Introduction
You likely view evolution as a forward march from primitive microbes to modern humans. This linear perspective creates a false hierarchy with yourself at the pinnacle of life.
Richard Dawkins offers a reverse pilgrimage model in The Ancestor's Tale. You trace your ancestry backward in time, meeting other species at specific rendezvous points. This journey reframes humanity as just one twig on a vast evolutionary tree.
The book structures the history of life as a pilgrimage toward the origin. You travel backward through mammals, reptiles, fish, and single-celled organisms to meet the universal common ancestor.
- Which species shares your most recent common ancestor?
- How did diverse animals converge on similar bodily designs?
- Where do humans fit into the grand family tree of all living things?
1. Human Ancestry and Our Ape Relatives
You start the pilgrimage by tracing human ancestry backward through recent generations. In any isolated breeding population, tracing ancestry backwards quickly leads to a point where every individual is either a common ancestor to everyone or has no surviving descendants. Statistician Joseph T. Chang proved this using mathematical modelling and base 2 logarithms.
Applying the model to a population of 5,000 Tasmanian aboriginals yields a common ancestor in just over 12 generations, and universal ancestors in about 22 generations. Chang One marks the most recent common ancestor for the entire group. Chang Two marks the point where about 80 percent of individuals become universal ancestors to all future generations.
Tracing human ancestry backward reveals our closest common ancestors with chimpanzees, gorillas, orang utans, and gibbons, reframing humanity as one branch among modern apes.
Interbreeding between modern humans and Neanderthals left tangible genetic traces in non-African populations today. Whole-genome sequencing of ancient Neanderthal remains revealed that modern Eurasians inherited a small percentage of their DNA from Neanderthals, with gene flow predominantly from Neanderthals into expanding modern human populations. Svante Pääbo’s lab extracted genomes from a 40,000-year-old Croatian specimen and a 50,000-year-old Siberian Neanderthal woman, allowing researchers to identify shared single nucleotide polymorphisms. Modern Europeans average 1.2 per cent Neanderthal DNA, while modern Asians average 1.4 per cent. Adding all Neanderthal regions together from multiple people covers 20 per cent of the genome.
Chimpanzees and Bonobos
You reach Rendezvous 1 at 5 to 7 million years ago. Humans share a most recent common ancestor, Concestor 1, with common chimpanzees and bonobos from approximately 6 million years ago. Jane Goodall discovered termite fishing and intergroup warfare in common chimpanzees, while field studies noted nut-hammering traditions and the grooming hand clasp. Concestor 1 likely possessed traits intermediate between humans and apes, such as a chimpanzee-sized brain, hairiness, knuckle-walking tendencies, and stone tool usage for cracking nuts and termite fishing.
Gorillas and Asian Apes
Rendezvous 2 marks our meeting with gorillas in Africa around 8 million years ago, representing an exclusively vegetarian ape lineage. Gorillas differ from chimpanzees by being completely vegetarian and maintaining harem-based social structures led by dominant males. Dr Thomas Savage obtained a gorilla skull in Gabon in 1847, initially identifying it as a new species of orang and attributing to it an exaggerated reputation for ferocity.
Rendezvous 3 occurs at approximately 14 million years ago with the Asian orang utans, raising questions about whether our shared ancestor lived in Africa or Asia. While early Miocene apes blossomed in Africa, rich mid-to-late Miocene fossil evidence in Asia makes it plausible that the ancestor lived in Asia before later lineages evolved. Fossil genera such as Sivapithecus, Lufengpithecus, and Ouranopithecus populated the late Miocene landscape of Asia.
Rendezvous 4 brings you to gibbons. Gibbons are small apes specialized in high-speed brachiation, using their long arms and grasping hands to swing through tree canopies. Richard Dawkins explains that gibbons use arm-swinging locomotion called brachiation to traverse distances. They also possess bipedal walking skills along branches, using their arms purely to steady themselves. A gibbon can hurl itself across a sheer ten-metre gap in the canopy using powerful spring-loaded wrists.
