Chapter 22.2

Skeleton and Reconstruction of Turkana Boy

Like modern humans, H. erectus varied widely in size, ranging from 146–185 cm (4 ft 9 in – 6 ft 1 in) in height and 40–68 kg (88–150 lb) in weight, thought to be due to regional differences in climate, mortality rates, or nutrition. Among primates, this marked of a response to environmental stressors (phenotypic plasticity) is only demonstrated in modern humans.

Like modern humans and unlike other great apes, there does not seem to have been a great size disparity between H. erectus men and women (size-specific sexual dimorphism), though there is not much fossil data regarding this. Brain size in two adults from Koobi Fora measured 848 and 804 cc (51.7 and 49.1 cu in) and another significantly smaller adult measured 691 cubic cetimeters (42.2 cu in), which could possibly indicate sexual dimorphism, though sex was undetermined. Another case that depicts the difficulty of assigning sex to the fossil record is a few samples taken in Olduvai Gorge. In Olduvai Gorge two skulls identified as OH12 and OH9, were found to be that of H. erectus with a cranial capacities of 1000 cubic centimeters and 700 cubic centimeters. It is unclear if sexual dimorphism is at play here since the remains

are fragmentary. If H. erectus did not exhibit sexual dimorphism, then it is possible that they were the first in the human line to do so, though the fragmentary fossil record for earlier species makes this unclear. If yes, then there was a substantial and sudden increase in female height. Certain features of sexual dimorphism are often identified in the possibility of determining sex such as lack of muscle marking.

Reconstruction of a Female Homo Erectus

Homo erectus had about the same limb configurations and proportions as modern humans, implying humanlike locomotion, the first in the Homo lineage. H. erectus tracks near Ileret, Kenya, also indicate a human gait. A humanlike shoulder suggests an ability for high speed throwing. It was once thought that Turkana boy had 6 lumbar vertebra instead of the 5 seen in modern humans and 11 instead of 12 thoracic vertebrae, but this has since been revised, and the specimen is now considered to have exhibited a humanlike curvature of the spine (lordosis) and the same number of respective vertebrae.

It is largely unclear when human ancestors lost most of their body hair. Genetic analysis suggests that high activity in the melanocortin 1 receptor, which would produce dark skin, dates back to 1.2 million years ago. This could indicate the evolution of hairlessness around this time, as a lack of body hair would have left the skin exposed to harmful UV radiation. It is possible that exposed skin only became maladaptive in the Pleistocene, because the increasing tilt of the Earth (which also caused the ice ages) would have increased solar radiation bombardment- which would suggest that hairlessness first emerged in the australopithecines. However, australopithecines seem to have lived at much higher, much colder elevations—typically 1,000–1,600 m (3,300–5,200 ft) where the nighttime temperature can drop to 10 or 5 °C (50 or 41 °F)—so they may have required hair to stay warm, unlike early Homo which inhabited lower, hotter elevations. Populations in higher latitudes potentially developed lighter skin to prevent vitamin D deficiency. A 500–300 thousand years ago H. erectus specimen from Turkey was diagnosed with the earliest known case of tuberculous meningitis, which is typically exacerbated in dark-skinned people living in higher latitudes due to vitamin D deficiency. Hairlessness is generally thought to have facilitated sweating, but reduction of parasite load and sexual selection have also been proposed.

The 1.8 million years ago Mojokerto child specimen from Java, who died at about 1 year of age, presented 72–84 percent of the average adult brain size, which is more similar to the faster brain growth trajectory of great apes than modern humans. This indicates that H. erectus was probably not cognitively comparable to modern humans, and that secondary altriciality—an extended childhood and long period of dependency due to the great amount of time required for brain maturation—evolved much later in human evolution, perhaps in the modern human/Neanderthal last common ancestor. It was previously believed that, based on the narrow pelvis of Turkana boy, H. erectus could only safely deliver a baby with a brain volume of about 230 cubic centimeters (14 cu in), equating to a similar brain growth rate as modern humans to achieve the average adult brain size of 600–1,067 cubic centimeters (36.6–65.1 cu in). However, a 1.8 Ma female pelvis from Gona, Ethiopia, shows that H. erectus babies with a brain volume of 310 cubic centimeters (19 cu in) could have been safely delivered, which is 34–36 percent the mean adult size, compared to 40 percent in chimps and 28 percent in modern humans. This more aligns with the conclusions drawn from the Mojokerto child. A faster development rate could indicate a lower expected lifespan.

Based on an average mass of 63 kg (139 lb) for males and 52.3 kg (115 lb) for females, the total energy expenditure (TEE)—the amount of calories consumed in one day—was estimated to be about 2271.8 and 1909.5 kcal, respectively. This is similar to that of earlier Homo, despite a marked increase in activity and migratory capacity, likely because the longer legs of H. erectus were more energy-efficient in long-distance movement. Nonetheless, the estimate for H. erectus females is 84 percent higher than that for Australopithecus females, possibly due to an increased body size and a decreased growth rate. A study, assuming high energy or dietary fat requirements based on the abundance of large game animals at H. erectus sites, calculated a TEE of 2,700–3,400 kcal of which 27–44% derived from fat, and 44–62% of the fat from animal sources. In comparison, modern humans with a similar activity level have a DEE of 2,450 calories, of which 33% derives from fat, and 49% of the fat from animals.

