks. Afrotheres are found in Africa and Xenarthrans in the Americas, for reasons that will become clear.The Sloth's Tale is about biogeography. Charles Darwin and Alfred Russel Wallace, who independently discovered the engine of evolution, recognized patterns in the geographic distribution of species. Darwin, during the Voyage of the Beagle, wondered: Why do oceanic islands have endemic species of birds but not mammals? (Bats are the exception that proves the rule.) Why are those species so similar to those on the nearest mainland? Why are some species specific to certain continents? Why are sloths (including ground sloths, fossils of which Darwin found) only in the Americas? These patterns occur the world over, as Wallace found in the Malay Archipelago.