2. Monkeys, Primates, and the Rise of Mammals
Rendezvous 5 marks the transition into the Palaeogene period at approximately 25 million years ago, where apes and Old World monkeys converge at Concestor 5. Old World monkeys are divided into two main subfamilies:
- the African colobus monkeys along with Asian langurs and proboscis monkeys;
- the mostly Asian macaques plus African baboons and guenons.
Concestor 5 likely possessed narrow downwards-facing nostrils characteristic of catarrhines. There are 130 species of Old World monkeys today. Around 14 million years ago, Old World monkeys greet their own common ancestor.
Victoriapithecus fossil fragments from Maboko Island in Lake Victoria help illuminate the fossil history of Old World monkeys.
New World Rafting
Around 40 million years ago, small African primates and rodents were carried across the shrinking gap between Africa and South America on floating islands of mangrove swamps or tangled trees driven by favourable currents and low sea levels, founding the entire New World primate and rodent populations from single rare immigration events. New World monkeys and hystricognath rodents reached South America from Africa via accidental rafting on floating vegetation massifs.
On 4 October 1995, at least 15 green iguanas unexpectedly appeared on the eastern beaches of Anguilla in the Caribbean, having arrived on a massive floating raft of logs and uprooted trees pushed out to sea by hurricanes Luis or Marilyn. Some logs in the rafting mat that carried green iguanas measured 30 feet. Around 40 million years ago is the approximate time of Rendezvous 6 and the origin of New World platyrrhine monkeys. Fossilised monkey teeth were unearthing in Peru in 2015. Squirrel-sized monkeys already existed in Amazonia by 36 million years ago.
At Rendezvous 7, approximately 60 million years ago, anthropoids split from tarsiers, uniting them into the haplorhine clade. Tarsiers form the sister clade to anthropoids within haplorhines, representing a lineage that reverted to a nocturnal lifestyle by evolving giant eyes instead of a tapetum lucidum. Modern tarsiers are nocturnal leapers that lack the reflecting tapetum lucidum found in other nocturnal mammals, compensating instead by growing enormous eyes that require them to rotate their entire heads nearly 360 degrees. Tarsiers can jump a maximum horizontal distance of 3 metres and a maximum vertical distance of 1.5 metres.
The fossil Archicebus achilles unearthed in China represents the earliest known branch of the tarsier line, featuring smaller, diurnal eye sockets and unfused lower leg bones unlike modern tarsiers.
Most living primates outside of haplorhines are strepsirrhines, dominated by lemurs that live exclusively in Madagascar. Accepted date for Rendezvous 8 is 65 million years ago. Strepsirrhines mean split nostril. The majority of surviving primates in this group are lemurs on Madagascar, while others include leaping bushbabies and creeping lorises and pottos. There are about 100 or so surviving lemur species in Madagascar and 32 species of loris and bushbaby families.
The author's childhood pet bushbaby named Percy was tiny enough to sit on a glass rim and drink whisky, but would urinate on the author from a mosquito net when not caught in time.
Madagascar acts as an evolutionary laboratory due to its ancient isolation, housing high endemism while lacking many standard African mammal groups. Madagascar separated from Africa about 165 million years ago and from India around 90 million years ago. Its terrestrial fauna largely stems from ancient Gondwana residents or rare lucky rafting events, completely missing animals like antelopes, zebras, giraffes, and cats. Madagascar houses 5 percent of world plant and animal land species and 80 percent of Madagascan species are found nowhere else on earth. Colonization dates for Madagascan Carnivores and rodents range from 20 to 25 million years ago.
Tenrecs arrived as a single founder population and diversified via convergent evolution into species resembling hedgehogs, shrews, and water shrews.
The Cretaceous Catastrophe
The Cretaceous-Tertiary boundary marks a catastrophic mass extinction driven by a meteorite impact that wiped out the dinosaurs and released mammals from ecological suppression.
