🎓 Meeting Our Concestors
A Walk Back Through Our Ancestry, from Chimpanzees to LUCA and Beyond
by Professor Stephen T. Abedon Steve Abedon, Ph.D., has taught well over 100 individual classes and ~10 individual courses (including introductory biology, microbiology, physiology, biochemistry, etc.) over his 30+ years as a college professor. He has over 150 publications, including multiple monographs, and is ranked in the top 1 or 2 percent among researchers of all disciplines worldwide. His research focuses on bacteriophage biology and phage therapy. (abedon.1@osu.edu)
phage.org | phage-therapy.org | biologyaspoetry.org | abedon.phage.org | google scholar | publications
Jump to: 🚶 The Walk Back | 🦶 The Human Line | 🔎 Concestor Finder | 💡 Innovations | ⏳ Deep Time | 🦴 How We Know | 🧪 Before LUCA | 🧮 More Calculators
The Walk Back takes the 38 rendezvous in order, with the living relatives who join at each, fossils from along the way, and the innovations that arose on our line. The Human Line then zooms in on the last 7 million years, the stretch we know best, thanks to a whole field, paleoanthropology, devoted to it: some two dozen hominin species, when and where they lived, how their brains compared, and which of them may have been our ancestors. Concestor Finder finds the concestor of any two organisms and what each line gained since. Innovations gathers those innovations in one place, and Deep Time squeezes the history of life into a year, a day, or a football field, an idea borrowed from Carl Sagan’s Cosmic Calendar. How We Know explains why fossils are relatives rather than ancestors and where the dates come from, and Before LUCA goes back further than the tree of life itself can take us. To share a particular section or card, use its 🔗 link, which copies a web address that opens the page right there.
To cite this tool: Abedon, S.T. (2026). Meeting Our Concestors. biologyaspoetry.org/laboratories/concestors/. · DOI: 10.5281/zenodo.23290081
biologyaspoetry.org/laboratories/concestors/ · Abedon’s Books · DOI: 10.5281/zenodo.23290081
How can I improve this page? contact: concestors@biologyaspoetry.org
🚶 The Walk Back
Start with yourself and walk backward in time. At each rendezvous, a group of living organisms joins the walk, because we share an ancestor with them, the concestor, at that point. The concestors get older and the groups joining get larger, until at rendezvous 38 we meet the bacteria and LUCA, the last universal common ancestor of all cellular life.
Each rendezvous below opens to show who joins, roughly when, a few fossils from that stretch of time, and the innovations present in that concestor but not in the next one back. Reading the innovations from the bottom up assembles, one piece at a time, the organism doing the walking. The dates are rounded ranges of published estimates, and they grow less certain the further back we go.
In the lists, “evolved more than once” marks innovations that other lineages arrived at separately, and “timing or placement uncertain” marks those whose position on the walk is debated.
0All living humansToday
The walk starts with us. The most recent individual from whom every living person descends may have lived only a few thousand years ago, because family trees merge quickly as they go back (Rohde et al. 2004). The more famous “Mitochondrial Eve” and “Y-chromosomal Adam” are much older, because each traces only a single line of inheritance, mother to mother or father to son. The fossils below come from our side of the split with chimpanzees, a stretch of about 6 to 7 million years; the Human Line tab covers some two dozen species from that stretch in more detail.
- Walking upright on two legs. Bipedal walking is evident in fossils from at least 4.4 million years ago and possibly earlier. (timing or placement uncertain)
- Stone tools. The oldest known stone tools, from Lomekwi, Kenya, are about 3.3 million years old.
- Much larger brains. Brain size roughly tripled over the last 2 to 3 million years.
- Control of fire. Evidence for regular use of fire ranges from about 1 million to a few hundred thousand years ago and is debated. (timing or placement uncertain)
- Spoken language. When language arose is unknown, because speech does not fossilize. (timing or placement uncertain)
- Symbolic art and ornament. Engraved ochre and shell beads appear by about 100,000 years ago.
- Sahelanthropus tchadensis (~7 million years). Possibly on our side of the split with chimpanzees, possibly not; its placement is debated.
- Ardipithecus ramidus (“Ardi”) (4.4 million years). Probably walked upright on the ground while still climbing well.
- Australopithecus afarensis (“Lucy”) (3.2 million years). Upright walker with an ape-sized brain; a relative, and not necessarily an ancestor.
- Homo erectus (~1.9 million to ~100,000 years). The first known human species to spread beyond Africa.
- Neanderthals and Denisovans (~400,000 to ~40,000 years). Our closest extinct cousins; they interbred with our ancestors, so many living people carry some of their DNA.
- Jebel Irhoud fossils (~300,000 years). Among the oldest fossils assigned to our own species.
1Chimpanzees and bonobos6–8 million years ago▶ 1 video
Chimpanzees and bonobos are our closest living relatives. They are exactly as far from this concestor as we are: they did not stop evolving while we changed. The two species split from each other much later, roughly 1 to 2 million years ago.
- Knuckle-walking. Shared with gorillas, but it may have evolved separately in the two. (evolved more than once; timing or placement uncertain)
- Fossil chimpanzee teeth (~500,000 years). Almost no fossils are known from the chimpanzee side of the split; a few teeth from Kenya are the main exception.
The split may not have been clean. Some genetic studies suggest that the two populations continued to exchange genes for a time after they began to diverge.
More about chimpanzees and bonobos on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
2Gorillas8–10 million years ago
Gorillas join next. For a surprising share of our genome, a gorilla is closer to us than a chimpanzee is, because gene lineages do not always split in the same order as species do.
- Danuvius guggenmosi (“Udo”) (~11.6 million years). An ape from Bavaria, Germany, described in 2019 as climbing with its body upright and walking on two legs along branches. That interpretation has been challenged, and where Danuvius belongs among the great apes is uncertain.
- Chororapithecus abyssinicus (~8 million years). Proposed as an early relative of gorillas, a claim that remains debated.
More about gorillas on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
3Orangutans13–17 million years ago▶ 1 video
Orangutans are the only great apes living in Asia today, but the fossil record shows that great apes were once widespread across Europe and Asia.
- Slow life history: long childhoods and long lives. Shared by all great apes and taken further in humans. (timing or placement uncertain)
- Sivapithecus (~12.5 to 8.5 million years). Its face closely resembles an orangutan’s.
- Gigantopithecus blacki (~2 million to ~250,000 years). A giant ape, perhaps twice the weight of a gorilla, known only from about 2,000 teeth and four lower jaws. Proteins from its tooth enamel place it with the orangutans. It probably died out as its forests shrank and fruit became scarce.
More about orangutans on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
4Gibbons17–21 million years ago
Gibbons are the “lesser apes,” and the acrobats of the group. With them we arrive at the concestor of all apes.
- Loss of the tail. Apes lack an external tail; the tailbone is what remains. (a loss)
- Flexible shoulders for hanging below branches. Taken to an extreme by gibbons. (timing or placement uncertain)
- Swinging arm over arm through the trees (brachiation)
- Loud, elaborate songs
- Proconsul (~23 to 17 million years). An early ape or a close relative of apes; it had no tail but otherwise moved much like a monkey.
More about gibbons on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
5Old World monkeys25–33 million years ago
Old World monkeys and apes share downward-pointing, narrow nostrils (“catarrhine” means down-nosed) and, more importantly, three-color vision.
- Routine three-color (trichromatic) vision. Howler monkeys of the Americas evolved the same ability separately. (evolved more than once)
- Aegyptopithecus zeuxis (~30 million years). A small primate from Egypt close to the split between monkeys and apes.
More about old world monkeys on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
6New World monkeys35–45 million years ago
New World monkeys live only in the Americas. The leading explanation for how they got there is that their ancestors rafted across a then-narrower Atlantic from Africa on floating vegetation.
- Eye sockets closed off at the back. A bony wall separates the eye from the chewing muscles in all monkeys and apes.
More about new world monkeys on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
7Tarsiers55–70 million years ago
Tarsiers look like lemurs, but they are closer to us. Like us, they have dry noses, and like us they cannot make their own vitamin C.
- Loss of the ability to make vitamin C. Guinea pigs, some bats, and some birds lost it separately. (a loss; evolved more than once)
- A dry nose, without the moist, dog-like rhinarium (a loss)
- Archicebus achilles (~55 million years). A tiny primate near the tarsier–anthropoid split; its exact placement is debated.
More about tarsiers on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
8Lemurs and lorises65–80 million years ago
This is the concestor of all primates. Molecular clocks put it before the asteroid impact that ended the age of dinosaurs 66 million years ago, while the oldest clear primate fossils are younger.
- Nails instead of claws on most fingers and toes
- Grasping hands and feet with an opposable big toe
- Forward-facing eyes with overlapping fields of view. Cats and owls evolved the same arrangement separately. (evolved more than once)
- A toothcomb of forward-pointing lower teeth, used in grooming
- Darwinius masillae (“Ida”) (~47 million years). Announced in 2009 as a link to our own lineage; most later analyses place it among the relatives of lemurs instead.
- Plesiadapis (~58 to 55 million years). A plesiadapiform, from a group of early primate relatives.
More about lemurs and lorises on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
9Colugos and tree shrews75–90 million years ago
Colugos glide rather than fly, and they are not lemurs. Which of the two groups is closer to primates remains unsettled, so they join here together.
- Gliding membranes (colugos). Flying squirrels and sugar gliders evolved gliding separately. (evolved more than once)
- Purgatorius (~66 to 65 million years). Among the oldest known primate relatives, from just after the asteroid impact.
Whether colugos or tree shrews are the closer relatives of primates is still debated.
More about colugos and tree shrews on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
10Rodents and rabbits80–95 million years ago
Rodents are the largest group of mammals, with over 2,000 species. The laboratory mouse is a relative that joined our pilgrimage surprisingly late, which is part of why it works as a model for human biology.
- Ever-growing gnawing incisors
More about rodents and rabbits on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
11Laurasiatheres85–100 million years ago
A huge, varied group joins here: carnivores, hoofed mammals, bats, and whales. Whales are hoofed mammals that returned to the sea, and their closest living relatives are hippopotamuses.
- Powered flight (bats). Birds and pterosaurs evolved flight separately. (evolved more than once)
- Echolocation (bats and toothed whales). Evolved separately in bats and in toothed whales. (evolved more than once)
- A return to life in the sea (whales)
- Pakicetus (~50 million years). An early, land-dwelling relative of whales.
- Ambulocetus (~49 million years). The “walking whale,” at home both on land and in water.
