Timeline of human evolution

Haeckel's Paleontological Tree of Vertebrates (c. 1879). The evolutionary history of species has been described as a "tree" with many branches arising from a single trunk. While Haeckel's tree is somewhat outdated, it illustrates clearly the principles that more complex modern reconstructions can obscure.

The timeline of human evolution outlines the major events in the development of the human species, Homo sapiens, and the evolution of human ancestors. It includes brief explanations of some of the species, genera, and the higher ranks of taxa that are seen today as possible ancestors of modern humans.

This timeline is based on studies from anthropology, paleontology, developmental biology, morphology, and from anatomical and genetic data. It does not address the origin of life, which discussion is provided by abiogenesis, but presents one possible line of evolutionary descent of species that eventually led to humans.

A caution: Other than Mr Haeckel's historic and emblematic "tree", this article provides no phylogenetics analysis to help portray the complex, nonlinear facts of human evolution. It is important that the "possible line of evolutionary descent" should not be interpreted as providing a linear progression from very early taxa to a (presupposed) objective of Homo sapiens; no such directed progression is implied here.

Taxonomy of Homo sapiens

One of several possible lines of descent, or taxonomic ranking, of Homo sapiens is shown below.

Life timeline

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water

Simple life

photosynthesis

Eukaryotes

Complex
multicellular life

Land animals

Land plants

Dinosaurs    

Mammals

Flowers

 

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Earliest Earth

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Earliest water

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Earliest life
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Meteorite bombardment

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Earliest oxygen

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Atmospheric oxygen

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Oxygen Crisis

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Earliest sexual reproduction

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Earliest land life

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Earliest humans

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Axis scale: Millions of years.
also see {{Nature timeline}}

Taxonomic rank	Name	Common name	Millions of years ago
Domain	Eukaryota	Cells with a nucleus	2,100
Kingdom	Animalia	Animals	590
Phylum	Chordata	Vertebrates and closely related invertebrates	530
Subphylum	Vertebrata	Vertebrates	505
Superclass	Tetrapoda	Tetrapods (animals with four limbs)	395
Unranked	Amniota	Amniotes (fully terrestrial tetrapods whose eggs are "equipped with an amnios")	340
Class	Mammalia	Mammals	220
Subclass	Theria	Mammals that give birth to live young (i.e., non-egg-laying)
Infraclass	Eutheria	Placental mammals (i.e., non-marsupials)	125
Magnorder	Boreoeutheria	Supraprimates, (most) hoofed mammals, (most) carnivorous mammals, whales, and bats
Superorder	Euarchontoglires	Supraprimates: primates, colugos, tree shrews, rodents, and rabbits	100
Grandorder	Euarchonta	Primates, colugos, and tree shrews
Mirorder	Primatomorpha	Primates and colugos	79.6
Order	Primates	Primates	75
Suborder	Haplorrhini	"Dry-nosed" (literally, "simple-nosed") primates: apes, monkeys, and tarsiers	40
Infraorder	Simiiformes	"Higher" primates (Simians): apes and monkeys
Parvorder	Catarrhini	"Downward-nosed" primates: apes and old-world monkeys	30
Superfamily	Hominoidea	Apes: great apes and lesser apes (gibbons)	28
Family	Hominidae	Great apes: humans, chimpanzees, gorillas, and orangutans—the hominids	15
Subfamily	Homininae	Humans, chimpanzees, and gorillas (the African apes)	8
Tribe	Hominini	Genera Homo, Pan, and the Australopithecines	5.8
Subtribe	Hominina	Genus Homo and close human relatives and ancestors after splitting from Pan—the hominins	2.5
Genus	Homo	Humans	2.5
Species	(Archaic) Homo sapiens	Neanderthals	0.5
Subspecies	Homo sapiens sapiens	Anatomically modern humans	0.2

