Timeline of human evolution

Choanoflagellate

The choanoflagellates may look similar to the ancestors of the entire animal kingdom, and in particular they may be the ancestors of sponges.[5][6]

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.

Dickinsonia costata from the Ediacaran biota, 635–542 Ma, a possible early member of Animalia.

Urmetazoan: The first fossils that might represent animals appear in the 665-million-year-old rocks of the Trezona Formation of South Australia. These fossils are interpreted as being early sponges.[7] Separation from the Porifera (sponges) lineage. Eumetazoa/Diploblast: separation from the Ctenophora ("comb jellies") lineage. Planulozoa/ParaHoxozoa: separation from the Placozoa and Cnidaria lineages. Almost all cnidarians possess nerves and muscles. Because they are the simplest animals to possess them, their 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.

Proporus sp., a xenacoelomorph.

Urbilaterian: Bilateria/Triploblasts, Nephrozoa (555 Ma), last common ancestor of protostomes (including the arthropod [insect, crustacean] and platyzoan [flatworms] lineages) and the deuterostomes (including the vertebrate [human] lineage). Earliest development of the brain, and of bilateral symmetry. Archaic representatives of this stage are flatworms, the simplest animals with organs that form from three germ layers.

A sea cucumber (Actinopyga echinites), displaying its feeding tentacles and tube feet.

Most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion. Deuterostomes, last common ancestor of the chordate [human] lineage, the Echinodermata (starfish, sea urchins, sea cucumbers, etc.) and Hemichordata (acorn worms and graptolites).

An archaic survivor from this stage is the acorn worm, sporting 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 have a plexus concentrated into both dorsal and ventral nerve cords. The dorsal cord reaches into the proboscis, and is partially separated from the epidermis in that region. This part of the dorsal nerve cord is often hollow, and may well be homologous with the brain of vertebrates.[8]

Pikaia

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

Conodont

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).[13]

A placoderm

The Placodermi were prehistoric fishes. Placoderms were some of the first jawed fishes (Gnathostomata), their jaws evolving from the first gill arch.[14] 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 descendants after the end of the Devonian and are less closely related to living bony fishes than sharks are.

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.[16]

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.

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.

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 were not 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.[17]

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.

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. It is used in the claws of modern lizards and birds, and hair in mammals.[18]

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 inhabit the uplands for the first time.

Reptiles have advanced nervous systems, compared to amphibians, with twelve pairs of cranial nerves.

Phthinosuchus, an early Therapsid

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 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.[19]

Cynognathus

One subgroup of therapsids, the cynodonts, evolved more mammal-like characteristics.

The jaws of cynodonts resemble modern mammal jaws. This group of animals likely contains a species which is the ancestor of all modern mammals.[20]

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 sexual differentiation through the existence or lack of SRY gene (found in the y-Chromosome) evolved after the monotreme lineage split off.

Juramaia sinensis

Juramaia sinensis[21] is the earliest known eutherian mammal fossil.

Plesiadapis

Carpolestes simpsoni

A group of small, nocturnal, arboreal, insect-eating mammals called Euarchonta begins a speciation that will lead to the orders of primates, treeshrews and flying lemurs. Primatomorpha is a subdivision of Euarchonta including primates and their ancestral stem-primates Plesiadapiformes. An early stem-primate, Plesiadapis, still had claws and eyes on the side of the head, making it faster on the ground than in the trees, but it began to spend long times on lower branches, feeding on fruits and leaves.

The Plesiadapiformes very likely contain the ancestor species of all primates.[22] They first appeared in the fossil record around 66 million years ago, soon after the Cretaceous–Paleogene extinction event that eliminated about three-quarters of plant and animal species on Earth, including most dinosaurs.[23][24]

One of the last Plesiadapiformes is Carpolestes simpsoni, having grasping digits but not forward-facing eyes.

Aegyptopithecus

Haplorrhini splits into infraorders Platyrrhini and Catarrhini. Platyrrhines, New World monkeys, have prehensile tails and males are color blind. The individuals whose descendants would become Platyrrhini are conjectured to have migrated to South America either on a raft of vegetation or via a land bridge (the hypothesis now favored[25]). Catarrhines mostly stayed in Africa as the two continents drifted apart. Possible early ancestors of catarrhines include Aegyptopithecus and Saadanius.

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.

Pierolapithecus catalaunicus is thought 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.

Sahelanthropus tchadensis

Hominini: The latest common ancestor of humans and chimpanzees is estimated to have lived between roughly 10 to 5 million years ago. 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. Speciation may have begun shortly after 10 Ma, but late admixture between the lineages may have taken place until after 5 Ma. Candidates of Hominina or Homininae species which lived in this time period include Ouranopithecus (c. 8 Ma), Graecopithecus (c. 7 Ma), Sahelanthropus tchadensis (c. 7 Ma), Orrorin tugenensis (c. 6 Ma).

Ardipithecus

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.

A member of the Australopithecus afarensis left human-like footprints on volcanic ash in Laetoli, 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 (anterior-projecting) face.

Australopithecines have been found in savannah environments; they probably developed their diet to include scavenged meat. Analyses of Australopithecus africanus lower vertebrae suggests that these bones changed in females to support bipedalism even during pregnancy.