More about laurasiatheres on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
12Afrotheres and xenarthrans95–110 million years ago
With these two groups we reach the concestor of all placental mammals. Afrotheres arose in Africa and xenarthrans in South America, possibly reflecting the breakup of the old southern supercontinent.
- Long pregnancy supported by an elaborate placenta. Marsupials have a placenta too, but a short-lived one. (timing or placement uncertain)
- A corpus callosum linking the two halves of the brain
- A trunk (elephants)
- Bony armor (armadillos). Many unrelated animals, from turtles to extinct ankylosaurs, evolved armor separately. (evolved more than once)
- Glyptodon (~2 million to ~12,000 years). A car-sized armored relative of armadillos.
- Megatherium (~5 million to ~12,000 years). An elephant-sized ground sloth.
Whether afrotheres, xenarthrans, or both together were the first placentals to branch off is unsettled, so they join here as one rendezvous.
More about afrotheres and xenarthrans on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
13Marsupials150–170 million years ago
Marsupials give birth to tiny young that finish developing while attached to a nipple, often in a pouch. Their split from our line happened in the age of dinosaurs.
- Live birth without eggshells. Many lizards, snakes, and sharks evolved live birth separately. (evolved more than once)
- Nipples (teats)
- External ear flaps (pinnae) (timing or placement uncertain)
- Juramaia sinensis (~160 million years). Proposed as an early relative on our side of this split; its age and placement are debated.
- Sinodelphys szalayi (~125 million years). Proposed as an early relative on the marsupial side, also debated.
More about marsupials on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
14Monotremes170–190 million years ago
The egg-laying mammals complete the mammal family. Many of the features we think of as mammalian arose gradually over the long stretch before this concestor, among the extinct “mammal-like reptiles” (synapsids).
- Hair. Fossils show fur in close relatives of mammals, so hair may be older than this concestor. (timing or placement uncertain)
- Milk and mammary glands
- A lower jaw made of a single bone
- Three middle-ear bones. Fossils suggest that the final arrangement evolved separately in monotremes and in the ancestors of marsupials and placentals. (evolved more than once)
- Warm-bloodedness (endothermy). Birds evolved it separately; when it began on our line is debated. (evolved more than once; timing or placement uncertain)
- Electroreception in the bill (platypus). Sharks evolved electroreception separately. (evolved more than once)
- Venomous spurs (male platypus)
- Thrinaxodon (~250 million years). A cynodont, from the group that includes mammals’ ancestors.
- Morganucodon (~205 million years). A small, shrew-like close relative of mammals.
More about monotremes on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
15Reptiles and birds310–325 million years ago▶ 1 video
Birds are dinosaurs, and crocodiles are closer to birds than to lizards. Our side of this split is the synapsids, which include the sail-backed Dimetrodon, a relative of ours and not a dinosaur.
- The amniotic egg. Membranes enclosing the embryo in its own pond freed reproduction from water.
- Tough, waterproof skin
- Breathing by expanding the rib cage (timing or placement uncertain)
- Feathers and flight (birds). Bats and pterosaurs evolved flight separately. (evolved more than once)
- Shells (turtles)
- Hylonomus (~312 million years). One of the earliest known reptiles, found inside fossil tree stumps in Nova Scotia.
- Dimetrodon (~295 million years). A synapsid on our side of the split.
- Archaeopteryx (~150 million years). A feathered dinosaur close to the origin of birds.
More about reptiles and birds on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
16Amphibians335–360 million years ago▶ 1 video
With amphibians we reach the concestor of all four-limbed vertebrates. The move onto land happened over tens of millions of years, and some of the best-known fossils are side branches of that story.
- Limbs with fingers and toes. Early limbs had more than five digits; Acanthostega had eight fingers.
- A neck, letting the head turn independently of the body
- Breathing through the skin
- Metamorphosis from tadpole to adult (frogs)
- Tiktaalik roseae (~375 million years). A fish with a neck and sturdy fins, found by Neil Shubin’s team. Four-limbed trackways from Poland are older still, so Tiktaalik is best seen as a late-surviving relative, not an ancestor.
- Acanthostega gunnari (~365 million years). Had limbs with digits but was still mostly aquatic.
- Ichthyostega (~365 million years). Found in Greenland in the 1930s; strong forelimbs, seven toes on each hind foot, and a paddle-like tail. It probably moved on land by hauling itself along with its front limbs, and it spent much of its time in water.
More about amphibians on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
17Lungfish390–420 million years ago
Lungfish, not coelacanths, are the closest living fish relatives of four-limbed animals. That means a lungfish is more closely related to you than it is to a salmon.
- Eusthenopteron foordi (~385 million years). A lobe-finned fish whose fin bones match those of our arms.
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18Coelacanths410–425 million years ago
Coelacanths were known only as fossils until a living one was caught off South Africa in 1938. They are often called “living fossils,” but living coelacanths are not the same species as the fossil ones, and they have been evolving all along.
- Fleshy, lobed fins with a single bone at the base. That single bone corresponds to our upper arm and thigh bones.
- Guiyu oneiros (~423 million years). An early bony fish with a mix of features, close to the lobe-finned lineage.
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19Ray-finned fishes420–440 million years ago
Ray-finned fishes make up about half of all vertebrate species. This concestor had lungs; most ray-finned fish later turned them into swim bladders, rather than the other way around.
- Bone replacing cartilage in the internal skeleton
- Lungs. Air-breathing sacs, later swim bladders in most ray-finned fish.
- A gas-filled swim bladder for buoyancy
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20Sharks and rays440–470 million years ago
Here we meet the concestor of all jawed vertebrates. Jaws evolved from the supports of the front gill arches, and the adaptive immune system that lets us make antibodies also appears on our line here.
- Jaws. Derived from gill-arch supports.
- Paired pelvic fins (the forerunners of legs)
- Adaptive immunity with antibodies and T cells. Lampreys and hagfish evolved a different adaptive immune system separately. (evolved more than once)
- Electroreception (sharks and rays). The platypus evolved electroreception separately. (evolved more than once)
- Entelognathus primordialis (~423 million years). A placoderm (armored fish) with jaw bones like those of bony fishes.
- Dunkleosteus (~370 million years). A giant placoderm, from an extinct group close to the origin of jaws.
More about sharks and rays on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
21Lampreys and hagfish500–600 million years ago
The jawless lampreys and hagfish complete the vertebrates. Their concestor with us already had a skull, camera-type eyes, and neural crest cells, a cell type that builds much of the vertebrate head.
- A skull (cranium)
- Neural crest cells. Embryonic cells that build much of the face, the jaws, and the peripheral nerves.
- Camera-type eyes. Octopuses and squid evolved camera-type eyes separately. (evolved more than once)
- Whole-genome duplications. At least one doubling of the entire genome happened on this stretch; how many, and when, is debated. (timing or placement uncertain)
- A separate adaptive immune system (variable lymphocyte receptors) (evolved more than once)
- Defensive slime (hagfish)
- Haikouichthys and Myllokunmingia (~518 million years). Early jawless vertebrates from the Chengjiang fossil beds of China.
- Conodonts (~500 to ~200 million years). Eel-like animals known mostly from tiny tooth-like elements.
More about lampreys and hagfish on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
22Tunicates (sea squirts)520–650 million years ago
Tunicates are the sister group of vertebrates, our closest invertebrate relatives, and that came as a surprise. An adult sea squirt is a filter-feeding bag attached to a rock, with no notochord, no nerve cord along its back, and no tail; only its short-lived swimming larva has those chordate features. Lancelets, by contrast, keep all of them as adults and look far more like a small fish, so for most of the twentieth century they were taken to be our closest invertebrate relatives, with tunicates as the earliest chordate branch. Comparisons of more than a hundred genes reversed that order (Delsuc et al. 2006), and larger studies since have agreed.
How can a bag attached to a rock be closer to us than a fish-shaped lancelet? Tunicates have simply changed more since the split: most lost the chordate body plan as adults and evolved a fast-changing, streamlined genome. Larvaceans (appendicularians) are an exception, keeping the tadpole-like body throughout life. Lancelets look like a stage on the way to vertebrates because they have changed less, not because they are more closely related. Resemblance and relatedness are different things.
- Forerunners of neural crest and placode cells. Tunicate embryos have cells resembling both, the vertebrate cell types that build much of the head and its sense organs. (timing or placement uncertain)
- A tunic made of cellulose. Tunicates are the only animals known to make cellulose, using genes apparently acquired from bacteria by horizontal gene transfer.
More about tunicates (sea squirts) on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
23Lancelets530–650 million years ago
Lancelets are small, fish-shaped filter feeders, and with them we reach the concestor of all chordates. They are the sister group of tunicates and vertebrates together, so a lancelet is exactly as closely related to a sea squirt as it is to us. Its body, with a notochord, a nerve cord along the back, gill slits, and blocks of muscle along a tail, probably resembles the chordate concestor more closely than either tunicates or vertebrates do. The same body plan is still visible in every human embryo.
- A notochord. A flexible supporting rod, replaced by the backbone in most vertebrates.
- A hollow nerve cord along the back
- A tail extending past the anus
- An endostyle, the forerunner of the thyroid gland
- Pikaia gracilens (~508 million years). From the Burgess Shale; an early chordate or close relative.
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24Echinoderms and acorn worms540–660 million years ago
A sea star is closer to us than it is to an octopus. Sea stars are bilaterally symmetrical as larvae and take on their five-part symmetry only as adults.
- Pharyngeal (gill) slits. Openings in the throat, present in human embryos; they may be older than this concestor. (timing or placement uncertain)
More about echinoderms and acorn worms on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
25Protostomes555–680 million years ago
Most animal species join here at once. Molecular clocks place this concestor before the Cambrian explosion of animal fossils about 539 million years ago, a gap that suggests earlier animals were small, soft, or both.
- A through-gut with a separate mouth and anus (timing or placement uncertain)
- Excretory organs (nephridia) (timing or placement uncertain)
- A jointed exoskeleton that is molted (arthropods)
- Camera-type eyes (octopus and squid). Vertebrates evolved camera-type eyes separately. (evolved more than once)
- Kimberella (~555 million years). A slug-like animal, possibly a relative of molluscs.
- Trilobites (~521 to 252 million years). Arthropods, and among the most familiar fossils.
- Saccorhytus coronarius (~535 million years). Announced in 2017 as the earliest known deuterostome, a relative on our side of this split; reexamined in 2022 as an early protostome instead (Liu et al. 2022).
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26Acoel flatworms570–700 million years ago▶ 1 video
These small, simple worms have a mouth but no anus. If they branched off before all other bilaterians, as many analyses suggest, their concestor with us was the first bilaterian.