A massive projectile impact near Yucatan created the Chicxulub crater and spread iridium dust worldwide, triggering global fires and a two-year nuclear winter. This event killed the dinosaurs and half of all marine species, allowing small shrew-like mammals to multiply. The K/T boundary forms a 66-million-year barrier separating mammals and dinosaurs. The Chicxulub impact crater measures 100 miles wide and 30 miles deep. The impact shockwave traveled around the planet at 1,000 kilometres per hour.
The Deccan Traps in India spewed extensive lava flows around the same geological timeframe, though the space projectile served as the final deathblow.
Three distinct models attempt to explain how mammals diversified following the K/T extinction event, with molecular and fossil evidence favoring the delayed explosion model.
- The Big Bang Model posits a single surviving Noah species branching rapidly right after the catastrophe.
- The Non-explosive Model suggests continuous branching before and after the K/T boundary without sharp discontinuities.
- The Delayed Explosion Model proposes that modern mammal lineages trace their separate roots deep into the Age of Dinosaurs as unspecialized shrews, exploding in diversity simultaneously only after the dinosaurs vanished.
Approximate age of Concestor 13 shared by shrews is 90 million years ago. Eurasian shrews and tenrec shrews remain very similar to each other because they haven't changed much since primitive times.
3. Laurasiatheres, Marsupials, and Monotremes
The pilgrimage widens to encompass diverse northern laurasiatheres, gliding rodents, swimming whales, pouch-bearing marsupials, and egg-laying monotremes.
Rabbits were once classified as rodents due to prominent gnawing teeth. Today, taxonomists place them in Lagomorpha while grouping them with rodents in the Glires cohort. Rodents account for more than forty per cent of all mammal species and are more numerous than all other mammals combined.
Rats and mice have traveled globally with humans, acting as vectors for major historical pandemics such as the Black Death and the Justinian plague.
At Rendezvous 11, occurring 75 million years ago, rodents and lagomorphs join your lineage. The mammalian genome functions not as a blueprint where each gene specifies a body part. It operates as a shared dictionary of words or a computer toolbox of subroutines. Mammals share roughly the same number of genes, around twenty thousand, because they use the same basic vocabulary for embryology.
Matt Ridley compares genes to the vocabulary of an educated native speaker, where different books like David Copperfield and The Catcher in the Rye use the same words in different orders.
Moving further back, Laurasiatheria unites a diverse group of northern-origin mammals that share a more recent common ancestor with each other than with humans. Taxonomists group these over 2,000 species of laurasiatheres into seven different orders based on molecular studies, despite outward differences.
Whales and Artiodactyls
Molecular evidence reveals that whales are not a separate ancient order. They are deeply embedded within even-toed ungulates, making hippos their closest living relatives.
Ernst Haeckel in 1866 presciently classified hippos as a tiny twig on the branch leading to Cetacea in his mammalian evolutionary tree.
Marsupials diverge from placental mammals primarily in their reproductive strategy involving a rudimentary placenta and an external pouch. Marsupial embryos are born at a very early stage, crawling through fur to clamp onto a teat inside a pouch, which acts as an external womb.
Australinean marsupials represent the vast majority of surviving marsupial species, having radiated extensively in isolation after arriving via South America and Antarctica.
Gondwana and Monotremes
Monotremes are the sole surviving representatives of the australosphenidan lineage of mammals that evolved in the southern continent of Gondwana. While all other living mammals descend from northern boreosphenidans, monotremes retain ancient traits such as laying leathery eggs and a cloaca.
The duck-billed platypus and short-beaked and long-beaked echidnas are the only three surviving genera of monotremes, yielding five species in total among the 5,500 species of living mammals that all have fur and suckle their young.
The platypus hunts underwater with its eyes, ears, and nostrils tightly closed by relying on an advanced electro-sensory system in its bill. It uses tens of thousands of electrical and mechanical sensors on its rubbery bill to detect weak electrical fields generated by the muscle contractions of its prey.
Jack Pettigrew and Paul Manger mapped the platypus brain, revealing a massive cortical representation of the bill known as the platypunculus.