Cross sections of Chinese H. erectus humeri (upper arm bones) showing extremely thickened cortical bone. The cortical bone (the outer layer of the bone) is extraordinarily thickened, particularly in East Asian populations. The skull caps have oftentimes been confused with fossil turtle carapaces, and the medullary canal in the long bones (where the bone marrow is stored, in the limbs) is extremely narrowed (medullary stenosis). This degree of thickening is usually exhibited in semi-aquatic animals which used their heavy (pachyosteosclerotic) bones as ballasts to help them sink, induced by hypothyroidism. Male specimens have thicker cortical bone than females.

It is largely unclear what function this could have served. All pathological inducers would leave scarring or some other indicator not normally exhibited in H. erectus. Before more complete skeletons were discovered, H. erectus was a gigantic species, thickened bone required to support the massive weight. It was hypothesized that intense physical activity could have induced bone thickening, a low correlation between the two at least in modern humans. Different races have different average cortical bone thicknesses, and concluded it is genetic rather than environmental. It is unclear if the condition is caused by increased bone apposition (bone formation) or decreased bone resorption, but it was noted that the stenosis is quite similar to the congenital condition in modern humans induced by hyper-apposition.

Supra orbital torus is a response to withstanding major bending stress which localizes in that region when significant force is applied through the front teeth, such as while using the mouth as a third hand to carry objects. It was a result of a cultural practice, wherein H. erectus would fight each other with fists, stones, or clubs to settle disputes or battle for mates, since the skull is reinforced in key areas. The mandible is quite robust, capable of absorbing heavy blows (no "glass jaw"); the heavy brow ridge protects the eyes, and transitions into a bar covering the ears, connecting all the way in the back of the skull, meaning blows to any of these regions can be effectively dissipated across the skull; and the sagittal keel protects the top of the brain case. Many skull caps bear usually debilitating fractures, such as the Peking Man skull, yet they can show signs of surviving and healing. Anthropologists suggested a similar reason for the unusual thickening of the modern Australian Aboriginal skull, a result of a ritual popular in central and southeast Australian tribes where adversaries would wack each other with waddies (sticks) until knockout.

The only fossil evidence regarding H. erectus group composition comes from 4 sites outside of Ileret, Kenya, where 97 footprints made 1.5 million years ago were likely left by a group of at least 20 individuals. One of these track ways, based on the size of the footprints, may have been an entirely male group, which could indicate they were some specialized task group, such as a hunting or foraging party, or a border patrol. If correct, this would also indicate sexual division of labor, which distinguishes human societies from those of other great apes and social mammalian carnivores. In modern hunter gatherer societies who target large prey items, typically male parties are dispatched to bring down these high-risk animals, and, due to the low success rate, female parties focus on more predictable foods. Based on modern day savanna chimp and baboon group composition and behavior, H. erectus ergaster may have lived in large, multi-male groups in order to defend against large savanna predators in the open and exposed environment. However, dispersal patterns indicate that H. erectus generally avoided areas with high carnivore density. It is possible that male–male bonding and male–female friendships were important societal aspects.

The H. erectus children had faster brain growth rates, it likely did not exhibit the same degree of maternal investment or child-rearing behaviors as modern humans it's because H. erectus men and women are thought to have been about the same size compared to other great apes (exhibit less size-specific sexual dimorphism), it is generally hypothesized that they lived in a monogamous society, as reduced sexual dimorphism in primates is typically correlated with this mating system. However, it is unclear if H. erectus did in fact exhibit humanlike rates of sexual dimorphism. If they did, then it would mean only female height increased from the ancestor species, which could have been caused by a shift in female fertility or diet, and/or reduced pressure on males for large size. This in turn could imply a shift in female behavior which made it difficult for males to maintain a harem.

Increasing brain size is often directly associated with a meatier diet and resultant higher caloric intake. An increase in insect protein consumption, Entomophagy, has also been proposed as a possible cause. However, it is also possible that the energy-expensive guts decreased in size in H. erectus, because the large ape gut is used to synthesize fat by fermenting plant matter which was replaced by dietary animal fat, allowing more energy to be diverted to brain growth. This would have increased brain size indirectly while maintaining the same caloric requirements of ancestor species. H. erectus may have also been the first to use a hunting and gathering food collecting strategy as a response to the increasing dependence on meat. With an emphasis on teamwork, division of labor, and food sharing, hunting and gathering was a dramatically different subsistence strategy from previous modes.

Homo erectus diet likely varied widely depending upon location. For example, at the 780 ka Gesher Benot Ya'aqov site, Israel, the inhabitants gathered and ate 55 different types of fruits, vegetables, seeds, nuts, and tubers, and it appears that they used fire to roast certain plant materials that otherwise would have been inedible; they also consumed amphibians, reptiles, birds, aquatic and terrestrial invertebrates, in addition to the usual large creatures such as elephant

and fallow deer. At the lakeside site in the East Turkana Basin, Kenya, the inhabitants ate (alongside the usual bovids, hippos, and rhinos) aquatic creatures such as turtles, crocodiles, and catfish. The large animals were likely scavenged at this site, but the turtles and fish were possibly collected live. At Trinil H. K. site, Java, H. erectus likely gathered fish and shellfish.