- Bilateral symmetry with a front and a back end. Some cnidarians have a degree of bilateral symmetry too. (timing or placement uncertain)
- A third tissue layer (mesoderm). The embryonic source of muscles, blood, and bone.
- Nerves concentrated at the front end (timing or placement uncertain)
- Ikaria wariootia (~555 million years). A rice-grain-sized animal proposed as an early bilaterian, based on its shape and the burrows it may have made.
Where these worms belong is debated. Some analyses place them with the deuterostomes instead, which would remove this rendezvous from our path.
More about acoel flatworms on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
27Cnidarians600–750 million years ago
Cnidarians have nerve nets and muscles but no brain. Their stinging cells, among the most complex structures made by any single cell, are their own invention.
- Neurons and synapses. Comb jellies have neurons too, but whether they evolved separately there is debated. (evolved more than once; timing or placement uncertain)
- Hox and ParaHox body-patterning genes (timing or placement uncertain)
- Stinging cells (cnidocytes)
- Alternation between polyp and medusa stages
- Dickinsonia (~558 million years). An Ediacaran organism shown to be an animal by traces of cholesterol preserved with it; where it fits among animals is unclear.
- Haootia quadriformis (~560 million years). A possible early cnidarian with preserved muscle fibers.
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28Placozoans600–800 million years ago
Placozoans are flat, crawling animals only a few cells thick, with no neurons, muscles, or gut. Whether they are simple from the start or simplified from something more complex is not known.
- An extremely simple body with only a handful of cell types
Placozoans may be closer to cnidarians than to us, in which case they would join at the cnidarian rendezvous.
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29Sponges650–850 million years ago
Sponges have no neurons or muscles. They pump water through a system of canals, trapping food with collared cells much like choanoflagellates.
- Distinctive fusions of ancestral chromosomes. Shared by sponges and all animals closer to us, and a key line of evidence that comb jellies branched off first (Schultz et al. 2023). (timing or placement uncertain)
- A canal system lined with collared cells (choanocytes)
- Skeletons of glassy or chalky spicules
- Sponge biomarkers (possibly over 635 million years). Chemical traces of sponge-like sterols in ancient rocks; whether sponges made them is debated.
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30Comb jellies650–900 million years ago
Comb jellies swim with rows of fused cilia that scatter light into rainbows. Whether they or sponges were the first to branch off from the rest of the animals has been argued for more than a decade; recent evidence favors comb jellies.
- Multicellularity with many specialized cell types. Plants, fungi, and red and brown algae became complexly multicellular separately. (evolved more than once)
- Eggs and sperm, and embryos that develop from a hollow ball of cells (timing or placement uncertain)
- Collagen scaffolding between cells
If sponges instead branched off first, sponges and comb jellies would trade places on this walk.
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31Choanoflagellates700 million to 1 billion years ago
Choanoflagellates are the closest living relatives of animals. Some form rosette-shaped colonies, and in one species colony formation is triggered by a molecule made by bacteria.
- A collar of microvilli around a single flagellum. Resembles the collared cells of sponges; whether the two are truly equivalent is debated. (timing or placement uncertain)
- Cadherin adhesion proteins and tyrosine-kinase signaling. Molecules that animals later used to glue cells together and coordinate them.
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32Filastereans and ichthyosporeans800 million to 1.1 billion years ago
These little-known single-celled organisms carry many genes once thought to be unique to animals.
- Integrin adhesion proteins. Present before animals existed, then used by animals to attach cells to their surroundings. (timing or placement uncertain)
- Cells that aggregate into temporary multicellular clumps (Capsaspora)
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33Fungi900 million to 1.5 billion years ago
Fungi are closer to us than to plants. The name of this group, opisthokonts (“rear pole”), refers to the single flagellum that pushes swimming cells from behind, as in a chytrid zoospore or a human sperm cell.
- Hyphae and external digestion
- Cell walls of chitin. Insects and crustaceans also make chitin, for their exoskeletons.
- Ourasphaira giraldae (~0.9 to 1 billion years). Proposed as the oldest known fungus; the identification is debated.
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34Amoebozoans1–1.6 billion years ago
Cellular slime molds spend most of their lives as single amoebas, then stream together by the tens of thousands to form a crawling slug and a stalked fruiting body.
- Aggregating into a multicellular slug (cellular slime molds). One of several separate origins of multicellularity. (evolved more than once)
This rendezvous exists as a separate stop only if the root of the eukaryote tree lies outside the group that includes animals, fungi, and amoebozoans, which is the most common view but is not settled.
More about amoebozoans on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
35Plants, algae, and all other eukaryotes1.2–1.9 billion years ago
This is LECA, the last eukaryotic common ancestor. LECA already had a nucleus, mitochondria, and meiotic sex, so the transformation from a simpler cell happened before it, along a stretch that left no living side branches. The mitochondria came from a captured alphaproteobacterium, which gives us a second line of ancestry, through bacteria.
- A nucleus
- Mitochondria, from an engulfed alphaproteobacterium
- Mitosis, meiosis, and sex
- Internal membranes: endoplasmic reticulum and Golgi apparatus
- The eukaryotic flagellum (cilium), with its 9 + 2 arrangement
- Genes interrupted by introns and spliced by the spliceosome
- Chloroplasts, from an engulfed cyanobacterium (plants and algae). Later passed on to other eukaryotes by further engulfments.
- Cellulose cell walls (plants)
- Qingshania magnifica (~1.63 billion years). Reported in 2024 as a multicellular eukaryote, among the oldest known.
- Bangiomorpha pubescens (~1.05 billion years). A red alga, and the oldest fossil that can be placed in a living group of eukaryotes with some confidence.
Where the root of the eukaryote tree lies is not settled, so which eukaryotes join here and which join at the amoebozoan rendezvous could change.
More about plants, algae, and all other eukaryotes on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
36Asgard archaea1.8–3 billion years ago
Eukaryotes appear to have arisen from within the Asgard archaea, which carry many genes once thought to be unique to eukaryotes (Eme et al. 2023). If so, our host-cell ancestry is archaeal, and the familiar three domains of life become two: Bacteria and Archaea, with eukaryotes as a branch of the archaea.
- “Eukaryotic signature proteins” for shaping membranes and the cytoskeleton. Including relatives of actin and of the proteins that bend membranes. (timing or placement uncertain)
- Long, thin cell extensions (Prometheoarchaeum)
Which Asgard group is closest to eukaryotes is still being worked out.
More about asgard archaea on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
37Other archaea3–4 billion years ago
Archaea look like bacteria under the microscope but differ in their membranes and in much of their molecular machinery. Oddly, eukaryotes have bacteria-type membrane lipids despite their archaeal ancestry, a puzzle called the lipid divide.
- Histone proteins that package DNA. Found in many archaea and in all eukaryotes. (timing or placement uncertain)
More about other archaea on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
38Bacteria3.5–4.33 billion years ago
With the bacteria we reach LUCA, the last universal common ancestor of all cellular life. One recent estimate puts LUCA at about 4.2 billion years ago and reconstructs it as a fairly complex cell with around 2,600 proteins and elements of an antiviral immune system (Moody et al. 2024), which suggests that LUCA was already contending with viruses. Bacteria also bring their own viruses, the bacteriophages.
- The genetic code
- Ribosomes and protein synthesis
- ATP synthase driven by ion gradients across a membrane
- A DNA genome. Bacteria and archaea copy DNA with largely unrelated enzymes, so whether LUCA had a DNA genome is debated. (timing or placement uncertain)
- A cell membrane. Bacterial and archaeal membranes are built differently, so the nature of LUCA’s membrane is debated. (timing or placement uncertain)
- Oxygen-producing photosynthesis (cyanobacteria). The source of the oxygen that began building up about 2.4 billion years ago.
- Peptidoglycan cell walls
- Stromatolites (~3.48 billion years and younger). Layered mounds built by microbial mats; the oldest examples are widely, though not universally, accepted as biological.
- Carbon isotope signatures (~3.7 to 4.1 billion years). Carbon enriched in the light isotope favored by living things; claims this old are contested.
More about bacteria on Wikipedia | Compare in the Concestor Finder | ↑ Back to the timeline
🧭 What Is on Each Tab
🧪 Related Laboratories
🦶 The Human Line
On our side of the split with chimpanzees, the last 6 to 7 million years, we can do far better than a single rendezvous. Paleoanthropology, the study of human origins, has recovered thousands of fossils from this stretch, along with stone tools, footprints, and, for the most recent, DNA and proteins. The 26 entries below are hominins: species on our side of that split. Most of them were not our ancestors, and several other human species were still alive when our own species appeared.
Each entry is marked as possibly on our line, a side branch, or placement debated. “Possibly on our line” means a candidate ancestor, in about the right place at about the right time, not a species shown to be one.
Homo sapiens (us)about 300,000 years ago to todayus▶ 1
Our species appears in Africa by about 300,000 years ago. Groups of Homo sapiens reached the Middle East by roughly 180,000 years ago, but the dispersal that populated the rest of the world began about 60,000 to 50,000 years ago. Footprints at White Sands, New Mexico, suggest people were in the Americas by about 21,000 to 23,000 years ago. How far back our own lineage goes is debated. Genetic estimates put our split from the ancestors of Neanderthals and Denisovans at roughly 550,000 to 750,000 years ago, with those two as each other’s closest relatives. A 2025 study of the reconstructed Yunxian 2 skull from China, about a million years old, instead grouped it with the Denisovans as our closest relatives and placed the split from them more than a million years ago, with Neanderthals branching off earlier still (Feng et al. 2025); that conclusion remains controversial.
Denisovans (known first from DNA)about 300,000 to 30,000 years agoside branch▶ 2
Denisovans were discovered in 2010 from the DNA of a finger bone in Denisova Cave, Siberia, before anyone knew what they looked like. In 2025, proteins and mitochondrial DNA identified a nearly complete skull from Harbin, China, at least 146,000 years old, as Denisovan (Fu et al. 2025). That skull had been named Homo longi, which may become the Denisovans’ formal name. Some people in Papua New Guinea and Australia carry roughly 3 to 5 percent Denisovan DNA, and smaller amounts are widespread in Asia. In 2026, Bianfu Cave in Yunnan, southwestern China, gave the fullest picture yet of how Denisovans lived: skull fragments, teeth, and the first known Denisovan arm bone, identified by their proteins, together with more than 1,300 simple stone tools and over 60,000 animal bones from an occupation lasting from roughly 190,000 to 70,000 years ago. The bones show that they hunted large animals such as water buffalo and deer, and mostly adults in their prime. The video on the Homo sapiens entry covers the Harbin skull and the debate over how Denisovans are related to us.