4. From Reptiles to the Origin of Life
The final stretches of the journey cross amphibians, fish, invertebrates, fungi, and light harvesters down to the universal progenitor and the chemical origin of heredity.
Land Transition and Fish
Concestor 16 lived around 320 million years ago and represents the branching point where synapsids like mammals separated from sauropsids, which include modern reptiles, dinosaurs, and birds. Sauropsids are the largest contingent of land vertebrate pilgrims, outnumbering mammals significantly. They comprise lizard-like reptiles or lepidosaurs and dinosaur-like reptiles or archosaurs, the latter of which includes modern birds.
Concestor 16 lived during the Carboniferous period in vast swamps of giant club moss trees with an extensive ice cap at the South Pole.
Amphibians are closely related to amniotes but rely primarily on water or specialized moisture-retaining mechanisms for reproduction, whereas amniotes possess waterproof skins and eggs. While amniotes reproduce either viviparously or via tough-shelled waterproof eggs containing a private pond, most amphibians reproduce in water. Even tree-dwelling frogs have evolved methods such as nesting in wet foam produced by cooperative behaviors or storing eggs in back skin or vocal sacs.
Male African grey tree frogs cooperate to whip up a thick white foam that protects their eggs until tadpoles drop into puddles below, while South American marsupial frog females carry eggs under a layer of skin on their backs.
Lungfish are our closest living fishy relatives, sharing an ancient sarcopterygian ancestor and homologous lungs with land-dwelling tetrapods. Six surviving lungfish species live in freshwater across Australia, South America, and Africa. They retain the basic appearance of our shared common ancestor and use lungs to breathe air, either to withstand dry seasons by burrowing in mud or to supplement gills in oxygen-poor waters.
Captive West African lungfish have been observed using tassel-like fins to walk along the bottom of their tank.
Sharks and cartilaginous fish split early from bony vertebrates, possessing skeletons made of cartilage instead of bone, no swim bladders, and skin covered in dermal denticles. Because they lack a swim bladder, many sharks must swim continuously to maintain buoyancy, aided by urea retention in their blood and large oil-rich livers. Their teeth are evolutionarily modified dermal denticles.
The Miocene shark Carcharocles megalodon grew to three times the size of a great white shark with teeth as big as a human face, while modern deep-sea lantern sharks use bioluminescence for camouflage and communication.
Vertebrate evolution was marked by massive genetic novelty driven by two rounds of whole-genome duplication, known as the 2R hypothesis. Large chunks of the ancestral vertebrate genome were copied twice, resulting in a fourfold duplication of gene clusters such as Hox genes and multiple functional globins. This expansion created a massive difference in genome complexity between vertebrates and invertebrates.
Human alpha and beta globin genes on chromosomes 11 and 16 arose from a copy-and-paste duplication of an ancestral globin gene half a billion years ago.
Invertebrates and Microbes
The animal kingdom is deeply divided into two main subkingdoms, deuterostomes and protostomes, based on the embryonic event known as gastrulation. During gastrulation, the blastopore forms. In deuterostomes, the blastopore becomes the anus while the mouth appears later as a separate perforation. In protostomes, meaning mouth-first, the blastopore becomes the mouth or closes to form both openings.
Coral polypifers build massive underwater mountains over hundreds of thousands of years by depositing limestone skeletons on the remains of past generations. Coral success stems from an association with photosynthetic microscopic algae called zooxanthellae. Charles Darwin first explained how coral atolls and barrier reefs form through the continuous subsidence of the sea bottom matched by the upward growth of corals.
Darwin published his debut scientific book on Coral Reefs at age 33 after his voyage on the Beagle, explaining how fringing reefs turn into barrier reefs and atolls as land subsides.
Sponges are multicellular animals whose cells possess totipotency, meaning every single cell is capable of regenerating a complete new sponge. Sponges lack nervous systems, organs, and a distinct germ line, instead driving water currents through their bodies using specialized flagellated cells called choanocytes.
- Take a living sponge and separate its cells by forcing them through a fine piece of bolting cloth.
- Pass the disassembled cells into a saucer of sea water to form a sediment of crawling amoeboid cells.