Dentally, H. erectus mouths were not as versatile as those of ancestor species, capable of processing a narrower range of foods. However, tools were likely used to process hard foods, thus affecting the chewing apparatus, and this combination may have instead increased dietary flexibility (though this does not equate to a highly varied diet). Such versatility may have permitted H. erectus to inhabit a range of different environments, and migrate beyond Africa.

Some anthropologists proposed the "cooking hypothesis" which states that H. erectus speciated from the ancestral H. habilis because of fire usage and cooking 2 Million years ago to explain the rapid doubling of brain size between these two species in only a 500,000 year timespan, and the sudden appearance of the typical human body plan. Cooking makes protein more easily digestible, speeds up nutrient absorption, and destroys food-borne pathogens, which would have increased the environment's natural carrying capacity, allowing group size to expand, causing selective pressure for sociality, requiring greater brain function. However, the fossil record does not associate the emergence of H. erectus with fire usage nor with any technological breakthrough for that matter, and cooking likely did not become a common practice until after 400 thousand years ago. Java Man's dispersal through Southeast Asia coincides with the extirpation of the giant turtle Megalochelys, possibly due to overhunting as the turtle would have been an easy, slow-moving target which could have been stored for quite some time.

Technology

Homo erectus is credited with inventing the Acheulean stone tool industry, succeeding the Oldowan industry, and were the first to make lithic flakes bigger than 10 cm (3.9 in), and hand axes (which includes bifacial tools with only 2 sides, such as picks, knives, and cleavers). Though larger and heavier, these hand axes had sharper, chiseled edges. They were likely multi-purpose tools, used in variety of activities such as cutting meat, wood, or edible plants. Paleontologists stated that Acheulean technology required operational intelligence (foresight and planning), being markedly more complex than Oldowan technology which included lithics of unstandardized shape, cross-sections, and symmetry. Based on this, they concluded that there is not a significant disparity in intelligence between H. erectus and modern humans and that, for the last 300,000 years, increasing intelligence has not been a major influencer of cultural evolution. However, a 1 year old H. erectus specimen shows that this species lacked an extended childhood required for greater brain development, indicating lower cognitive capabilities. A few sites, likely due to occupation over several generations, features hand axes en masse, such as at Melka Kunture, Ethiopia, Kenya and Zambia.

The earliest record of Acheulean technology comes from West Turkana, Kenya 1.76 million years ago. Oldowan lithics are also known from the site, and the two seemed to coexist for some time. The earliest records of Acheulean technology outside of Africa date to no older than one million years ago, indicating it only became widespread after some secondary H. erectus dispersal from Africa.

On Java, H. erectus produced tools from shells at Sangiran and Trinil. Spherical stones, measuring 6–12 cm (2.4–4.7 in) in diameter, are frequently found in African and Chinese Lower Paleolithic sites, and were potentially used as bolas; if correct, this would indicate string and cordage technology.

Control of Fire by Early Humans

Homo erectus is credited as the first human ancestor to have used fire, though the timing of this invention is debated mainly because campfires very rarely and very poorly preserve over long periods of time, let alone thousands or millions of years. The earliest claimed fire sites are in Kenya, The first fire keepers are thought to have simply transported to caves and maintained naturally occurring fires for extended periods of time or only sporadically when the opportunity arose. Maintaining fires would require fire keepers to have knowledge on slow-burning materials such as dung. Fire becomes markedly more abundant in the wider archaeological record after 400,000–300,000 years ago, which can be explained as some advancement in fire management techniques took place at this time or human ancestors only opportunistically used fire until this time. It is possible that fire starting was invented and lost and reinvented multiple times and independently by different communities rather than being invented in one place and spreading throughout the world. The earliest evidence of hearths comes from Gesher Benot Ya'aqov, Israel, over 700,000 years ago, where fire is recorded in multiple layers in an area close to water, both uncharacteristic of natural fires.

Artificial lighting may have led to increased waking hours—modern humans have about a 16-hour waking period, whereas other apes are generally awake from only sun up to sun down and these additional hours were probably used for socializing. Because of this, fire usage is probably also linked to the origin of language. Artificial lighting may have also made sleeping on the ground instead of the trees possible by keeping terrestrial predators at bay.

Migration into the frigid climate of Ice Age Europe may have only been possible because of fire, but evidence of fire usage in Europe until about 400–300,000 years ago is notably absent. If these early European H. erectus did not have fire, it is largely unclear how they stayed warm, avoided predators, and prepared animal fat and meat for consumption; and lightning is less common farther north equating to a reduced availability of naturally occurring fires. It is possible that they only knew how to maintain fires in certain settings in the landscapes and prepared food some distance away from home, meaning evidence of fire and evidence of hominin activity are spaced far apart. Alternatively, H. erectus may have only pushed farther north during warmer interglacial periods—thus not requiring fire, food storage, or clothing technology and their dispersal patterns indicate they generally stayed in warmer lower-to-middle latitudes. It is debated if the H. e. pekinensis inhabitants of Zhoukoudian, Northern China, were capable of controlling fires as early as 770 thousand years ago to stay warm in what may have been a relatively cold climate.