Homo neanderthalensis (Neanderthals)about 430,000 to 40,000 years agoside branch▶ 1
Neanderthals were stocky, cold-adapted hunters with brains as large as ours or larger. They made sophisticated stone tools, controlled fire, and buried at least some of their dead. They interbred with our ancestors, so most people whose ancestry lies outside Africa carry about 1 to 2 percent Neanderthal DNA. Pierced marine shells, some still holding red pigment, from Cueva de los Aviones in Spain, about 115,000 years old, suggest they adorned themselves long before modern humans reached Europe. They disappear from most of Europe by about 40,000 years ago, possibly lingering in southern Iberia until about 37,000 years ago.
Homo luzonensisabout 67,000 to 50,000 years agoside branch
Described in 2019 from teeth and hand and foot bones, Homo luzonensis combined small teeth with curved finger and toe bones reminiscent of australopiths. Like Homo floresiensis, it lived on an island that could be reached only by crossing water; stone tools show that hominins were on Luzon 700,000 years ago. The video on the Homo erectus entry discusses how early hominins might have reached such islands.
Homo floresiensis (“the hobbit”)about 100,000 to 60,000 years agoside branch
About a meter tall with a brain the size of a chimpanzee’s, yet making stone tools, Homo floresiensis lived on Flores until about 60,000 years ago, overlapping with our own species. Similar small hominins lived on the island 700,000 years ago, so the lineage was there a long time, possibly shrinking in body size, as island animals often do. The video on the Homo erectus entry discusses whether it descends from erectus.
Homo nalediabout 335,000 to 236,000 years agoside branch▶ 1
Found from 2013 onward deep in the Rising Star cave system by a team led by Lee Berger, Homo naledi had a small brain but lived as recently as about 250,000 years ago, when our own species was already appearing. Claims that it buried its dead and engraved cave walls are contested.
Homo heidelbergensisabout 700,000 to 200,000 years agoplacement debated
A large-brained species, or perhaps a grab bag of several, often proposed as the last common ancestor of Neanderthals, Denisovans, and us. How many species these fossils represent, and which name should apply to them, is much debated, a problem nicknamed the “muddle in the middle.” The video on the Homo sapiens entry covers a 2025 attempt to resolve it using the Yunxian skull from China. The video on the Homo erectus entry discusses the problem.
Homo antecessorabout 900,000 to 800,000 years agoplacement debated▶ 1
For decades the oldest humans known from western Europe, until the 2025 description of Pink, an older face from nearby Sima del Elefante that its discoverers consider a different and more primitive kind of human (see Homo erectus). Proteins recovered from an 800,000-year-old tooth place Homo antecessor close to, but not necessarily on, the line leading to Neanderthals, Denisovans, and us. Cut marks on its bones are among the oldest evidence of cannibalism.
Homo erectus (including African Homo ergaster)about 2 million years ago to 110,000 years agopossibly on our line▶ 1
The first hominin with modern body proportions: long legs, short arms, and a body built for walking and perhaps running long distances. Homo erectus left Africa soon after it appeared, reaching Georgia by 1.8 million years ago, and survived in Java until roughly 110,000 years ago; a few researchers have proposed that those last Javan fossils, from Ngandong, were Denisovans instead. The earlier African fossils, often called Homo ergaster, are the best candidates for our ancestors. A freshwater mussel shell from Trinil, Java, 500,000 to 430,000 years old, bears a zigzag line engraved by an erectus, the oldest known abstract marking.
Homo rudolfensisabout 2.4 million to 1.8 million years agoplacement debated
Larger-brained and flatter-faced than Homo habilis, and living at the same time. Whether it is a separate species, and whether either it or habilis is our ancestor, is unsettled.
Homo habilis (“handy man”)about 2.4 million to 1.4 million years agopossibly on our line
Named in 1964 by Louis Leakey and colleagues for its association with stone tools, Homo habilis has a modestly larger brain than australopiths. Stone tools are now known to be older than habilis, and a 2.8-million-year-old jaw from Ledi-Geraru, Ethiopia, is the oldest fossil assigned to Homo.
Australopithecus sedibaabout 2 million years agoplacement debated
Two partial skeletons found in 2008 (the first by Lee Berger’s nine-year-old son) show a mosaic of Australopithecus and Homo features. Proposed as an ancestor of Homo, it is younger than the oldest Homo fossils, so most researchers see it as a late relative instead.
Paranthropus robustusabout 2 million to 1 million years agoside branch
The southern African “robust” australopith, with huge molars and chewing muscles. It lived alongside early Homo, and some of its bones show signs of being eaten by leopards. Its carbon isotopes point to a more mixed diet than that of P. boisei, varying with the seasons. The video on the Paranthropus boisei entry covers this species too.
Paranthropus boisei (“Nutcracker Man”)about 2.3 million to 1.3 million years agoside branch▶ 1
The most extreme of the robust australopiths, with molars several times the area of ours. Despite the nickname, chemical traces in its teeth suggest a diet heavy in grasses and sedges rather than nuts. It survived for about a million years alongside Homo.
Paranthropus aethiopicusabout 2.7 million to 2.3 million years agoside branch
The earliest robust australopith, with a massive crest on top of the skull for anchoring chewing muscles. The video on the Paranthropus boisei entry covers this species too.
Australopithecus garhiabout 2.5 million years agoplacement debated
Found near antelope bones with cut marks from stone tools, Australopithecus garhi has been proposed as a link between A. afarensis and early Homo. The evidence is limited to a few fossils.
Australopithecus africanusabout 3.3 million to 2.1 million years agoplacement debated
The first australopith ever described, by Raymond Dart in 1925, from the skull of a child. Its claim that human ancestry lay in Africa, with upright walking coming before large brains, was widely rejected for decades. Marks inside the child’s eye sockets resemble those left by eagles on the skulls of monkeys they kill today, suggesting that the Taung Child was taken by a large bird of prey.
Kenyanthropus platyopsabout 3.5 million to 3.3 million years agoplacement debated
Australopithecus deyiremedaabout 3.5 million to 3.3 million years agoplacement debated
Named in 2015 from jaws found at Woranso-Mille, in the same region and at the same time as Lucy’s species. In 2025, newly found jaws and teeth allowed its discoverers to assign to it the Burtele foot, a 3.4-million-year-old partial foot found in 2009, whose big toe could still grasp, more like Ardi’s than Lucy’s (Haile-Selassie et al. 2025). Isotopes in its teeth point to a diet of leaves, fruit, and nuts from trees and shrubs, narrower than that of A. afarensis. If the assignment holds, two different kinds of upright walker lived side by side. Some researchers still regard the jaws as falling within the range of A. afarensis.
Australopithecus bahrelghazali (“Abel”)about 3.5 million years agoplacement debated
The only australopith known from central Africa, found in 1995 by a team led by Michel Brunet, some 2,500 kilometers west of the Rift Valley where most early hominins have been found. It showed that australopiths ranged far more widely than the fossil record had suggested. It is known only from jaw fragments and a tooth, and many researchers regard it as a western population of A. afarensis. Carbon isotopes in its teeth point to a diet dominated by grasses and sedges or their underground parts.
Australopithecus afarensis (“Lucy” and her kin)about 3.9 million to 2.9 million years agopossibly on our line▶ 1
Among the best-known early hominins, from hundreds of specimens. Australopithecus afarensis walked upright with an ape-sized brain, and its footprints, preserved in volcanic ash at Laetoli, Tanzania, 3.66 million years ago, look much like ours.
Australopithecus anamensisabout 4.2 million to 3.8 million years agopossibly on our line
Ardipithecus ramidus (“Ardi”)about 4.5 million to 4.3 million years agoplacement debated
Ardi combined a grasping big toe, good for climbing, with a pelvis and foot suited to upright walking on the ground. The skeleton showed that early hominins did not pass through a knuckle-walking stage like that of chimpanzees, a finding that remains debated. The video on the chimpanzee rendezvous looks at what Ardi’s hands suggest about knuckle-walking. The video on the Sahelanthropus entry covers this species too.
Ardipithecus kadabbaabout 5.8 million to 5.2 million years agoplacement debated
Known from teeth, jaw fragments, and a toe bone whose shape suggests upright walking. The video on the Sahelanthropus entry covers this species too.
Orrorin tugenensisabout 6.1 million to 5.7 million years agoplacement debated
Thigh bones suggest that Orrorin walked upright about 6 million years ago, close to the time of our split from chimpanzees. Its curved finger bones suggest it also climbed. The video on the Sahelanthropus entry covers this species too.
Sahelanthropus tchadensis (“Touïmaï”)about 7.2 million to 6.8 million years agoplacement debated▶ 1
The oldest proposed hominin, found far west of the East African Rift where most early hominins come from. Its case rests mainly on a crushed skull, reconstructed by computer: the opening at the base of the skull, where the spinal cord exits, sits farther forward than in chimpanzees, as expected in an upright walker, and its canines are small. A 2022 study of a thigh bone and two forearm bones from the same site argued for habitual upright walking combined with climbing (Daver et al. 2022); other researchers doubt that the bones show upright walking, or that they belong to Sahelanthropus at all.
🌳 A Bush, Not a Ladder
The familiar picture of an ape rising step by step into an upright human is misleading. For most of the last 4 million years, several hominin species lived at the same time, sometimes in the same places: robust Paranthropus alongside early Homo in eastern and southern Africa, for example, and, as recently as about 50,000 years ago, our own species alongside Neanderthals, Denisovans, and the small-bodied humans of Flores and Luzon. Upright walking came first, by millions of years; large brains came late, and small-brained species such as Homo naledi and Homo floresiensis persisted into the time of large-brained ones.
🌍 Leaving Africa
Hominins left Africa more than once. Homo erectus reached Georgia by 1.8 million years ago and East Asia soon after. Our own species reached the Middle East by roughly 180,000 years ago, but the dispersal that gave rise to most people living outside Africa today began about 60,000 to 50,000 years ago. Everyone alive today descends mostly from African populations of Homo sapiens.
🤝 Meeting the Cousins
Ancient DNA, pioneered by Svante Pääbo and colleagues, showed that our ancestors interbred with Neanderthals and Denisovans. Most people with ancestry outside Africa carry about 1 to 2 percent Neanderthal DNA, and some populations in Oceania carry several percent Denisovan DNA as well. Some of these inherited variants still matter: a version of the EPAS1 gene that helps Tibetans live at high altitude appears to have come from Denisovans.
🧠 Why Are We So Different?