Timeline

First living beings

Date	Event
4000 Ma (million years ago)	The earliest life appears.
3900 Ma	Cells resembling prokaryotes appear. This marks the first appearance of photosynthesis and therefore the first occurrence of large quantities of atmospheric oxygen on the earth.
2500 Ma	First organisms to utilize oxygen. By 2400 Ma, in what is referred to as the Great Oxygenation Event, the pre-oxygen anaerobic forms of life were wiped out by the oxygen consumers.
2100 Ma	More complex cells appear: the eukaryotes.
1200 Ma	Sexual reproduction evolves, leading to faster evolution[1] where genes are mixed in every generation enabling greater variation for subsequent selection.
900 Ma	Choanoflagellate The choanoflagellates may look similar to the ancestors of the entire animal kingdom, and in particular they may be the direct ancestors of sponges.[2][3] Proterospongia (members of the Choanoflagellata) are the best living examples of what the ancestor of all animals may have looked like. They live in colonies, and show a primitive level of cellular specialization for different tasks.
600 Ma	It is thought that the earliest multicellular animal was a sponge-like creature. Sponges are among the simplest of animals, with partially differentiated tissues. Sponges (Porifera) are the phylogenetically oldest animal phylum extant today.
580 Ma	Multicellular animal movement may have started with cnidarians. Almost all cnidarians possess nerves and muscles. Because they are the simplest animals to possess them, their direct ancestors were very probably the first animals to use nerves and muscles together. Cnidarians are also the first animals with an actual body of definite form and shape. They have radial symmetry. The first eyes evolved at this time.
550 Ma	Flatworm Flatworms are the earliest animals to have a brain, and the simplest animals alive to have bilateral symmetry. They are also the simplest animals with organs that form from three germ layers. Most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion.
540 Ma	Acorn worms are considered more highly specialised and advanced than other similarly shaped worm-like creatures. They have a circulatory system with a heart that also functions as a kidney. Acorn worms have a gill-like structure used for breathing, a structure similar to that of primitive fish. Acorn worms are thus sometimes said to be a link between vertebrates and invertebrates.

Chordates

Date	Event
530 Ma	Pikaia Pikaia is an iconic ancestor of modern chordates and vertebrates.[4] Other, earlier chordate predecessors include Myllokunmingia fengjiaoa,[5] Haikouella lanceolata,[6] and Haikouichthys ercaicunensis.[7] The lancelet, still living today, retains some characteristics of the primitive chordates. It resembles Pikaia. Conodont Conodonts are a famous type of early (495 Mya and later) chordate fossil; they have the peculiar teeth of an eel-shaped animal characterized by large eyes, fins with fin rays, chevron-shaped muscles and a notochord. The animal is sometimes called a conodont, and sometimes a conodontophore (conodont-bearer) to avoid confusion.
505 Ma	Agnatha The first vertebrates appear: the ostracoderms, jawless fish related to present-day lampreys and hagfishes. Haikouichthys and Myllokunmingia are examples of these jawless fish, or Agnatha. (See also prehistoric fish). They were jawless and their internal skeletons were cartilaginous. They lacked the paired (pectoral and pelvic) fins of more advanced fish. They were precursors to the Osteichthyes (bony fish).[8]
480 Ma	A placoderm The Placodermi were prehistoric fishes. Placoderms were some of the first jawed fishes (Gnathostomata), their jaws evolving from the first gill arch.[9] A placoderm's head and thorax were covered by articulated armoured plates and the rest of the body was scaled or naked. However, the fossil record indicates that they left no descendents after the end of the Devonian and are less closely related to living bony fishes than sharks are.
410 Ma	The first coelacanth appears;[10] this order of animals had been thought to have no extant members until living specimens were discovered in 1938. It is often referred to as a living fossil.