In 1962, a 366 cm × 427 cm × 30 cm (12 ft × 14 ft × 1 ft) circle made with volcanic rocks was discovered in Olduvai Gorge. At 61–76 cm (2–2.5 ft) intervals, rocks were piled up to 15–23 cm (6–9 in) high. Palaeoanthropologists suggested the rock piles were used to support poles stuck into the ground, possibly to support a windbreak or a rough hut. Some modern day nomadic tribes build similar low-lying rock walls to build temporary shelters upon, bending upright branches as poles and using grasses or animal hide as a screen. Dating to 1.75 million years ago, it is the oldest claimed evidence of architecture.

In Europe, evidence of constructed dwelling structures dating to or following the Holstein Interglacial which began 424 thousand years ago. This dwelling's base measured about 3 m × 4 m (9.8 ft × 13.1 ft) on the exterior and 3 m × 2 m (9.8 ft × 6.6 ft) on the interior, and is considered to have been a firm surface hut, probably with a vaulted roof made of thick branches or thin poles, supported by a foundation of big rocks and earth, and likely functioned as a winter base camp.

The earliest evidence of cave habitation is Wonderwerk Cave, South Africa, about 1.6 million years ago, but evidence of cave use globally is sporadic until about 600 thousand years ago.

Human taxonomy is the classification of the human species (systematic name Homo sapiens, Latin: "wise man") within zoological taxonomy. The systematic genus, Homo, is designed to include both anatomically modern humans and extinct varieties of archaic humans. Current humans have been designated as subspecies Homo sapiens sapiens, differentiated, according to some, from the direct ancestor, Homo sapiens idaltu (with some other research instead classifying idaltu and current humans as belonging to the same subspecies).

Since the introduction of systematic names in the 18th century, knowledge of human evolution has increased drastically, and a number of intermediate taxa have been proposed in the 20th and early 21st centuries. The most widely accepted taxonomy grouping takes the genus Homo as originating between two and three million years ago, divided into at least two species, archaic Homo erectus and modern Homo sapiens, with about a dozen further suggestions for species without universal recognition.

The two genera are estimated to have diverged over an extended time of hybridization spanning roughly 10 to 6 million years ago, with possible admixture as late as 4 million years ago. A sub-tribe of uncertain validity, grouping archaic "pre-human" or "para-human" species younger than the Homo-Pan split, is Australopithecina.

Hominina is a sub-tribe alongside Australopithecina, with Homo the only known genus within Hominina. Alternatively, following the "pre-

human" or "proto-human" genera of Aiustralopithecus, Ardipithecus, Praeanthropus and possibly Sahelanthropus, may be placed on equal footing alongside the genus Homo. An even more radical view rejects the division of Pan and Homo as separate genera, which based on the Principle of Priority would imply the reclassification of chimpanzees as Homo paniscus (or similar).

Categorizing humans based on phenotypes is a socially controversial subject. New World Central Hub biologists originally classified races as sub-species, but contemporary anthropologists reject the concept of race as a useful tool to understanding humanity, and instead view humanity as a complex, interrelated genetic continuum. Taxonomy of the hominins continues to evolve.

Clothing

It is largely unclear when clothing was invented, with the earliest estimate stretching as far back as 3 million years ago to compensate for a lack of insulating body hair. It is known that head lice and body lice (the latter can only inhabit clothed individuals) for modern humans diverged about 170 thousand year ago, well before modern humans left Africa, meaning clothes were already well in use before encountering cold climates. One of the first uses of animal hide is thought to have been for clothing, and the oldest hide scrapers date to about 780 thousand years ago, though this is not indicative of clothing.

Seafaring

Acheulean artifacts discovered on isolated islands that were never connected to land in the Pleistocene may show seafaring by H. erectus as early as 1 million years ago in Indonesia. They had arrived on the islands of Flores, Timor, and Roti, which would have necessitated crossing the Lombok Strait (the Wallace Line), at least before 800 thousand years ago. It is also possible they were the first European mariners as well and crossed the Strait of Gibraltar between North Africa and Spain. A genetic analysis of these island populations of H. erectus found no evidence of interbreeding with modern humans. Seafaring capability would show H. erectus had a great capacity for planning, likely months in advance of the trip.

Similarly, Homo luzonensis is dated between 771,000 to 631,000 years ago. Because Luzon has always been an island in the Quaternary, the ancestors of H. luzonensis would have had to have made a substantial sea crossing and crossed the Huxley Line.

Healthcare

The earliest probable example of infirming sick group members is a 1.77 million years H. e. georgicus specimen who had lost all but one tooth due to age or gum disease, the earliest example of severe chewing impairment, yet still survived for several years afterwards. However, it is possible australopithecines were capable of caring for debilitated group members. Unable to chew, this H. e. georgicus individual probably ate soft plant or animal foods possibly with assistance from other group members. High-latitude groups are thought to have been predominantly carnivorous, eating soft tissue such as bone marrow or brains, which may have increased survival rates for toothless individuals.

The Turkana boy was diagnosed with juvenile spinal disc herniation, and, because this specimen was still growing, this caused some scoliosis (abnormal curving of the spine).These usually cause recurrent lower back pain and sciatica (pain running down the leg), and likely restricted Turkana boy in walking, bending, and other daily activities. The specimen appears to have survived into adolescence, which evidences advanced group care.