Humans are not “more evolved” than other animals. Every lineage alive today has been evolving for the same 4 billion years or so, and an earthworm is as well adapted to soil as we are to our own ways of life. The real question is why our lineage took such an unusual path, toward large brains, language, and accumulated culture, rather than toward claws, venom, armor, or speed.
Freed hands. Charles Darwin suggested in The Descent of Man (1871) that walking upright freed the hands for making and using tools. Hands alone are not the whole story, though: chimpanzees make and use tools too, shaping twigs to fish for termites, as Jane Goodall first reported in 1960, and cracking nuts with stone hammers. What upright walking gave our ancestors was hands that were free while traveling, so that things could be carried. Gordon Hewes proposed in 1961 that carrying food was what made upright walking worthwhile, and wild chimpanzees do walk on two legs more often when carrying scarce, valuable foods (Carvalho et al. 2012). One hypothesis, favored by this page’s author, follows the chain further: free hands, then more capable hands, with a long, strong thumb able to grip firmly against the fingertips, made it possible to keep and carry tools rather than make them, use them, and drop them. A tool that is kept can be reused, improved, taken to new places, and passed to others, and so artifacts, and the know-how to make them, can accumulate. Early toolmakers did carry stone: at Kanjera South, Kenya, about 2 million years ago, some of it came from more than 10 kilometers away. If this chain is right, it unfolded slowly, since upright walking appears more than a million years, and perhaps several million, before the oldest known stone tools, 3.3 million years ago.
Keeping track of what we carry. A second hypothesis of this page’s author follows from the first. Once things could be carried and kept, they could also be lost, and keeping them meant not leaving them behind: the “where are my car keys?” problem. Chimpanzees already have part of the memory this takes. In the Taï forest of Côte d’Ivoire, Christophe Boesch and Hedwige Boesch found that chimpanzees seem to remember where stone hammers lie and usually pick the one closest to the nut tree they are heading for (Boesch & Boesch 1984). A stone left at a nut tree stays put, though. Possessions that travel with their owner are somewhere new each time they are set down, so keeping track of them means updating memory continually and remembering, at every departure, to take everything along. Young children are notoriously bad at this, and many of us find it slipping as we age, which suggests it is not easy. If it takes real mental effort, then carrying added one more demand on the growing brain, alongside the social, technical, and linguistic ones more often proposed. It is offered not as an alternative to those, since human intelligence comes in many forms, but as one more thing our ancestors had to get good at. It sits alongside a broader proposal by Frederick Coolidge and Thomas Wynn (2005) that an expanded working memory, the capacity to hold several things in mind and work with them at once, was central to the evolution of modern human thinking.
Paying for a big brain. The human brain is about 2 percent of body weight but uses roughly 20 percent of the energy a resting body burns. Leslie Aiello and Peter Wheeler proposed in 1995 that our ancestors paid for larger brains with smaller guts, which a richer diet made possible. Richard Wrangham has argued that cooking was the key, since it unlocks far more energy from food. The difficulty is timing: brains began enlarging about 2 million years ago, while widely accepted evidence for controlled fire is about a million years younger, so whether cooking drove brain growth or followed it is debated.
Culture that accumulates. Each human generation inherits what earlier ones learned and adds to it, so that no one needs to invent fire, spears, or boats from scratch. Joseph Henrich and others argue that this cumulative culture, more than individual intelligence, explains our success, and that it depends on large, well-connected populations through which knowledge can spread and survive. Carrying belongs to the same story: a portable tool can travel between people and between groups, taking its makers’ know-how with it. The same advantage has been suggested for modern humans over the last Neanderthals (see the video on the Neanderthal entry). Equipped with tools and cooperating in groups, our species has become what Boris Worm and Robert Paine called a “hyperkeystone species,” one that shapes ecosystems everywhere it lives.
Still evolving. Culture did not take us out of biological evolution; it changed what evolution acts on. The ability of adults to digest milk spread among herding peoples within roughly the last 10,000 years, and a Denisovan version of a gene now helps Tibetans live at high altitude. Our biology and our culture have been shaping each other all along.
Why only us? Why ours is the only human species left is still an open question. Larger and better-connected populations, interbreeding that absorbed other groups into ours, climate swings that hit small populations hardest, and plain luck have all been proposed, and the answer may well involve several of these at once.
This section was prompted by an answer on Quora by WildCanopy.
- Aiello, L.C., & Wheeler, P. (1995). The expensive-tissue hypothesis: The brain and the digestive system in human and primate evolution. Current Anthropology, 36, 199–221. doi:10.1086/204350
- Boesch, C., & Boesch, H. (1984). Mental map in wild chimpanzees: An analysis of hammer transports for nut cracking. Primates, 25, 160–170. doi:10.1007/BF02382388
- Carvalho, S., Biro, D., Cunha, E., Hockings, K., McGrew, W.C., Richmond, B.G., & Matsuzawa, T. (2012). Chimpanzee carrying behaviour and the origins of human bipedality. Current Biology, 22, R180–R181. doi:10.1016/j.cub.2012.01.052
- Coolidge, F.L., & Wynn, T. (2005). Working memory, its executive functions, and the emergence of modern thinking. Cambridge Archaeological Journal, 15, 5–26. doi:10.1017/S0959774305000016
- Darwin, C. (1871). The Descent of Man, and Selection in Relation to Sex. London: John Murray.
- Hewes, G.W. (1961). Food transport and the origin of hominid bipedalism. American Anthropologist, 63, 687–710. doi:10.1525/aa.1961.63.4.02a00020
- Henrich, J. (2016). The Secret of Our Success: How Culture Is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter. Princeton: Princeton University Press.
- Worm, B., & Paine, R.T. (2016). Humans as a hyperkeystone species. Trends in Ecology & Evolution, 31, 600–607. doi:10.1016/j.tree.2016.05.008
- Wrangham, R. (2009). Catching Fire: How Cooking Made Us Human. New York: Basic Books.
📏 Milestones on Our Side of the Split
| When | What |
|---|---|
| at least 4.4 million years ago, possibly ~6 | Upright walking evident in fossils |
| 3.66 million years ago | Laetoli footprints |
| about 3.4 million years ago, contested | Marks on animal bones at Dikika, Ethiopia, interpreted as butchery with stone tools; others attribute them to trampling |
| 3.3 million years ago | Oldest known stone tools (Lomekwi, Kenya) |
| 2.8 million years ago | Oldest fossil assigned to Homo (Ledi-Geraru jaw) |
| about 2.6 million years ago, possibly earlier | Oldowan stone tools |
| about 1.95 million years ago, contested | Cut-marked animal bones at Grăunceanu, Romania, the oldest proposed evidence of hominins in Europe |
| about 1.8 million years ago | Hominins outside Africa (Dmanisi, Georgia) |
| about 1.76 million years ago | Acheulean hand axes |
| about 1.4 to 1.1 million years ago | Hominins in western Europe: stone tools at Orce, Spain, and Korolevo, Ukraine, and Pink, the oldest face from the region (Atapuerca, Spain) |
| about 1 million years ago, debated | Regular use of fire |
| about 950,000 to 850,000 years ago | Footprints at Happisburgh, England, the earliest evidence of hominins so far north |
| about 550,000 to 750,000 years ago | Our lineage splits from that of Neanderthals and Denisovans (genetic estimates; one 2025 fossil analysis argues for more than a million years ago) |
| about 300,000 years ago | Oldest fossils of Homo sapiens |
| about 150,000 to 200,000 years ago | Mitochondrial Eve |
| at least 100,000 years ago | Oldest widely accepted intentional burials |
| about 60,000 to 50,000 years ago | Main dispersal of Homo sapiens out of Africa; interbreeding with Neanderthals |
| more than 45,000 years ago | Oldest known figurative cave paintings (Sulawesi, Indonesia) |
| about 40,000 years ago | Last Neanderthals |
| about 21,000 to 23,000 years ago | People in the Americas (White Sands footprints) |
| about 12,000 years ago | Farming begins |
🔎 Concestor Finder
Pick any two organisms to find their concestor, when it lived, and what each line gained after the two parted ways. The organisms are grouped by the rendezvous at which they join our walk.
The walk follows only our own line, so for two organisms that join at the same rendezvous (a dog and a cat, for example), the finder can say only that their concestor is younger than that rendezvous. The innovations listed for other groups are a small sample of each group’s own history.
💡 Innovations
These are the 75 innovations that arose on our own line, placed between the two rendezvous that bracket them, together with 54 innovations of the groups that joined us along the way. An innovation listed at a rendezvous was present in that concestor, so it arose sometime between that concestor and the next one back. Losses count as innovations too: losing a tail or the ability to make vitamin C changed our ancestors as surely as gaining a jaw.