Tetrapods

Date	Event
390 Ma	Panderichthys Some fresh water lobe-finned fish (Sarcopterygii) develop legs and give rise to the Tetrapoda. The first tetrapods evolved in shallow and swampy freshwater habitats. Primitive tetrapods developed from a lobe-finned fish (an "osteolepid Sarcopterygian"), with a two-lobed brain in a flattened skull, a wide mouth and a short snout, whose upward-facing eyes show that it was a bottom-dweller, and which had already developed adaptations of fins with fleshy bases and bones. (The "living fossil" coelacanth is a related lobe-finned fish without these shallow-water adaptations.) Tetrapod fishes used their fins as paddles in shallow-water habitats choked with plants and detritus. The universal tetrapod characteristics of front limbs that bend backward at the elbow and hind limbs that bend forward at the knee can plausibly be traced to early tetrapods living in shallow water.[11] [11] Panderichthys is a 90–130 cm (35–50 in) long fish from the Late Devonian period (380 Mya). It has a large tetrapod-like head. Panderichthys exhibits features transitional between lobe-finned fishes and early tetrapods. Trackway impressions made by something that resembles Ichthyostega's limbs were formed 390 Ma in Polish marine tidal sediments. This suggests tetrapod evolution is older than the dated fossils of Panderichthys through to Ichthyostega. Lungfishes retain some characteristics of the early Tetrapoda. One example is the Queensland lungfish.
375 Ma	Tiktaalik Tiktaalik is a genus of sarcopterygian (lobe-finned) fishes from the late Devonian with many tetrapod-like features. It shows a clear link between Panderichthys and Acanthostega.
365 Ma	Acanthostega Ichthyostega Acanthostega is an extinct amphibian, among the first animals to have recognizable limbs. It is a candidate for being one of the first vertebrates to be capable of coming onto land. It lacked wrists, and was generally poorly adapted for life on land. The limbs could not support the animal's weight. Acanthostega had both lungs and gills, also indicating it was a link between lobe-finned fish and terrestrial vertebrates. Ichthyostega is an early tetrapod. Being one of the first animals with legs, arms, and finger bones, Ichthyostega is seen as a hybrid between a fish and an amphibian. Ichthyostega had legs but its limbs probably weren't used for walking. They may have spent very brief periods out of water and would have used their legs to paw their way through the mud.[12] Amphibia were the first four-legged animals to develop lungs which may have evolved from Hynerpeton 360 Mya. Amphibians living today still retain many characteristics of the early tetrapods.
300 Ma	Hylonomus From amphibians came the first reptiles: Hylonomus is the earliest known reptile. It was 20 cm (8 in) long (including the tail) and probably would have looked rather similar to modern lizards. It had small sharp teeth and probably ate millipedes and early insects. It is a precursor of later Amniotes and mammal-like reptiles. Αlpha keratin first evolves here which is used in claws in modern lizards and birds, and hair in mammals.[13] Evolution of the amniotic egg gives rise to the Amniota, reptiles that can reproduce on land and lay eggs on dry land. They did not need to return to water for reproduction. This adaptation gave them the capability to colonize the uplands for the first time. Reptiles have advanced nervous systems, compared to amphibians. They have twelve pairs of cranial nerves.

Mammals

Date	Event
256 Ma	Phthinosuchus, an early Therapsid Shortly after the appearance of the first reptiles, two branches split off. One branch is the Sauropsids, from which come the modern reptiles and birds. The other branch is Synapsida, from which come modern mammals. Both had temporal fenestrae, a pair of holes in their skulls behind the eyes, which were used to increase the space for jaw muscles. Synapsids had one opening on each side, while diapsids had two. The earliest mammal-like reptiles are the pelycosaurs. The pelycosaurs were the first animals to have temporal fenestrae. Pelycosaurs are not therapsids but soon they gave rise to them. The Therapsida were the direct ancestor of mammals. The therapsids have temporal fenestrae larger and more mammal-like than pelycosaurs, their teeth show more serial differentiation, and later forms had evolved a secondary palate. A secondary palate enables the animal to eat and breathe at the same time and is a sign of a more active, perhaps warm-blooded, way of life.[14]
220 Ma	Cynognathus One sub-group of therapsids, the cynodonts, evolved more mammal-like characteristics. The jaws of cynodonts resemble modern mammal jaws. It is very likely that this group of animals contains a species which is the direct ancestor of all modern mammals.[15]
220 Ma	Repenomamus From Eucynodontia (cynodonts) came the first mammals. Most early mammals were small shrew-like animals that fed on insects. Although there is no evidence in the fossil record, it is likely that these animals had a constant body temperature and milk glands for their young. The neocortex region of the brain first evolved in mammals and thus is unique to them. Monotremes are an egg-laying group of mammals represented amongst modern animals by the platypus and echidna. Recent genome sequencing of the platypus indicates that its sex genes are closer to those of birds than to those of the therian (live birthing) mammals. Comparing this to other mammals, it can be inferred that the first mammals to gain gender differentiation through the existence or lack of SRY gene (found in the y-Chromosome) evolved after the monotreme lineage split off.
160 Ma	Juramaia sinensis Juramaia sinensis[16] is the earliest known eutherian mammal fossil.
100 Ma	Last common ancestor of mice and humans (base of the clade Euarchontoglires).