The 1,000–700 thousnd years ago Java man specimen presents a noticeable osteocyte on the femur, likely Paget's disease of bone, and osteopetrosis, thickening of the bone, likely resulting from skeletal fluorosis caused by ingestion of food contaminated by fluorine-filled volcanic ash (as the specimen was found in ash-filled strata). Livestock that grazes on volcanic ash ridden fields typically die of acute intoxication within a few days or weeks.

An engraved Pseudodon shell DUB1006-fL with geometric markings could possibly be evidence of the earliest art-making, dating back to 546–436 thousand years ago. Art-making capabilities could be considered evidence of symbolic thinking, which is associated with modern cognition and behavior. Engraved lines on an ox rib, associated with Acheulean lithics, from Pech de l'Azé, France, are similar to a meander design found in modern human Upper Paleolithic cave art. Three ostrich eggshell beads associated with Achuelian lithics were found in northwestern Africa, the earliest disc beads ever found, and Acheulian disc beads have also been found in France and Israel. The Middle Pleistocene "Venus of Tan-Tan" and "Venus of Berekhat Ram" are postulated to been crafted by H. erectus to resemble a human form. They were mostly formed by natural weathering, but slightly modified to emphasize certain grooves to suggest hairline, limbs, and eyes. The former has traces of pigments on the front side, possibly indicating it was colored.

H. erectus was also the earliest human to have intentionally collected red-colored pigments, namely ochre, recorded as early as the Middle Pleistocene. Ochre lumps at Olduvai Gorge, Tanzania—associated with the 1.4 Ma Olduvai Hominid 9—and Ambrona, Spain—which dates to 424–374 thousand years ago—were suggested to have been struck by a hammer stone and purposefully shaped and trimmed. At Terra Amata, France—which dates to 425–400 or 355–325 thousand years ago—red, yellow, and brown ochres were recovered in association with pole structures; ochre was probably heated to achieve such a wide color range. As it is unclear if H. erectus could have used ochre for any practical application, ochre collection might indicate that H. erectus was the earliest human to have exhibited a sense of aesthetics and to think beyond simply survival. Later human species are postulated to have used ochre as body paint, but in the case of H. erectus, it is contested if body paint was used so early in time. Further, it is unclear if these few examples are not simply isolated incidents of ochre use, as ochre is much more prevalent in Middle and Upper Paleolithic sites attributed to Neanderthals and H. sapiens.

The inhabitants of the Chinese Zhoukoudian Peking Man site were members of some Lower Paleolithic Skull Cult because the skulls all showed fatal blows to the head, breaking in of the foramen magnum at the base of the skull, by-and-large lack of preserved facial aspects, an apparently consistent pattern of breaking on the mandible, and a lack of post-cranial remains (elements that are not the skull). He believed that the inhabitants were head hunters, and smashed open the skulls and ate the brains of their victims. However, scavenging animals and natural forces such as flooding can also inflict the same kind of damage to skulls, and there is not enough evidence to suggest man hunting or cannibalism.

Many hand axes exhibit no wear and were produced en masse, and concluded that these symmetrical, tear-drop shaped lithics functioned primarily as display tools so males could prove their fitness to females in some courting ritual, and were discarded afterwards. However, an apparent lack of reported wearing is likely due to a lack of use-wear studies, and only a few sites yield an exorbitant sum of hand axes likely due to gradual accumulation over generations instead of mass production.

Language

The vertebral column of an adolescent Turkana boy indicated that this individual did not have properly developed respiratory muscles in order to produce speech, thereby that Turkana boy was afflicted by skeletal dysplasia and scoliosis. So specimen as having a spine within the range of variation of modern human spines, contending that Turkana boy had spinal stenosis and was thus not representative of the species. Also, because he considered H. e. georgicus ancestral to all non-African H. erectus, therefore concluded that the respiratory muscles of all H. erectus (at least non-ergaster) would not have impeded vocalization or speech production.

Neurologically, all Homo have similarly configured brains, and, likewise, the Broca's and Wernicke's areas (in charge of sentence formulation and speech production in modern humans) of H. erectus were comparable to those of modern humans. However, this is not indicative of anything in terms of speech capability as even large chimpanzees can have similarly expanded Broca's area, and it is unclear if these areas served as language centers in archaic humans. A 1-year-old H. erectus specimen shows that an extended childhood to allow for brain growth, which is a prerequisite in language acquisition, was not exhibited in this species.

The hyoid bone supports the tongue and makes possible modulation of the vocal tract to control pitch and volume. A 400 thousand years ago H. erectus hyoid bone from Castel di Guido, Italy, is bar-shaped—more similar to that of other Homo than to that of non-human apes and Australopithecus—but is devoid of muscle impressions, has a shield-shaped body, and is implied to have had reduced greater horns, meaning H. erectus lacked a humanlike vocal apparatus and thus anatomical prerequisites for a modern human level of speech. Increasing brain size and cultural complexity in tandem with technological refinement, and the hypothesis that articulate Neanderthals and modern humans may have inherited speech capabilities from the last common ancestor, could possibly indicate that H. erectus used some proto-language and built the basic framework which fully fledged languages would eventually be built around.

The lower cave of the Zhoukoudian cave, China, is one of the most important archaeological sites worldwide. There have been remains of 45 homo erectus individuals found and thousands of tools recovered. Most of these remains were lost during

World War 2, with the exception of two postcranial elements that were rediscovered in China four human teeth from 'Dragon Bone Hill.