| Innovation | Kind | When it arose | On the calendar | Where on the walk |
|---|---|---|---|---|
| Walking upright on two legs (timing or placement uncertain) | Body plan | about 5.5 million years ago | Our line, since the split with chimpanzees | |
| Stone tools The oldest known stone tools, from Lomekwi, Kenya, are about 3.3 million years old. | Behavior and culture | about 3.3 million years ago | Our line, since the split with chimpanzees | |
| Much larger brains Brain size roughly tripled over the last 2 to 3 million years. | Nerves and senses | about 2 million years ago | Our line, since the split with chimpanzees | |
| Control of fire Evidence for regular use of fire ranges from about 1 million to a few hundred thousand years ago and is debated. (timing or placement uncertain) | Behavior and culture | about 1 million years ago | Our line, since the split with chimpanzees | |
| Spoken language When language arose is unknown, because speech does not fossilize. (timing or placement uncertain) | Behavior and culture | about 0.3 million years ago | Our line, since the split with chimpanzees | |
| Symbolic art and ornament Engraved ochre and shell beads appear by about 100,000 years ago. | Behavior and culture | about 0.1 million years ago | Our line, since the split with chimpanzees | |
| Knuckle-walking Shared with gorillas, but it may have evolved separately in the two. (evolved more than once; timing or placement uncertain) | Body plan | since about 6.5 million years ago, on their own branch | Chimpanzees and bonobos | |
| Very large body size with strong size differences between males and females | Body plan | since about 9 million years ago, on their own branch | Gorillas | |
| Slow life history: long childhoods and long lives Shared by all great apes and taken further in humans. (timing or placement uncertain) | Reproduction and development | between about 15 million and 19 million years ago | Our line, by rendezvous 3 | |
| Largely solitary life in the tree canopy | Behavior and culture | since about 15 million years ago, on their own branch | Orangutans | |
| Loss of the tail (a loss) | Body plan | between about 19 million and 29 million years ago | Our line, by rendezvous 4 | |
| Flexible shoulders for hanging below branches Taken to an extreme by gibbons. (timing or placement uncertain) | Body plan | between about 19 million and 29 million years ago | Our line, by rendezvous 4 | |
| Swinging arm over arm through the trees (brachiation) | Body plan | since about 19 million years ago, on their own branch | Gibbons | |
| Loud, elaborate songs | Behavior and culture | since about 19 million years ago, on their own branch | Gibbons | |
| Routine three-color (trichromatic) vision (evolved more than once) | Nerves and senses | between about 29 million and 40 million years ago | Our line, by rendezvous 5 | |
| Cheek pouches for storing food Found in some Old World monkeys, such as macaques and baboons. | Body plan | since about 29 million years ago, on their own branch | Old World monkeys | |
| Eye sockets closed off at the back | Body plan | between about 40 million and 63 million years ago | Our line, by rendezvous 6 | |
| Grasping (prehensile) tails | Body plan | since about 40 million years ago, on their own branch | New World monkeys | |
| Loss of the ability to make vitamin C (a loss; evolved more than once) | Physiology and metabolism | between about 63 million and 72 million years ago | Our line, by rendezvous 7 | |
| A dry nose, without the moist, dog-like rhinarium (a loss) | Nerves and senses | between about 63 million and 72 million years ago | Our line, by rendezvous 7 | |
| Enormous eyes, each larger than the brain | Nerves and senses | since about 63 million years ago, on their own branch | Tarsiers | |
| A head that turns nearly 180 degrees | Body plan | since about 63 million years ago, on their own branch | Tarsiers | |
| Nails instead of claws on most fingers and toes | Body plan | between about 72 million and 80 million years ago | Our line, by rendezvous 8 | |
| Grasping hands and feet with an opposable big toe | Body plan | between about 72 million and 80 million years ago | Our line, by rendezvous 8 | |
| Forward-facing eyes with overlapping fields of view (evolved more than once) | Nerves and senses | between about 72 million and 80 million years ago | Our line, by rendezvous 8 | |
| A toothcomb of forward-pointing lower teeth, used in grooming | Body plan | since about 72 million years ago, on their own branch | Lemurs and lorises | |
| Gliding membranes (colugos) (evolved more than once) | Body plan | since about 80 million years ago, on their own branch | Colugos and tree shrews | |
| Ever-growing gnawing incisors | Body plan | since about 88 million years ago, on their own branch | Rodents and rabbits | |
| Powered flight (bats) (evolved more than once) | Body plan | since about 94 million years ago, on their own branch | Laurasiatheres | |
| Echolocation (bats and toothed whales) (evolved more than once) | Nerves and senses | since about 94 million years ago, on their own branch | Laurasiatheres | |
| A return to life in the sea (whales) | Body plan | since about 94 million years ago, on their own branch | Laurasiatheres | |
| Long pregnancy supported by an elaborate placenta Marsupials have a placenta too, but a short-lived one. (timing or placement uncertain) | Reproduction and development | between about 102 million and 160 million years ago | Our line, by rendezvous 12 | |
| A corpus callosum linking the two halves of the brain | Nerves and senses | between about 102 million and 160 million years ago | Our line, by rendezvous 12 | |
| A trunk (elephants) | Body plan | since about 102 million years ago, on their own branch | Afrotheres and xenarthrans | |
| Bony armor (armadillos) (evolved more than once) | Body plan | since about 102 million years ago, on their own branch | Afrotheres and xenarthrans | |
| Live birth without eggshells (evolved more than once) | Reproduction and development | between about 160 million and 180 million years ago | Our line, by rendezvous 13 | |
| Nipples (teats) | Reproduction and development | between about 160 million and 180 million years ago | Our line, by rendezvous 13 | |
| External ear flaps (pinnae) (timing or placement uncertain) | Nerves and senses | between about 160 million and 180 million years ago | Our line, by rendezvous 13 | |
| A pouch in many species | Reproduction and development | since about 160 million years ago, on their own branch | Marsupials | |
| Very short pregnancy followed by long nursing | Reproduction and development | since about 160 million years ago, on their own branch | Marsupials | |
| Hair (timing or placement uncertain) | Body plan | between about 180 million and 318 million years ago | Our line, by rendezvous 14 | |
| Milk and mammary glands | Reproduction and development | between about 180 million and 318 million years ago | Our line, by rendezvous 14 | |
| A lower jaw made of a single bone | Body plan | between about 180 million and 318 million years ago | Our line, by rendezvous 14 | |
| Three middle-ear bones Fossils suggest that the final arrangement evolved separately in monotremes and in the ancestors of marsupials and placentals. (evolved more than once) | Nerves and senses | between about 180 million and 318 million years ago | Our line, by rendezvous 14 | |
| Warm-bloodedness (endothermy) (evolved more than once; timing or placement uncertain) | Physiology and metabolism | between about 180 million and 318 million years ago | Our line, by rendezvous 14 | |
| Electroreception in the bill (platypus) (evolved more than once) | Nerves and senses | since about 180 million years ago, on their own branch | Monotremes | |
| Venomous spurs (male platypus) | Body plan | since about 180 million years ago, on their own branch | Monotremes | |
| The amniotic egg | Reproduction and development | between about 318 million and 350 million years ago | Our line, by rendezvous 15 | |
| Tough, waterproof skin | Body plan | between about 318 million and 350 million years ago | Our line, by rendezvous 15 | |
| Breathing by expanding the rib cage (timing or placement uncertain) | Physiology and metabolism | between about 318 million and 350 million years ago | Our line, by rendezvous 15 | |
| Feathers and flight (birds) (evolved more than once) | Body plan | since about 318 million years ago, on their own branch | Reptiles and birds | |
| Shells (turtles) | Body plan | since about 318 million years ago, on their own branch | Reptiles and birds | |
| Limbs with fingers and toes | Body plan | between about 350 million and 408 million years ago | Our line, by rendezvous 16 | |
| A neck, letting the head turn independently of the body | Body plan | between about 350 million and 408 million years ago | Our line, by rendezvous 16 | |
| Breathing through the skin | Physiology and metabolism | since about 350 million years ago, on their own branch | Amphibians | |
| Metamorphosis from tadpole to adult (frogs) | Reproduction and development | since about 350 million years ago, on their own branch | Amphibians | |
| Surviving drought in a mucus cocoon (African lungfish) | Physiology and metabolism | since about 408 million years ago, on their own branch | Lungfish | |
| Fleshy, lobed fins with a single bone at the base | Body plan | between about 415 million and 430 million years ago | Our line, by rendezvous 18 | |
| Bone replacing cartilage in the internal skeleton | Body plan | between about 430 million and 460 million years ago | Our line, by rendezvous 19 | |
| Lungs | Physiology and metabolism | between about 430 million and 460 million years ago | Our line, by rendezvous 19 | |
| A gas-filled swim bladder for buoyancy | Physiology and metabolism | since about 430 million years ago, on their own branch | Ray-finned fishes | |
| Jaws Derived from gill-arch supports. | Body plan | between about 460 million and 550 million years ago | Our line, by rendezvous 20 | |
| Paired pelvic fins (the forerunners of legs) | Body plan | between about 460 million and 550 million years ago | Our line, by rendezvous 20 | |
| Adaptive immunity with antibodies and T cells (evolved more than once) | Cells and molecules | between about 460 million and 550 million years ago | Our line, by rendezvous 20 | |
| Electroreception (sharks and rays) The platypus evolved electroreception separately. (evolved more than once) | Nerves and senses | since about 460 million years ago, on their own branch | Sharks and rays | |
| A skull (cranium) | Body plan | between about 550 million and 590 million years ago | Our line, by rendezvous 21 | |
| Neural crest cells | Reproduction and development | between about 550 million and 590 million years ago | Our line, by rendezvous 21 | |
| Camera-type eyes (evolved more than once) | Nerves and senses | between about 550 million and 590 million years ago | Our line, by rendezvous 21 | |
| Whole-genome duplications At least one doubling of the entire genome happened on this stretch; how many, and when, is debated. (timing or placement uncertain) | Cells and molecules | between about 550 million and 590 million years ago | Our line, by rendezvous 21 | |
| A separate adaptive immune system (variable lymphocyte receptors) (evolved more than once) | Cells and molecules | since about 550 million years ago, on their own branch | Lampreys and hagfish | |
| Defensive slime (hagfish) | Physiology and metabolism | since about 550 million years ago, on their own branch | Lampreys and hagfish | |
| Forerunners of neural crest and placode cells Tunicate embryos have cells resembling both, the vertebrate cell types that build much of the head and its sense organs. (timing or placement uncertain) | Reproduction and development | between about 590 million and 600 million years ago | Our line, by rendezvous 22 | |
| A tunic made of cellulose | Cells and molecules | since about 590 million years ago, on their own branch | Tunicates (sea squirts) | |
| A notochord A flexible supporting rod, replaced by the backbone in most vertebrates. | Body plan | between about 600 million and 610 million years ago | Our line, by rendezvous 23 | |
| A hollow nerve cord along the back | Nerves and senses | between about 600 million and 610 million years ago | Our line, by rendezvous 23 | |
| A tail extending past the anus | Body plan | between about 600 million and 610 million years ago | Our line, by rendezvous 23 | |
| An endostyle, the forerunner of the thyroid gland | Physiology and metabolism | between about 600 million and 610 million years ago | Our line, by rendezvous 23 | |