Primates

Date	Event
85–65 Ma	Plesiadapis Carpolestes simpsoni A group of small, nocturnal and arboreal, insect-eating mammals called the Euarchonta begins a speciation that will lead to the primate, treeshrew and flying lemur orders. The Primatomorpha is a subdivision of Euarchonta that includes the primates and the stem-primates Plesiadapiformes. One of the early stem-primates is Plesiadapis. Plesiadapis still had claws and the eyes located on each side of the head. Because of this they were faster on the ground than on the top of the trees, but they began to spend long times on lower branches of trees, feeding on fruits and leaves. The Plesiadapiformes very likely contain the species which is the ancestor of all primates.[17] One of the last Plesiadapiformes is Carpolestes simpsoni. It had grasping digits but no forward-facing eyes.
63 Ma	Primates diverge into suborders Strepsirrhini (wet-nosed primates) and Haplorrhini (dry-nosed primates). Strepsirrhini contain most of the prosimians; modern examples include the lemurs and lorises. The haplorrhines include the three living groups: prosimian tarsiers, simian monkeys, and apes. One of the earliest haplorrhines is Teilhardina asiatica, a mouse-sized, diurnal creature with small eyes. The Haplorrhini metabolism lost the ability to make its own Vitamin C. This means that it and all its descendants had to include fruit in its diet, where Vitamin C could be obtained externally.
30 Ma	Aegyptopithecus Haplorrhini splits into infraorders Platyrrhini and Catarrhini. Platyrrhines, New World monkeys, have prehensile tails and males are color blind. They may have migrated to South America on a raft of vegetation across the relatively narrow Atlantic ocean (approx. 700 km). Catarrhines mostly stayed in Africa as the two continents drifted apart. Possible early ancestors of catarrhines include Aegyptopithecus and Saadanius.
25 Ma	Proconsul Catarrhini splits into 2 superfamilies, Old World monkeys (Cercopithecoidea) and apes (Hominoidea). Our trichromatic color vision had its genetic origins in this period. Proconsul was an early genus of catarrhine primates. They had a mixture of Old World monkey and ape characteristics. Proconsul's monkey-like features include thin tooth enamel, a light build with a narrow chest and short forelimbs, and an arboreal quadrupedal lifestyle. Its ape-like features are its lack of a tail, ape-like elbows, and a slightly larger brain relative to body size. Proconsul africanus is a possible ancestor of both great and lesser apes, including humans.