New evidence has shown that Homo erectus does not have uniquely thick vault bones, as was previously thought. Testing showed that neither Asian or African Homo erectus had uniquely large vault bones.

Most scientists currently recognize some 15 to 20 different species of early humans. They do not all agree, however, these species are related or which ones simply died out. Many early human species -- certainly the majority of them – left no living descendants. Scientists also debate over how to identify and classify particular species of early humans, and about what factors influenced the evolution and extinction of each species.

Early humans first migrated out of Africa into Asia probably between 2 million and 1.8 million years ago. They entered Europe somewhat later, between 1.5 million and 1 million years. Species of modern humans populated many parts of the world much later. For instance, people first came to Australia probably within the past 60,000 years and to the Americas within the past 30,000 years or so. The beginnings of agriculture and the rise of the first civilizations occurred within the past 12,000 years.

Paleoanthropology

Paleoanthropology is the scientific study of human evolution. Paleoanthropology is a subfield of anthropology, the study of human culture, society, and biology. The field involves an understanding of the similarities and differences between humans and other species in their genes, body form, physiology, and behavior. Paleoanthropologists search for the roots of human physical traits and behavior. They seek to discover how evolution has shaped the potentials, tendencies, and limitations of all people. For many people, paleoanthropology is an exciting scientific field because it investigates the origin, over millions of years, of the universal and defining traits of our species. However, some people find the concept of human evolution troubling because it can seem not to fit with religious and other traditional beliefs about how people, other living things, and the world came to be. Nevertheless, many people have come to reconcile their beliefs with the scientific evidence.

Early human fossils and archeological remains offer the most important clues about this ancient past. These remains include bones, tools and any other evidence (such as footprints, evidence of hearths, or butchery marks on animal bones) left by earlier people. Usually, the remains were buried and preserved naturally. They are then found either on the surface (exposed by rain, rivers, and wind erosion) or by digging in the ground. By studying fossilized bones, scientists learn about the physical appearance of earlier humans and how it changed. Bone size, shape, and markings left by muscles tell us how those predecessors moved around, held tools, and how the size of their brains changed over a long time. Archeological evidence refers to the things earlier people made and the places where scientists find them. By studying this type of evidence, archeologists can understand how early humans made and used tools and lived in their environments.

The process of evolution

The process of evolution involves a series of natural changes that cause species (populations of different organisms) to arise, adapt to the environment, and become extinct. All species or organisms have originated through the process of biological evolution. In animals that reproduce sexually, including humans, the term species refers to a group whose adult members regularly interbreed, resulting in fertile offspring -- that is, offspring themselves capable of reproducing. Scientists classify each species with a unique, two-part scientific name. In this system, modern humans are classified as Homo sapiens.

Evolution occurs when there is change in the genetic material -- the chemical molecule, DNA -- which is inherited from the parents, and especially in the proportions of different genes in a population. Genes represent the segments of DNA that provide the chemical code for producing proteins. Information contained in the DNA can change by a process known as mutation. The way particular genes are expressed – that is, how they influence the body or behavior of an organism -- can also change. Genes affect how the body and behavior of an organism develop during its life, and this is why genetically inherited characteristics can influence the likelihood of an organism's survival and reproduction.

Evolution does not change any single individual. Instead, it changes the inherited means of growth and development that typify a population (a group of individuals of the same species living in a particular habitat). Parents pass adaptive genetic changes to their offspring, and ultimately these changes become common throughout a population. As a result, the offspring inherit those genetic characteristics that enhance their chances of survival and ability to give birth, which may work well until the environment changes. Over time, genetic change can alter a species' overall way of life, such as what it eats, how it grows, and where it can live. Human evolution took place as new genetic variations in early ancestor populations favored new abilities to adapt to environmental change and so altered the human way of life.

Australopith Characteristics

Most of the distinctly human physical qualities in australopiths related to their bipedal stance. Before australopiths, no mammal had ever evolved an anatomy for habitual upright walking. African apes move around their environments in a variety of ways. They use their arms to climb and to swing through the trees (known as brachiation). They knuckle-walk when on the ground, leaning on the middle parts of their fingers. And sometimes they move on two legs, as when chimpanzees feed on low branches or when gorillas show threat displays. The australopith body was devoted especially to bipedal walking. Australopiths also had small canine teeth, as compared with long canines found in almost all other catarrhine primates.

Other characteristics of australopiths reflected their ape ancestry. Although their canine teeth were not large, their faces stuck out far in front of the braincase. Their brains were about the same size as apes' today, about 390 to 550 cubic centimeters (24 to 34 cubic in) but were enlarged relative to body size. Their body weight, which can be estimated from their bones, ranged from about 27 to 49 kg (60 to 108 lb.) and they stood about 1.1 to 1.5 m (3.5 to 5 ft) tall. Their weight and height compare closely to those of chimpanzees (chimp height measured standing). Some australopith species had a large degree of sexual dimorphism -- males were much larger than females -- a trait also found in gorillas, orangutans, and some other primates.