| Pharyngeal (gill) slits (timing or placement uncertain) | Body plan | between about 610 million and 620 million years ago | Our line, by rendezvous 24 | |
| Five-part (pentaradial) adult symmetry | Body plan | since about 610 million years ago, on their own branch | Echinoderms and acorn worms | |
| A water-vascular system with tube feet | Physiology and metabolism | since about 610 million years ago, on their own branch | Echinoderms and acorn worms | |
| A through-gut with a separate mouth and anus (timing or placement uncertain) | Body plan | between about 620 million and 650 million years ago | Our line, by rendezvous 25 | |
| Excretory organs (nephridia) (timing or placement uncertain) | Physiology and metabolism | between about 620 million and 650 million years ago | Our line, by rendezvous 25 | |
| A jointed exoskeleton that is molted (arthropods) | Body plan | since about 620 million years ago, on their own branch | Protostomes | |
| Camera-type eyes (octopus and squid) (evolved more than once) | Nerves and senses | since about 620 million years ago, on their own branch | Protostomes | |
| Bilateral symmetry with a front and a back end Some cnidarians have a degree of bilateral symmetry too. (timing or placement uncertain) | Body plan | between about 650 million and 680 million years ago | Our line, by rendezvous 26 | |
| A third tissue layer (mesoderm) | Reproduction and development | between about 650 million and 680 million years ago | Our line, by rendezvous 26 | |
| Nerves concentrated at the front end (timing or placement uncertain) | Nerves and senses | between about 650 million and 680 million years ago | Our line, by rendezvous 26 | |
| Neurons and synapses (evolved more than once; timing or placement uncertain) | Nerves and senses | between about 680 million and 720 million years ago | Our line, by rendezvous 27 | |
| Hox and ParaHox body-patterning genes (timing or placement uncertain) | Reproduction and development | between about 680 million and 720 million years ago | Our line, by rendezvous 27 | |
| Stinging cells (cnidocytes) | Cells and molecules | since about 680 million years ago, on their own branch | Cnidarians | |
| Alternation between polyp and medusa stages | Reproduction and development | since about 680 million years ago, on their own branch | Cnidarians | |
| An extremely simple body with only a handful of cell types | Body plan | since about 720 million years ago, on their own branch | Placozoans | |
| Distinctive fusions of ancestral chromosomes Shared by sponges and all animals closer to us, and a key line of evidence that comb jellies branched off first (Schultz et al. 2023). (timing or placement uncertain) | Cells and molecules | between about 750 million and 780 million years ago | Our line, by rendezvous 29 | |
| A canal system lined with collared cells (choanocytes) | Body plan | since about 750 million years ago, on their own branch | Sponges | |
| Skeletons of glassy or chalky spicules | Body plan | since about 750 million years ago, on their own branch | Sponges | |
| Multicellularity with many specialized cell types (evolved more than once) | Cells and molecules | between about 780 million and 850 million years ago | Our line, by rendezvous 30 | |
| Eggs and sperm, and embryos that develop from a hollow ball of cells (timing or placement uncertain) | Reproduction and development | between about 780 million and 850 million years ago | Our line, by rendezvous 30 | |
| Collagen scaffolding between cells | Cells and molecules | between about 780 million and 850 million years ago | Our line, by rendezvous 30 | |
| Combs of fused cilia for swimming | Body plan | since about 780 million years ago, on their own branch | Comb jellies | |
| Sticky cells (colloblasts) for catching prey | Cells and molecules | since about 780 million years ago, on their own branch | Comb jellies | |
| A collar of microvilli around a single flagellum (timing or placement uncertain) | Cells and molecules | between about 850 million and 950 million years ago | Our line, by rendezvous 31 | |
| Cadherin adhesion proteins and tyrosine-kinase signaling | Cells and molecules | between about 850 million and 950 million years ago | Our line, by rendezvous 31 | |
| Rosette colonies triggered by bacteria (in some species) | Cells and molecules | since about 850 million years ago, on their own branch | Choanoflagellates | |
| Integrin adhesion proteins (timing or placement uncertain) | Cells and molecules | between about 950 million and 1.1 billion years ago | Our line, by rendezvous 32 | |
| Cells that aggregate into temporary multicellular clumps (Capsaspora) | Cells and molecules | since about 950 million years ago, on their own branch | Filastereans and ichthyosporeans | |
| A single flagellum at the rear of swimming cells | Cells and molecules | between about 1.1 billion and 1.25 billion years ago | Our line, by rendezvous 33 | |
| Hyphae and external digestion | Body plan | since about 1.1 billion years ago, on their own branch | Fungi | |
| Cell walls of chitin | Cells and molecules | since about 1.1 billion years ago, on their own branch | Fungi | |
| Aggregating into a multicellular slug (cellular slime molds) One of several separate origins of multicellularity. (evolved more than once) | Cells and molecules | since about 1.25 billion years ago, on their own branch | Amoebozoans | |
| A nucleus | Cells and molecules | between about 1.6 billion and 2.3 billion years ago | Our line, by rendezvous 35 | |
| Mitochondria, from an engulfed alphaproteobacterium | Cells and molecules | between about 1.6 billion and 2.3 billion years ago | Our line, by rendezvous 35 | |
| Mitosis, meiosis, and sex | Reproduction and development | between about 1.6 billion and 2.3 billion years ago | Our line, by rendezvous 35 | |
| Internal membranes: endoplasmic reticulum and Golgi apparatus | Cells and molecules | between about 1.6 billion and 2.3 billion years ago | Our line, by rendezvous 35 | |
| The eukaryotic flagellum (cilium), with its 9 + 2 arrangement | Cells and molecules | between about 1.6 billion and 2.3 billion years ago | Our line, by rendezvous 35 | |
| Genes interrupted by introns and spliced by the spliceosome | Cells and molecules | between about 1.6 billion and 2.3 billion years ago | Our line, by rendezvous 35 | |
| Chloroplasts, from an engulfed cyanobacterium (plants and algae) Later passed on to other eukaryotes by further engulfments. | Cells and molecules | since about 1.6 billion years ago, on their own branch | Plants, algae, and all other eukaryotes | |
| Cellulose cell walls (plants) | Cells and molecules | since about 1.6 billion years ago, on their own branch | Plants, algae, and all other eukaryotes | |
| “Eukaryotic signature proteins” for shaping membranes and the cytoskeleton (timing or placement uncertain) | Cells and molecules | between about 2.3 billion and 3.5 billion years ago | Our line, by rendezvous 36 | |
| Long, thin cell extensions (Prometheoarchaeum) | Cells and molecules | since about 2.3 billion years ago, on their own branch | Asgard archaea | |
| Histone proteins that package DNA Found in many archaea and in all eukaryotes. (timing or placement uncertain) | Cells and molecules | between about 3.5 billion and 4.2 billion years ago | Our line, by rendezvous 37 | |
| Making methane (methanogenesis) Known only from archaea. | Physiology and metabolism | since about 3.5 billion years ago, on their own branch | Other archaea | |
| Membranes built from ether-linked lipids | Cells and molecules | since about 3.5 billion years ago, on their own branch | Other archaea | |
| The genetic code | Cells and molecules | before about 4.2 billion years ago | Our line, by rendezvous 38 | |
| Ribosomes and protein synthesis | Cells and molecules | before about 4.2 billion years ago | Our line, by rendezvous 38 | |
| ATP synthase driven by ion gradients across a membrane | Physiology and metabolism | before about 4.2 billion years ago | Our line, by rendezvous 38 | |
| A DNA genome Bacteria and archaea copy DNA with largely unrelated enzymes, so whether LUCA had a DNA genome is debated. (timing or placement uncertain) | Cells and molecules | before about 4.2 billion years ago | Our line, by rendezvous 38 | |
| A cell membrane Bacterial and archaeal membranes are built differently, so the nature of LUCA’s membrane is debated. (timing or placement uncertain) | Cells and molecules | before about 4.2 billion years ago | Our line, by rendezvous 38 | |
| Oxygen-producing photosynthesis (cyanobacteria) The source of the oxygen that began building up about 2.4 billion years ago. | Physiology and metabolism | since about 4.2 billion years ago, on their own branch | Bacteria | |
| Peptidoglycan cell walls | Cells and molecules | since about 4.2 billion years ago, on their own branch | Bacteria |
⏳ Deep Time
Millions and billions of years are hard to picture. Carl Sagan’s Cosmic Calendar, from his book The Dragons of Eden (1977), squeezed the history of the universe into a single year. Here the same idea is applied to the history of Earth and of life, with a choice of starting points and of what to squeeze it into.
| Event | When | World population | On the calendar |
|---|---|---|---|
| Earth forms | about 4.54 billion years ago | ||
| Oldest known mineral grains (zircons) | about 4.4 billion years ago | ||
| LUCA, by one recent estimate | about 4.2 billion years ago | ||
| Oldest widely accepted stromatolites | about 3.48 billion years ago | ||
| Oxygen begins to build up (Great Oxidation Event) | about 2.4 billion years ago | ||
| LECA, roughly | about 1.6 billion years ago | ||
| Bangiomorpha, an early red alga | about 1.05 billion years ago | ||
| “Snowball Earth” glaciations (about 720 to 635 million years ago) | about 700 million years ago | ||
| Ediacaran organisms appear | about 571 million years ago | ||
| Cambrian explosion begins | about 539 million years ago | ||
| Oldest plant spores on land | about 470 million years ago | ||
| Tiktaalik | about 375 million years ago | ||
| End-Permian mass extinction | about 252 million years ago | ||
| Morganucodon, a close relative of mammals | about 205 million years ago | ||
| Asteroid impact ends the age of dinosaurs | about 66 million years ago | ||
| Our split from chimpanzees, roughly | about 6.5 million years ago | ||
| Lucy | about 3.2 million years ago | ||
| Pleistocene ice ages begin | about 2.58 million years ago | ||
| Hominins leave Africa (Dmanisi) | about 1.8 million years ago | ||
| Oldest fossils of our species | about 300,000 years ago | ||
| Oldest widely accepted intentional burials | about 100,000 years ago | ||
| Oldest known figurative cave paintings | about 45,000 years ago | ||
| Last ice age ends; Holocene begins; farming soon follows | about 11,700 years ago | perhaps 5 million | |
| Writing is invented | about 5,200 years ago | ||
| Aristotle is born | 384 BCE | about 160 million | |
| Magna Carta | 1215 | about 400 million | |
| Declaration of Independence | 1776 | about 800 million | |
| World population reaches 1 billion | 1804 | 1 billion | |
| Darwin’s On the Origin of Species | 1859 | about 1.2 billion | |
| First powered airplane flight | 1903 | about 1.6 billion | |
| Félix d’Hérelle names the bacteriophages | 1917 | about 1.9 billion | |
| World population reaches 2 billion | 1927 | 2 billion | |
| End of World War II; first atomic bombs | 1945 | about 2.3 billion | |
| Structure of DNA described | 1953 | about 2.7 billion | |
| Brown v. Board of Education | 1954 | about 2.7 billion | |
| First human in space; the Beatles are not far behind | 1961 | about 3.1 billion | |
| Hand-held calculators become common | 1975 | about 4.1 billion | |
| Personal computers spread | 1985 | about 4.9 billion | |
| World Wide Web goes public | 1991 | about 5.4 billion | |
| Smartphones | 2007 | about 6.7 billion | |
| World population reaches 8 billion | 2022 | 8 billion |
Several of these dates are estimates with wide uncertainty, especially the older ones; see How We Know. Population figures before about 1950 are rough estimates. Almost all of recorded history, from Aristotle to today, fits into the last few seconds of the year.
🦴 Relatives, Not Ancestors
A fossil can almost never be shown to be an actual ancestor of anything living. What a fossil can show is what the relatives of our ancestors were like at a particular time. Most fossils described as “links” are better understood as members of side branches that split off near the point of interest, which is why this page lists fossils as coming from a stretch of time rather than as stops on the walk.