Hominidae

Date	Event
15 Ma	Hominidae (great apes) speciate from the ancestors of the gibbon (lesser apes).
13 Ma	Homininae ancestors speciate from the ancestors of the orangutan.[18] Pierolapithecus catalaunicus is believed to be a common ancestor of humans and the other great apes, or at least a species that brings us closer to a common ancestor than any previous fossil discovery. It had the special adaptations for tree climbing as do present-day humans and other great apes: a wide, flat rib cage, a stiff lower spine, flexible wrists, and shoulder blades that lie along its back.
10 Ma	The lineage currently represented by humans and the Pan genus (common chimpanzees and bonobos) speciates from the ancestors of the gorillas.
7 Ma	Sahelanthropus tchadensis The Hominina, a subtribe of Hominini who are closely related to or ancestors to humans, speciate from the ancestors of the chimpanzees. Both chimpanzees and humans have a larynx that repositions during the first two years of life to a spot between the pharynx and the lungs, indicating that the common ancestors have this feature, a precondition for vocalized speech in humans. The latest common ancestor of humans and chimpanzees lived around the time of Sahelanthropus tchadensis, ca. 7 Ma ; and S. tchadensis is sometimes claimed to be that last common ancestor of humans and chimpanzees, but the claim has not been established. The earliest known representative from the ancestral human line post-dating the separation with the chimpanzee lines is Orrorin tugenensis (Millennium Man, Kenya; ca. 6 Ma).
4.4 Ma	Ardipithecus is, or may be, a very early hominin genus (tribe Hominini and subtribe Hominina). Two species are described in the literature: A. ramidus, which lived about 4.4 million years ago[19] during the early Pliocene, and A. kadabba, dated to approximately 5.6 million years ago[20] (late Miocene). A. ramidus had a small brain, measuring between 300 and 350 cm^3. This is about the same size as the modern bonobo and female common chimpanzee brain; it is much smaller than the brain of australopithecines like Lucy (400 to 550 cm^3) and slightly over a fifth the size of the modern Homo sapiens brain. Ardipithecus was arboreal, meaning it lived largely in the forest where it competed with other forest animals for food, no doubt including the contemporary ancestor of the chimpanzees. Ardipithecus was probably bipedal as evidenced by its bowl shaped pelvis, the angle of its foramen magnum and its thinner wrist bones, though its feet were still adapted for grasping rather than walking for long distances.
3.6 Ma	Australopithecus afarensis A member of the Australopithecus afarensis left human-like footprints on volcanic ash in Laetoli, Kenya (Northern Tanzania), providing strong evidence of full-time bipedalism. Australopithecus afarensis lived between 3.9 and 2.9 million years ago, and is considered one of the earliest hominins---those species that developed and comprised the lineage of ‘’Homo’’ and ‘’Homo’s’’ closest relatives after the split from the line of the chimpanzees. It is thought that A. afarensis was ancestral to both the genus Australopithecus and the genus Homo. Compared to the modern and extinct great apes, A. afarensis had reduced canines and molars, although they were still relatively larger than in modern humans. A. afarensis also has a relatively small brain size (380–430 cm³) and a prognathic (i.e. projecting anteriorly) face. Australopithecines have been found in savannah environments; from scavenging opportunities, they probably developed their diet to include meat. Analyses of Australopithecus africanus lower vertebrae suggests that these bones changed in females to support bipedalism even during pregnancy.
3.5-3.3 Ma	Kenyanthropus platyops, a possible ancestor of Homo, emerges from the Australopithecus genus. Stone tools are deliberately constructed.[21]
3 Ma	The bipedal australopithecines (a genus of the Hominina subtribe) evolve in the savannas of Africa being hunted by Dinofelis. Loss of body hair occurs from 3 to 2 Ma, in parallel with the development of full bipedalism.

