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Timeline of human evolution



  The timeline of human evolution outlines the major events in the development of human species, and the evolution of humans' ancestors. It includes a brief explanation of some animals, species or genera, which are possible ancestors of Homo sapiens sapiens. It begins with the origin of life and presents a possible line of descendants that led to humans. This timeline is based on studies from paleontology, developmental biology, morphology and from anatomical and genetic data. The study of human evolution is a major component of anthropology.

Additional recommended knowledge

Timeline

Date Event
4000 Ma The earliest life appears.

See: Origin of life

3900 Ma Cells resembling prokaryotes appear.

See: Origins of cells

2500 Ma First organisms to utilize oxygen.
2100 Ma More complex cells appear: the eukaryotes.

See : Eukaryote Origin and Evolution

1200 Ma Sexual reproduction evolves, leading to faster evolution.[1]
900 Ma  

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] 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 The movement of all animals may have started with cnidarians. Almost all cnidarians possess nerves and muscles and, because they are the simplest animals to possess it, their direct ancestors were very likely 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.
550 Ma  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.
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 the gill-like structure it uses for breathing, a structure similar to that of primitive fish. Acorn worms are thus sometimes said to be a link between vertebrates and invertebrates.
530 Ma  

The earliest known ancestor of the chordates is Pikaia. It is the first known animal with a notochord. Pikaia is believed to be the ancestor of all chordates and vertebrates.[3]


The Lancelet, still living today, retains some characteristics of the primitive chordates. It resembles Pikaia

Other earliest known chordate-like fossils is from a conodonts a "eel-shaped animal of 4-20 cm (1½-8 in) long" with a pair of huge eyes at the head end were and a complex basket of teeth.

505 Ma  

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 the Precursors to the bony fish. [4]

480 Ma  

The Placodermi were prehistoric fishes. Placoderms were the first of the jawed fishes, their jaws evolving from the first of their gill arches [5]. Their head and thorax were covered by articulated armoured plates and the rest of the body was scaled or naked.

400 Ma First Coelacanth appears; 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.
375 Ma Tiktaalik is a genus of sarcopterygian (lobe-finned) fishes from the late Devonian with many tetrapod-like features.
365 Ma  

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. These 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.[6]

Panderichthys is a 90-130 cm (35-50 in) long fish from the Late Devonian period. It has a large tetrapod-like head. Panderichthys exhibits features transitional between lobe-finned fishes and early tetrapods.

Lungfishes retain some characteristics of the early Tetrapodas. One example is the Australian Lungfish.

315 Ma  

  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.[7]

Amphibia were the first four-legged animals to develop lungs.

Amphibians living today still retain many characteristics of the early tetrapods.

300 Ma  

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.

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 system, compared to amphibians. They have twelve pairs of cranial nerves.

256 Ma  

Shortly after the appearance of the first reptiles, two branches split off. One branch is the Diapsida from which come the modern reptiles. The other branch is Synapsida which had temporal fenestra, a pair of holes in their skulls behind the eyes, which were used to increase the space for jaw muscles.

The earliest mammal-like reptiles are the pelycosaurs. The pelycosaurs were the first animals to have temporal fenestra. Pelycosaurs are not Therapsida but soon they gave rise to them. The Therapsida are 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. [8]

220 Ma One sub-group of therapsids, the cynodonts evolved more mammal-like characteristics.

The jaws of cynodonts resemble modern mammal jaws. It is very likely this group of animals contains a species which is the direct ancestor of all modern mammals.[9]

220 Ma  

From eucynodonts (cynodonts) came the first mammals. Most early mammals were small and 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, milk glands for their young. The neocortex region of the brain first evolved in mammals and thus is unique to them.

125 Ma  

Eomaia scansoria, a eutherian mammal, leads to the formation of modern placental mammals. It looks like modern dormouse, climbing small shrubs in Liaoning, China.