Australopiths also had curved powerful fingers and long thumbs with a wide range of movement. Apes, in comparison, have longer, very strong, even more curved fingers – which are advantageous for hanging and swinging from branches -- but their very short thumbs limit their ability to manipulate small objects. While the fingers were longer than in modern humans, the australopith finger bones were not so long and curved as to suggest arm swinging. It is not yet clear whether these changes in the hand of early australopiths enabled them to use tools in a better way than earlier apes or even modern chimpanzees today.

Australopithecus is a genus of early hominins that existed in Africa during the Late Pliocene and Early Pleistocene. The genus Homo (which includes modern human) emerged within Australopithecus genera Paranthropus and Kenyanthropus. Australopithecus is a member of sub-tribe Australopithe- cina which sometimes also includes Ardipithecus, though the term australopithecine is sometimes used to refer only to members of Austalopithecus. The earliest known member of the genus, A. anamensis, existed in eastern Africa around 4.2 million years ago. Australopithecus fossils become more widely dispersed throughout eastern and southern Africa (the Chadian A. bahrelghazali indicates the genus was much more widespread than the fossil record suggests, before eventually becoming extinct 1.9 million years ago (or 1.2 to 0.6 million years ago if Paranthropus is included). While none of the groups normally directly assigned to this group survived, Australopithecus gave rise to living descendants, Genus Homo emerged from an Australopithecus species at some time between 3 and 2 million years ago.

Australopithecus possessed two of three duplicated genes derived from SRGAP2 roughly 3.4 and 2.4 million years ago (SRGAP2B and SRGAP2C), the second of which contributed to the increase in number and migration of neurons in the human brain. Significant changes to the hand first appear in the fossil record of later A. afarensis about 3 million years ago (fingers shortened relative to thumb and changes to the joints between the index finger and the trapezium and capitate).

From Ape to Human

Fossils from several different early australopith species that lived between 4 million and 2 million years ago show a variety of adaptations that mark the transition from ape to human. The very early period of this transition, prior to 4 million years ago, remains poorly documented in the fossil record, but those fossils that do exist show the most primitive combinations of ape and human features.

Fossils reveal much about the physical build and activities of early australopiths, but little is known about surface physical features, such as the color and texture of skin and hair, or about certain behaviors, such as methods of obtaining food or patterns of social interaction. For these reasons, scientists study the living great apes -- particularly the African apes -- to better understand how early australopiths might have looked and behaved. The study of living apes, therefore, sheds light on how the transition from ape to human might have occurred.

For example, australopiths probably resembled the great apes in characteristics such as the shape of the face and the amount of hair on the body. Australopiths also had brains and body sizes in the same range exhibited by the great apes, leading scientists to believe that the australopiths had similar mental capabilities and possibly even social structures.

Humans place in nature relative to apes (nonhuman hominoids) and the geographic origins of the human lineage (hominins) have been heavily debated. Humans diverged from apes [specifically, the chimpanzee lineage at some point between 9.3 million and 6.5 million years ago, and habitual bipedalism evolved early in hominins (accompanied by enhanced manipulation and, later on, cognition). To understand the selective pressures surrounding hominin origins, it is necessary to reconstruct the morphology, behavior, and environment of the Pan-Homo last common ancestor. "Top-down" approaches have relied on living apes (especially chimpanzees) to reconstruct hominin origins. However, "bottom-up" perspectives from the fossil record suggest that modern hominoids represent a decimated and biased sample of a larger ancient radiation and present alternative possibilities for the morphology and geography of the Pan-Homo last common acestors. Reconciling these two views remains at the core of the human origins problem.

There is no consensus on the phylogenetic positions of the diverse

and widely distributed Miocene apes. Besides their fragmentary record, disagreements are due to the complexity of interpreting fossil morphologies that present mosaics of primitive and derived features, likely because of parallel evolution (e.g., homoplasy). This has led some authors to exclude known Miocene apes from the modern hominoid radiation. However, most researchers identify some fossil apes as either stem or crown members of the hominid clade [i.e., preceding the divergence between orangutans (pongines) and African great apes and humans (hominines), or as a part of the modern great ape radiation]. European Miocene apes have prominently figured in discussions about the geographic origin of hominines. "Kenyapith" apes dispersed from Africa into Eurasia ~16 to 14 million years ago, and some of them likely gave rise to the European "dryopith" apes and the Asian pongines before 12.5 million years ago. Some experts interpret dryopiths as stem hominines and support their back-to-Africa dispersal in the latest Miocene, subsequently evolving into modern African apes and hominins. Others interpret dryopiths as broadly ancestral to hominids or an evolutionary dead end.

Increased habitat fragmentation during the late Miocene in Africa might explain the evolution of African ape knuckle walking and hominin bipedalism from an orthograde arboreal ancestor. Bipedalism might have allowed humans to escape the great ape "specialization trap", an adaptive feedback loop between diet, specialized arboreal locomotion, cognition, and life history. However, understanding the different selection pressures that underlie knuckle walking and bipedalism is hindered by locomotors uncertainties about the Pan-Homo last common ancestors and its Miocene forebears. In turn, the functional interpretation of Miocene ape mosaic morphologies is challenging because it depends on the relevance of primitive features. Furthermore, adaptive complexes can be co-opted to perform new functions during evolution. For instance, features that are functionally related to quadrupedalism or orthogrady can be misinterpreted as bipedal adaptations. Miocene apes show that the orthograde body plan, which predates below-branch suspension, is likely an adaptation for vertical climbing that was subsequently co-opted for other orthograde behaviors, including habitual bipedalism.