Homo

Date	Event
2.8 Ma	Homo habilis Homo appears in East Africa; with most Australopithecines they are considered the first hominins—that is, they are designated (by some) as those earliest humans and human relatives or ancestors to rise after splitting from the lineage of Pan, the chimpanzees. Others consider the genus Pan as hominins also, and perhaps the first hominins. Sophisticated stone tools mark the beginning of the Lower Paleolithic. Homo habilis appears—the first, or one of the first, hominins to master stone tool technology. Stone tool implements also found along with Australopithecus garhi, dated to a slightly earlier period. Homo habilis, although significantly different of anatomy and physiology, is thought to be the ancestor of Homo ergaster, or African Homo erectus; but it is also known to have coexisted with Homo erectus for some one-half million years (until about 1.5 Ma).
1.8 Ma	A reconstruction of Homo erectus Homo erectus evolves in Africa. Homo erectus would bear a striking resemblance to modern humans, but had a brain about 74 percent of the size of modern man. Its forehead is less sloping than that of Homo habilis and the teeth are smaller. Homo ergaster, known as African Homo erectus, and other hominin species such as Homo georgicus, Homo pekinensis, Homo heidelbergensis are often put under the umbrella species name of Homo erectus.[22] Starting with Homo georgicus—found in what is now the Republic of Georgia, dated at 1.8 Ma—the pelvis and backbone grew more human-like, which would enable H. georgicus to cover very long distances and to follow herds of prey animals; this is the oldest fossil of a hominin found outside of Africa. Control of fire by early humans is achieved about 1.5 Ma by Homo ergaster. Homo ergaster reaches a height of around 1.9 metres (6.2 ft). Evolution of dark skin, which is linked to the loss of body hair in human ancestors, is complete by 1.2 Ma. Homo pekinensis first appears in Asia around 700 ka but, according to the theory of a recent African origin of modern humans, they could not be ancestors to modern humans, but rather, were an offshoot cousin species from Homo erectus. Homo heidelbergensis was a very large hominin that developed a more advanced complement of cutting tools and may have hunted big game such as horses.
1.2 Ma	Homo antecessor may be a common ancestor of humans and Neanderthals.[23][24] At present estimate, humans have approximately 20,000–25,000 genes and share 99% of their DNA with the now extinct Neanderthal [25] and 95-99% of their DNA with their closest living evolutionary relative, the chimpanzees.[26][27] The human variant of the FOXP2 gene (linked to the control of speech) has been found to be identical in Neanderthals.[28] It can therefore be deduced that Homo antecessor would also have had the human FOXP2 gene.
600 ka	A reconstruction of Homo heidelbergensis Three 1.5 m (5 ft) tall Homo heidelbergensis left footprints in powdery volcanic ash solidified in Italy. Homo heidelbergensis may be a common ancestor of humans and Neanderthals.[29] It is morphologically very similar to Homo erectus but Homo heidelbergensis had a larger brain-case, about 93% the size of that of Homo sapiens. The holotype of the species was tall, 1.8 m (6 ft) and more muscular than modern humans. Beginning of the Middle Paleolithic.
200 ka	Omo1 and Omo2 sites, (Omo River, Ethiopia), yield the earliest fossil evidence for anatomically modern Homo sapiens.[30] By a 2015 study, the hypothetical man Y-chromosomal Adam is estimated to have lived in East Africa about 250 ka. He would be the most recent common ancestor from whom all male human Y chromosomes are descended.[31]
160 ka	Homo sapiens (Homo sapiens idaltu) in Ethiopia, Awash River (near present-day Herto village) practice mortuary rituals and butcher hippopotami. Potential earliest evidence of anatomical and aspects of behavioral modernity consistent with the continuity hypothesis including use of red ochre and fishing.[32] The hypothetical woman Mitochondrial Eve is estimated to have lived in East Africa between 99 and 200 ka.
90 ka	Appearance of mitochondrial haplogroup (mt-haplogroup) L2.
60 ka	Appearance of mt-haplogroups M and N, which participated in a migration out of Africa. Homo sapiens who leave Africa in this wave may have interbred with the Neanderthals they encounter.[33][34]
50 ka	Behavioral modernity develops, according to the "great leap forward" theory.[35] Migration to South Asia. M168 mutation (carried by all non-African males). Beginning of the Upper Paleolithic. Appearance of mt-haplogroups U and K.
40 ka	Migration to Australia[36] and Europe; Cro-Magnon develops in Europe.
25 ka - 40 ka	The independent Neanderthal lineage dies out.[37] Appearance of: Y-Haplogroup R2; mt-haplogroups J and X.
10-20 ka	Beginning of the Mesolithic / Holocene. Appearance of: Y-Haplogroup R1a; mt-haplogroups V and T. Evolution of light skin in Europeans (SLC24A5).[38][39] Homo floresiensis dies out, leaving Homo sapiens as the only living species of the genus Homo.

See also

• Chimpanzee-human last common ancestor
• Dawn of Humanity (2015 PBS film)
• Homininae
• Human evolution
• Human taxonomy
• Homo
• Most recent common ancestor
• List of human evolution fossils
• March of Progress - famous illustration of 25 million years of human evolution
• Prehistoric amphibian
• Prehistoric fish
• Prehistoric reptile
• The Ancestor's Tale by Richard Dawkins - timeline comprising 40 rendezvous points
• Timeline of evolution – explains the evolution of animals living today
• Timeline of prehistory
• Y-DNA haplogroups by ethnic groups

General:

• Evolutionary history of life
• Graphical timeline of the universe
• History of Earth
• History of the world
• Natural history

References

1. "'Experiments with sex have been very hard to conduct,' Goddard said. 'In an experiment, one needs to hold all else constant, apart from the aspect of interest. This means that no higher organisms can be used, since they have to have sex to reproduce and therefore provide no asexual control.'
   Goddard and colleagues instead turned to a single-celled organism, yeast, to test the idea that sex allows populations to adapt to new conditions more rapidly than asexual populations." Sex Speeds Up Evolution, Study Finds (URL accessed on January 9, 2005)
2. Dawkins, R. (2005), The Ancestor's Tale: A Pilgrimage to the Dawn of Evolution, Houghton Mifflin Harcourt, ISBN 978-0-618-61916-0
3. "Proterospongia is a rare freshwater protist, a colonial member of the Choanoflagellata." "Proterospongia itself is not the ancestor of sponges. However, it serves as a useful model for what the ancestor of sponges and other metazoans may have been like." http://www.ucmp.berkeley.edu/protista/proterospongia.html Berkeley University
4. "Obviously vertebrates must have had ancestors living in the Cambrian, but they were assumed to be invertebrate forerunners of the true vertebrates — protochordates. Pikaia has been heavily promoted as the oldest fossil protochordate." Richard Dawkins 2004 The Ancestor's Tale Page 289, ISBN 0-618-00583-8
5. Shu, D. G.; Luo, H. L.; Conway Morris, S.; Zhang, X. L.; Hu, S. X.; Chen, L.; Han, J.; Zhu, M.; Li, Y.; Chen, L. Z. (1999). "Lower Cambrian vertebrates from south China". Nature 402 (6757): 42–46. Bibcode:1999Natur.402...42S. doi:10.1038/46965.
6. Chen, J. Y.; Huang, D. Y.; Li, C. W. (1999). "An early Cambrian craniate-like chordate". Nature 402 (6761): 518–522. Bibcode:1999Natur.402..518C. doi:10.1038/990080.
7. Shu, D. G.; Morris, S. C.; Han, J.; Zhang, Z. F.; Yasui, K.; Janvier, P.; Chen, L.; Zhang, X. L.; Liu, J. N.; Li, Y.; Liu, H. -Q. (2003), "Head and backbone of the Early Cambrian vertebrate Haikouichthys", Nature 421 (6922): 526–529, Bibcode:2003Natur.421..526S, doi:10.1038/nature01264, PMID 12556891
8. These first vertebrates lacked jaws, like the living hagfish and lampreys. Jawed vertebrates appeared 100 million years later, in the Silurian. http://www.ucmp.berkeley.edu/vertebrates/vertintro.html Berkeley University
9. "Bones of first gill arch became upper and lower jaws." (Image)
10. A fossil coelacanth jaw found in a stratum datable 410 mya that was collected near Buchan in Victoria, Australia's East Gippsland, currently holds the record for oldest coelacanth; it was given the name Eoactinistia foreyi when it was published in September 2006.
11. "Lungfish are believed to be the closest living relatives of the tetrapods, and share a number of important characteristics with them. Among these characters are tooth enamel, separation of pulmonary blood flow from body blood flow, arrangement of the skull bones, and the presence of four similarly sized limbs with the same position and structure as the four tetrapod legs." http://www.ucmp.berkeley.edu/vertebrates/sarco/dipnoi.html Berkeley University
12. "the ancestor that amphibians share with reptiles and ourselves? " " These possibly transitional fossils have been much studied, among them Acanthostega, which seems to have been wholly aquatic, and Ichthyostega" Richard Dawkins 2004 The Ancestor's Tale page 250, ISBN 0-618-00583-8
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14. "In many respects, the pelycosaurs are intermediate between the reptiles and mammals" http://www.ucmp.berkeley.edu/synapsids/pelycosaurs.html Berkeley University
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External links

• Palaeos
• Hominid Timeline
• Berkeley Evolution
• History of Animal Evolution
• Tree of Life Web Project - explore complete phylogenetic tree interactively
• Human Evolution Timeline Interactive by The Smithsonian Institution's Human Origins Program