Early Homo appears in East Africa, speciating from australopithecine ancestors. Sophisticated stone tools mark the beginning of the Lower Paleolithic. Australopithecus garhi was using stone tools at about 2.5 Ma. Homo habilis is the oldest species given the designation Homo, by Leakey et al. (1964). H. habilis is intermediate between Australopithecus afarensis and H. erectus, and there have been suggestions to re-classify it within genus Australopithecus, as Australopithecus habilis.

Stone tools found at the Shangchen site in China and dated to 2.12 million years ago are considered the earliest known evidence of hominins outside Africa, surpassing Dmanisi in Georgia by 300,000 years.[34]

Homo erectus derives from early Homo or late Australopithecus.

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 H. erectus for almost half a million years (until about 1.5 Ma). From its earliest appearance at about 1.9 Ma, H. erectus is distributed in East Africa and Southwest Asia (Homo georgicus). H. erectus is the first known species to develop control of fire, by about 1.5 Ma.

H. erectus later migrates throughout Eurasia, reaching Southeast Asia by 0.7 Ma. It is described in a number of subspecies.[35]

Evolution of dark skin at about 1.2 Ma.[36]

Homo antecessor may be a common ancestor of humans and Neanderthals.[37][38] At present estimate, humans have approximately 20,000–25,000 genes and share 99% of their DNA with the now extinct Neanderthal [39] and 95–99% of their DNA with their closest living evolutionary relative, the chimpanzees.[40][41] The human variant of the FOXP2 gene (linked to the control of speech) has been found to be identical in Neanderthals.[42]

Divergence of Neanderthal and Denisovan lineages from a common ancestor.[43] Homo heidelbergensis (in Africa also known as Homo rhodesiensis) had long been thought to be a likely candidate for the last common ancestor of the Neanderthal and modern human lineages. However, genetic evidence from the Sima de los Huesos fossils published in 2016 seems to suggest that H. heidelbergensis in its entirety should be included in the Neanderthal lineage, as "pre-Neanderthal" or "early Neanderthal", while the divergence time between the Neanderthal and modern lineages has been pushed back to before the emergence of H. heidelbergensis, to about 600,000 to 800,000 years ago, the approximate age of Homo antecessor.[44][45]

Solidified footprints dated to about 350 ka and associated with H. heidelbergensis were found in southern Italy in 2003.[46]

Reconstruction of H. neanderthalensis

Fossils attributed to H. sapiens, along with stone tools, dated to approximately 300,000 years ago, found at Jebel Irhoud, Morocco[47] yield the earliest fossil evidence for anatomically modern Homo sapiens. Modern human presence in East Africa (Gademotta), at 276 kya.[48] A 177,000-year-old jawbone fossil discovered in Israel in 2017 is the oldest human remains found outside Africa.[49] However, in July 2019, anthropologists reported the discovery of 210,000 year old remains of a H. sapiens and 170,000 year old remains of a H. neanderthalensis in Apidima Cave, Peloponnese, Greece, more than 150,000 years older than previous H. sapiens finds in Europe.[50][51][52]

Neanderthals emerge from the Homo heidelbergensis lineage at about the same time (300 ka).

Patrilineal and matrilineal most recent common ancestors (MRCAs) of living humans roughly between 200 and 100 ka[53][54] with some estimates on the patrilineal MRCA somewhat higher, ranging up to 250 to 500 kya.[55]

160,000 years ago, Homo sapiens idaltu in the Awash River Valley (near present-day Herto village, Ethiopia) practiced excarnation.[56]

Modern human presence in Southern Africa and West Africa.[57] Appearance of mitochondrial haplogroup (mt-haplogroup) L2.

Early evidence for behavioral modernity.[58] Appearance of mt-haplogroups M and N. Southern Dispersal migration out of Africa, Proto-Australoid peopling of Oceania.[59] Archaic admixture from Neanderthals in Eurasia,[60][61] from Denisovans in Oceania with trace amounts in Eastern Eurasia,[62] and from an unspecified African lineage of archaic humans in Sub-Saharan Africa as well as an interbred species of Neanderthals and Denisovans in Asia and Oceania.[63][64][65][66]

Reconstruction of Oase 2 (c. 40 ka)

Behavioral modernity develops, according to the "great leap forward" theory.[67] Extinction of Homo floresiensis.[68] M168 mutation (carried by all non-African males). Appearance of mt-haplogroups U and K. Peopling of Europe, peopling of the North Asian Mammoth steppe. Paleolithic art. Extinction of Neanderthals and other archaic human variants (with possible survival of hybrid populations in Asia and Africa.) Appearance of Y-Haplogroup R2; mt-haplogroups J and X.

Last Glacial Maximum; Epipaleolithic / Mesolithic / Holocene. Peopling of the Americas. Appearance of: Y-Haplogroup R1a; mt-haplogroups V and T. Various recent divergence associated with environmental pressures, e.g. light skin in Europeans and East Asians (KITLG, ASIP), after 30 ka;[69] Inuit adaptation to high-fat diet and cold climate, 20 ka.[70]

Extinction of late surviving archaic humans at the beginning of the Holocene (12 ka). Accelerated divergence due to selection pressures in populations participating in the Neolithic Revolution after 12 ka, e.g. East Asian types of ADH1B associated with rice domestication,[71] or lactase persistence.[72][73]