Tiktaalik is a good example. It is a superb intermediate between fish and four-limbed animals, yet trackways left by four-limbed animals in Poland are older than it is, so Tiktaalik must be a late-surviving member of a lineage close to our ancestors, not the ancestor itself. Some claims go further and fall apart: Darwinius (“Ida”) was presented in 2009 as a link to our own lineage, and Saccorhytus in 2017 as the earliest known deuterostome, but later work placed each on a different branch.
Living organisms are cousins, not ancestors. A chimpanzee is not a stage we passed through, and a sponge is not a primitive animal waiting to become something else. Every lineage alive today has been evolving for exactly as long as ours has, about 4 billion years.
⏱️ Where the Dates Come From
Most of the dates on this page come from molecular clocks. Differences between the DNA or protein sequences of two species accumulate roughly in proportion to the time since they split, so, once calibrated against fossils of known age, sequence differences can be converted into dates. The ticking is irregular, though, and the answer depends on which fossils are used for calibration and how the variation in rates is modeled, so different studies give different dates. The ranges given here are rounded from published estimates, many of which can be explored at TimeTree (Kumar et al. 2022).
Clock dates are usually older than the oldest fossils of a group. That is expected: the first members of a new lineage are few, and often small or soft, so they are rarely preserved and even more rarely found. The first fossil marks the latest a group could have begun, not the earliest.
🌳 Why the Deepest Branches Are Blurry
Near the base of the tree, three problems pile up. Signals in sequences are overwritten by later changes, so very old splits become hard to resolve. Genes also move between distantly related organisms by horizontal gene transfer, especially among bacteria and archaea, so different genes can tell different stories. And eukaryotes have more than one ancestry: our host-cell line goes back through the archaea, while our mitochondria descend from a captured bacterium. Plants and algae add a third line, through the cyanobacteria that became chloroplasts. For these reasons the deepest part of the tree looks less like a tree and more like a web, and the order of the last few rendezvous on this walk is the least certain part of it.
👥 Concestors Were Populations
Each concestor stands for an ancestral population, not a single animal or cell, and splits between lineages took time. Genes can also sort into descendant species in unexpected ways, which is why, for some stretches of DNA, gorillas are closer to us than chimpanzees are, even though chimpanzees are our closest relatives overall.
🏷️ Names and Ranks
Traditional classification sorts organisms into nested ranks: domain, kingdom, phylum, class, order, family, genus, and species, with many sub- and super- ranks added over the years. The ranks were set up long before evolutionary relationships were well understood, and they do not line up with the rendezvous. Mammals and birds are each a class, for example, yet birds belong within the reptiles, so the reptiles as traditionally defined, without birds, are not a complete branch of the tree. Many rendezvous have a name but no rank at all. Each rendezvous card gives the name of the group descended from its concestor and, where there is one, its traditional rank.
🧩 Placing the Innovations
An innovation is placed at the oldest concestor that probably had it, based on which of its descendants have it today and on fossils where they help. That tells us the innovation arose somewhere along the stretch before that concestor, not exactly when. Innovations that evolved more than once are flagged, because a trait shared by two groups does not always mean it was inherited from their concestor. The lists are selective: every stretch of the walk saw many more changes than are listed here.
Finally, the walk starts with us only because we are the ones asking. As Dawkins points out, any living species could make the same pilgrimage, and all of the pilgrims would arrive at LUCA in the end.
📚 References
- Daeschler, E.B., Shubin, N.H., & Jenkins, F.A., Jr. (2006). A Devonian tetrapod-like fish and the evolution of the tetrapod body plan. Nature, 440, 757–763. doi:10.1038/nature04639
- Dawkins, R. (2004). The Ancestor’s Tale: A Pilgrimage to the Dawn of Life. Boston: Houghton Mifflin.
- Dawkins, R., & Wong, Y. (2016). The Ancestor’s Tale: A Pilgrimage to the Dawn of Evolution (2nd ed.). Boston: Mariner Books.
- Delsuc, F., Brinkmann, H., Chourrout, D., & Philippe, H. (2006). Tunicates and not cephalochordates are the closest living relatives of vertebrates. Nature, 439, 965–968. doi:10.1038/nature04336
- Eme, L., Tamarit, D., Caceres, E.F., Stairs, C.W., De Anda, V., Schön, M.E., Seitz, K.W., Dombrowski, N., Lewis, W.H., Homa, F., Saw, J.H., Lombard, J., Nunoura, T., Li, W.-J., Hua, Z.-S., Chen, L.-X., Banfield, J.F., St John, E., Reysenbach, A.-L., Stott, M.B., Schramm, A., Kjeldsen, K.U., Teske, A.P., Baker, B.J., & Ettema, T.J.G. (2023). Inference and reconstruction of the heimdallarchaeial ancestry of eukaryotes. Nature, 618, 992–999. doi:10.1038/s41586-023-06186-2
- Franzen, J.L., Gingerich, P.D., Habersetzer, J., Hurum, J.H., von Koenigswald, W., & Smith, B.H. (2009). Complete primate skeleton from the Middle Eocene of Messel in Germany: Morphology and paleobiology. PLoS ONE, 4, e5723. doi:10.1371/journal.pone.0005723
- Kumar, S., Suleski, M., Craig, J.M., Kasprowicz, A.E., Sanderford, M., Li, M., Stecher, G., & Hedges, S.B. (2022). TimeTree 5: An expanded resource for species divergence times. Molecular Biology and Evolution, 39, msac174. doi:10.1093/molbev/msac174
- Liu, Y., Carlisle, E., Zhang, H., Yang, B., Steiner, M., Shao, T., Duan, B., Marone, F., Xiao, S., & Donoghue, P.C.J. (2022). Saccorhytus is an early ecdysozoan and not the earliest deuterostome. Nature, 609, 541–546. doi:10.1038/s41586-022-05107-z
- Moody, E.R.R., Álvarez-Carretero, S., Mahendrarajah, T.A., Clark, J.W., Betts, H.C., Dombrowski, N., Szánthó, L.L., Boyle, R.A., Daines, S., Chen, X., Lane, N., Yang, Z., Shields, G.A., Szöllősi, G.J., Spang, A., Pisani, D., Williams, T.A., Lenton, T.M., & Donoghue, P.C.J. (2024). The nature of the last universal common ancestor and its impact on the early Earth system. Nature Ecology & Evolution, 8, 1654–1666. doi:10.1038/s41559-024-02461-1
- Rohde, D.L.T., Olson, S., & Chang, J.T. (2004). Modelling the recent common ancestry of all living humans. Nature, 431, 562–566. doi:10.1038/nature02842
- Sagan, C. (1977). The Dragons of Eden: Speculations on the Evolution of Human Intelligence. New York: Random House.
- Schultz, D.T., Haddock, S.H.D., Bredeson, J.V., Green, R.E., Simakov, O., & Rokhsar, D.S. (2023). Ancient gene linkages support ctenophores as sister to other animals. Nature, 618, 110–117. doi:10.1038/s41586-023-05936-6
🧪 LUCA Was Not the Beginning
LUCA is the most recent ancestor of everything alive today, not the first living thing. By the time of LUCA, cells already had a genetic code, ribosomes, and hundreds to thousands of genes, and some of those genes had already been duplicated and diverged into families before LUCA lived. The study that placed LUCA at about 4.2 billion years ago used exactly those pre-LUCA gene duplicates to date it (Moody et al. 2024). So a great deal of evolution happened before LUCA, on lineages that have left no separate descendants. Everything on this tab is hypothesis, with the evidence growing thinner the further back it reaches.
If LUCA really lived 4.2 billion years ago, that leaves only a few hundred million years after Earth formed, 4.54 billion years ago, for life to begin and evolve to LUCA’s level of complexity. Mineral grains called zircons suggest that liquid water was present by about 4.4 billion years ago.
🧬 Progenotes and the RNA World
Carl Woese, who first recognized the archaea as a separate group of organisms, called the hypothetical ancestors before LUCA progenotes: entities in which the link between genes and the proteins they encode was still crude and imprecise.
Further back still may lie an RNA world, a name given by Walter Gilbert (1986) to a time when RNA served both as the genetic material and as the catalyst, roles now divided between DNA and proteins. The idea is supported by the discovery of catalytic RNAs (ribozymes) and, most strikingly, by the ribosome itself, whose core, the part that joins amino acids into proteins, is made of RNA rather than protein. How an RNA world could have arisen from simpler chemistry is still an open problem.
🌊 Where Did Life Begin?
Charles Darwin speculated, in an 1871 letter to Joseph Hooker, about a “warm little pond” rich in chemicals, light, heat, and electricity. Modern candidates include pools on land that repeatedly dried and rewetted, and deep-sea hydrothermal vents, where natural gradients of acidity and chemical energy resemble the ion gradients that every cell, LUCA included, uses to make ATP; the vent hypotheses have been developed by Michael Russell, William Martin, and Nick Lane, among others. The idea that life arrived from elsewhere in space, panspermia, does not answer the question so much as move it somewhere else.
🦠 Viruses at the Root
Viruses are not on the tree of cellular life, but they may be as old as the tree itself. Some virus proteins, including a common type of capsid protein, are shared by viruses infecting bacteria, archaea, and eukaryotes, which suggests that virus lineages were already present in the time of LUCA. One proposal is that viruses descend from primordial genetic elements that picked up capsid proteins from their cellular hosts (Krupovic et al. 2019). The reconstruction of LUCA as carrying antiviral defenses (Moody et al. 2024) points the same way. If so, the bacteriophages infecting the bacteria that join us at rendezvous 38 may belong to lineages that are older than LUCA itself.
📚 References
- Gilbert, W. (1986). Origin of life: The RNA world. Nature, 319, 618. doi:10.1038/319618a0
- Krupovic, M., Dolja, V.V., & Koonin, E.V. (2019). Origin of viruses: Primordial replicators recruiting capsids from hosts. Nature Reviews Microbiology, 17, 449–458. doi:10.1038/s41579-019-0205-6
- Moody, E.R.R., Álvarez-Carretero, S., Mahendrarajah, T.A., Clark, J.W., Betts, H.C., Dombrowski, N., Szánthó, L.L., Boyle, R.A., Daines, S., Chen, X., Lane, N., Yang, Z., Shields, G.A., Szöllősi, G.J., Spang, A., Pisani, D., Williams, T.A., Lenton, T.M., & Donoghue, P.C.J. (2024). The nature of the last universal common ancestor and its impact on the early Earth system. Nature Ecology & Evolution, 8, 1654–1666. doi:10.1038/s41559-024-02461-1