- Allow the agglomerating cells to grow into whole new sponges.
H.V. Wilson demonstrated in 1907 that forcing a living sponge through a fine bolting cloth separated its cells into a red cloud that could re-aggregate and grow into a whole new sponge.
Fungi are genetically much closer to animals than they are to plants, functioning as absorptive organisms that spread extensive underground networks through their food source. Fungi belong to the opisthokonts alongside animals. Rather than hunting and digesting food internally, a fungus spreads a subterranean network of thread-like hyphae called a mycelium through its food source, secreting digestive enzymes and absorbing nutrients externally across a massive surface area.
Fairy rings form because the circular leading edge of an expanding mycelium enriches the soil with broken-down products of digestion, causing grass and fruiting bodies to grow more luxuriantly.
The Great Historic Rendezvous represents the evolutionary origin of the eukaryotic cell through the momentous merging of ancient host cells with engulfed bacterial cells. Chloroplasts evolved from engulfed photosynthetic cyanobacteria, and mitochondria evolved from oxygen-utilizing alpha-proteobacteria. These endosymbiotic bacteria retained their own reproduction mechanism and remnants of DNA while integrating into the metabolic machinery of complex eukaryotic cells.
Non-plant algae and dinoflagellates show multiple successive rounds of endosymbiosis by swallowing cells that had already swallowed photosynthetic cells.
The Origin of Life
The origin of life was fundamentally the origin of true heredity, which requires a replicator rather than mere metabolism or reproduction without inheritance. Fires exhibit reproduction without heredity because their variations are driven entirely by environmental fuel and wind rather than inherited traits from a parent spark. True heredity requires a replicator that forms lineages of copies where variants resemble their parents more than random members, sparking Darwinian natural selection.
Fires can spread and give birth to daughter fires on the wind, yet a blue or crackling fire does not inherit those specific traits from the initiating spark.
RNA can act as both a replicator and an enzyme catalyst, supporting the theory that an RNA world preceded DNA and proteins. Proteins make great enzymes but poor replicators, while DNA is a great replicator but a poor enzyme. RNA possesses structural traits allowing it to form short double helices and tie itself into knots like proteins, functioning as ribozymes. Sol Spiegelman demonstrated bare RNA evolution in test tubes.
Sol Spiegelman isolated Qβ RNA and its replicase enzyme in water with building blocks, and after 74 generations the RNA evolved into a streamlined fragment a fraction of its original size optimized purely for test-tube replication.
10 Key Ideas
- Joseph T. Chang proved using mathematical modelling and base 2 logarithms that tracing ancestry backwards in isolated populations quickly leads to universal common ancestors.
- Whole-genome sequencing of ancient remains revealed that modern Eurasians inherited a small percentage of their DNA from Neanderthals due to historical interbreeding.
- Mid-to-late Miocene fossil evidence in Asia makes it plausible that the shared ancestor of humans and Asian orang utans lived in Asia before later lineages evolved.
- New World monkeys and hystricognath rodents reached South America from Africa around 40 million years ago via accidental rafting on floating vegetation massifs.
- The Cretaceous-Tertiary boundary marks a catastrophic mass extinction driven by a meteorite impact that wiped out the dinosaurs and released mammals from ecological suppression.
- The mammalian genome functions not as a blueprint where each gene specifies a body part, but as a computer toolbox of subroutines sharing roughly the same basic vocabulary.
- Molecular evidence reveals that whales are not a separate ancient order, but are deeply embedded within even-toed ungulates, making hippos their closest living relatives.
- Concestor 16 lived around 320 million years ago during the Carboniferous period, representing the branching point where mammals separated from sauropsids like modern reptiles, dinosaurs, and birds.
- The Great Historic Rendezvous represents the evolutionary origin of the eukaryotic cell through the momentous merging of ancient host cells with engulfed bacterial cells that became chloroplasts and mitochondria.
- RNA can act as both a replicator and an enzyme catalyst, supporting the theory that an RNA world preceded DNA and proteins.