100 Ma Common genetic ancestor of mice and humans.
65 Ma  

  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 proto-primate Plesiadapiformes. One of the early proto-primates is Plesiadapis. Plesiadapis still had claws and the eyes located on each side of the head, because of that they were faster on the ground than on the top of the trees, but they begin 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.[10]

One of the last Plesiadapiformes is Carpolestes simpsoni. It had grasping digits but no forward facing eyes.

40 Ma Primates diverge into suborders Strepsirrhini (wet-nosed primates) and Haplorrhini (dry nosed primates). Strepsirrhini contains most of the prosimians; modern examples include the lemurs and lorises. The haplorrhines include the three living groups the prosimian tarsiers, the simian monkeys, and apes. One of the earliest haplorrhines is Teilhardina asiatica, a mouse-sized, diurnal creature with small eyes.
30 Ma  

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 Atlantic ocean (circa 4,500 km, 2,800 mi). Catarrhines mostly stayed in Africa as the two continents drifted apart. One ancestor of catarrhines might be Aegyptopithecus.

25 Ma  

Catarrhini splits into 2 superfamilies, Old World monkeys (Cercopithecoidea) and apes (Hominoidea).

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, and humans.

15 Ma Human ancestors speciate from the ancestors of the gibbon (lesser apes).
13 Ma Human ancestors speciate from the ancestors the orangutan[11].

Pierolapithecus catalaunicus is believed to be a common ancestor of humans and the great apes or at least a species that brings us closer to a common ancestor than any previous fossil discovery.

Pierolapithecus had special adaptations for tree climbing, just as humans and other great apes do: a wide, flat ribcage, a stiff lower spine, flexible wrists, and shoulder blades that lie along its back.

10 Ma Human ancestors speciate from the ancestors of the gorillas.
5 Ma  

Human ancestors speciate from the ancestors of the chimpanzees. The latest common ancestor is Sahelanthropus tchadensis. The earliest in the human branch is Orrorin tugenensis (Millennium Man, Kenya). 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 precursor of speech.

4.4 Ma Ardipithecus ramidus ramidus
3.7 Ma Some Australopithecus afarensis left footprints on volcanic ash in Laetoli, Kenya (Northern Tanzania).
3 Ma The bipedal australopithecines (early hominines) evolve in the savannas of Africa being hunted by Dinofelis.
2 Ma  

Homo habilis is thought to be the ancestor of the lankier and more sophisticated, Homo ergaster. Lived side by side the Homo erectus until at least 1.44 Ma, making it highly unlikey that Homo erectus directly evolved out of Homo habilis. First stone tools, beginning of the Lower Paleolithic. see: Homo rudolfensis

1.8 Ma  

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 and the teeth are smaller.

It is believed to be an ancestor of modern humans (with Homo heidelbergensis usually treated as an intermediary step).

1.75 Ma Dmanisi man / Homo georgicus (Georgia, Russia), tiny brain came from Africa, with Homo erectus and Homo habilis characteristics. Homo erectus migrates out of Africa and colonizes Eurasia. Control of fire by early humans.
700 ka Common genetic ancestor of humans and Neanderthal, though the accuracy of this finding has been questioned.[12] At present estimate, humans have approximately 20,000–25,000 genes and share 99% of their DNA with the now extinct Neanderthal [13] and 95% of their DNA with their closest living evolutionary relative, the chimpanzees[14].
355 ka  

Three 1.5 m (5 ft) tall Homo heidelbergensis left footprints in powdery volcanic ash solidified in Italy. Homo heidelbergensis is the common ancestor of both Homo neanderthalensis and Homo sapiens. 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 species was tall, 1.8 m (6 ft) on average, and more muscular than modern humans. Beginning of the Middle Paleolithic.

195 ka Omo1, Omo2 (Ethiopia, Omo river) are the earliest fossil evidence for archaic Homo sapiens, evolved from Homo heidelbergensis.
160 ka Homo sapiens (Homo sapiens idaltu) in Ethiopia, Awash River, Herto village, practise mortuary rituals and butcher hippos.
150 ka  

Mitochondrial Eve lives in East Africa. She is the most recent female ancestor common to all mitochondrial lineages in humans alive today.

70 ka appearance of mitochondrial haplogroup L2. Behavioral modernity. The FOXP2 gene (associated with the development of speech) appears in this period.[15]
60 ka Y-chromosomal Adam lives in Africa. He is the most recent common ancestor from whom all male human Y chromosomes are descended. Appearance of mitochondrial haplogroups M and N, which participate in the migration out of Africa.
50 ka Migration to South Asia. M168 mutation (carried by all non-African males). Beginning of the Upper Paleolithic. mt-haplogroups U, K.
40 ka Migration to Australia and Europe (Cro-Magnon).
25 ka Neanderthals die out, leaving Homo sapiens as the only living species of the genus Homo. Y-Haplogroup R2; mt-haplogroups J, X.
12 ka Beginning of the Mesolithic / Holocene. Y-Haplogroup R1a; mt-haplogroup V, T.

See also

  • Graphical timeline of our universe
  • History of Earth
  • Natural history
  • History of the world
  • Evolutionary history of life
  • Human evolution
  • Homo (genus)
  • Most recent common ancestor
  • List of human fossils
  • Prehistoric amphibian
  • Prehistoric fish
  • Prehistoric mammal
  • Prehistoric reptile
  • The Ancestor's Tale by Richard Dawkins with a timeline comprising 40 rendezvous points
  • Timeline of evolution - an explanation of the evolution of a wide variety of animals living today

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. ^ "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
  3. ^ "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 0618005838
  4. ^ 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
  5. ^ "Bones of first gill arch became upper and lower jaws." (Image) (URL accessed on November 16, 2006)
  6. ^ "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
  7. ^ "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 0618005838
  8. ^ "In many respects, the pelycosaurs are intermediate between the reptiles and mammals" http://www.ucmp.berkeley.edu/synapsids/pelycosaurs.html Berkeley University
  9. ^ "Tlvinaxodon, like any fossil, should be thought of as a cousin of our ancestor, not the ancestor itself. It was a member of a group of mammal-like reptiles called the cynodonts. The cynodonts were so mammal-like, it is tempting to call them mammals. But who cares what we call them? They are almost perfect intermediates." Richard Dawkins 2004 The Ancestor's Tale page 211, ISBN 0618005838
  10. ^ "Fossils that might help us reconstruct what Concestor 8 was like include the large group called plesiadapi-forms. They lived about the right time, and they have many of the qualities you would expect of the grand ancestor of all the primates" Richard Dawkins 2004 The Ancestor's Tale page 136, ISBN 0618005838
  11. ^ Raauma, Ryan, Sternera, K., (2005) "Catarrhine primate divergence dates estimated from complete mitochondrial genomes", Journal of Human Evolution 48: 237-257 [1]
  12. ^ C. David Kreger. Homo Neanderthalensis
  13. ^ "Rubin also said analysis so far suggests human and Neanderthal DNA are some 99.5 percent to nearly 99.9 percent identical." Neanderthal bone gives DNA clues (URL accessed on November 16, 2006)
  14. ^ "The conclusion is the old saw that we share 98.5% of our DNA sequence with chimpanzee is probably in error. For this sample, a better estimate would be that 95% of the base pairs are exactly shared between chimpanzee and human DNA." Britten, R.J. (2002). "Divergence between samples of chimpanzee and human DNA sequences is 5%, counting indels". PNAS. doi:10.1073/pnas.172510699.
  15. ^ Attempts to date the age of the gene have attracted controversy; e.g. Karl C. Diller and Rebecca L. Cann (2007). "Evidence against a genetic-based revolution in language 50,000 years ago". Retrieved on 2007-12-22.


 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Timeline_of_human_evolution". A list of authors is available in Wikipedia.
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