Future research efforts on hominin origins should focus on fieldwork in unexplored areas where Miocene apes have yet to be found, methodological advances in morphology-based phylogenetics and paleoproteomics to retrieve molecular data beyond ancient DNA limits, and modeling driven by experimental data that integrates morphological and biomechanical information, to test locomotors inferences for extinct taxa. ( taxa is units of taxonomic from lower to higher degree of improvement ) It is also imperative to stop assigning a starring role to each new fossil discovery to fit evolutionary scenarios that are not based on testable hypotheses.

Early hominins likely originated in Africa from a Miocene last common ancestors that does not match any living ape (e.g., it might not have been adapted specifically for suspension or knuckle walking). Despite phylogenetic uncertainties, fossil apes remain essential to reconstruct the "starting point" from which humans and chimpanzees evolved.

Bipedalism

The anatomy of australopiths shows a number of adaptations for bipedalism. Adaptations in the lower body included the following: The australopith ilium, or pelvic bone, which rises above the hip joint, was much shorter and broader than it is in apes. This new shape enabled the hip muscles to steady the body during each bipedal step. The australopith pelvis overall had evolved a more bowl-shaped appearance, which helped support the internal organs during upright stance. The upper legs angled inward from the hip joints, which positioned the knees to better support the body during upright walking. The legs of apes, on the other hand, are positioned almost straight down from the hip, so that when an ape walks upright for a short distance, its body sways from side to side. The australopith foot was also reshaped, including shorter and less flexible toes than an ape's, which provided a more rigid lever for pushing off the ground during each step.

Other adaptations occurred above the pelvis. The australopiths' spine had an S-shaped curve, which shortened the overall length of the torso and gave rigidity and balance when standing. By contrast, apes have a relatively straight spine. The australopith skull also had an important adaptation related to bipedalism. The opening at the bottom of the skull, known as the foramen magnum, where the spinal cord attaches to the brain, was more forward than it is in apes. This position set the head in balance over the upright spine.

Australopiths clearly walked upright on the ground, but paleoanthropologists debate about whether the earliest humans also spent a lot of time in the trees. Certain physical features indicate that they spent at least some of their time in the trees. Such features include their curved and elongated fingers and elongated arms.

Explanation of Bipedalism

Many different explanations have been offered to account for the evolution of upright walking. Some of the ideas include: (1) freeing the hands, which was advantageous for carrying food or tools; (2) improved vision, especially to see over tall grass; (3) reducing the body's exposure to hot sun, which allowed better cooling during the day in an open landscape; (4) hunting or weapon use, which was easier with upright posture; and (5) feeding from bushes and low branches, which was easier when standing and moving upright between closely spaced bushes.

Although none of these has overwhelming support, recent study of chimpanzees favors the last one. Chimps move on two legs most often when feeding on the ground from bushes and low branches. Chimps today are not, however, very good at walking in this way over long distances. As the distances between trees or groves of trees became wider during drier periods bipedal behavior in pre-human populations may have become more frequent. Accordingly, a more effective bipedal gait was favored not as an adaptation to savanna living but rather as a way of crossing less favored areas of open terrain. An ability to climb trees continued to be important. This idea may currently be the best explanation for the unique adaptation of the early australopiths: a combination of long, powerful arms, slightly elongated legs, and lower limbs reshaped for upright walking over long distances on the ground.

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Small Canine Teeth

Compared with apes, humans have very small canine teeth. Apes, particularly males, have thick, projecting, sharp canines that they use for displays of aggression and as weapons to defend themselves. By 4 million years ago, australopiths had developed the human characteristic of having smaller, flatter canines. Canine reduction might have related to an increase in social cooperation among humans and an accompanying decrease in the need for males to make aggressive displays.

Australopithecus Afarensis

Australopithecus anamensis was quite similar to another, much better-known species, australopith afarensis, a gracile australopith that thrived in eastern Africa between about 3.9 million and 3 million years ago. The most celebrated fossil of Lucy, a partial skeleton of a female at Hadar, Ethiopia. Lucy lived 3.2 million years ago. Several hundred fossils of this species have been described from Hadar, including a collection representing at least 13 individuals of both sexes and various ages, all from a single site that is dated 3.2 million years old.

Workers in northern Tanzania have also found fossilized bones of australopith afarensis at Laetoli, a 3.6 million year old site best known for spectacular trails of bipedal human footprints (and the prints of other animals) preserved in a hardened volcanic ash. These footprints provide irrefutable evidence that australopiths regularly walked bipedally.

Australopithecus afarensis had a tall face, a delicate brow ridge, and prognathism (the jaw jutted outwards). The jawbone was quite robust, similar to that of gorillas. The living size of A. afarensis is debated, with arguments for and against marked size differences between males and females. Lucy measured perhaps 105 cm (3 ft 5 in) in height and 25–37 kg (55–82 lb), but she was rather small for her species. In contrast, a presumed male was estimated at 165 cm (5 ft 5 in) and 45 kg (99 lb). A perceived difference in male and female size may simply be sampling bias. The leg bones as well as the Laetoli fossil track ways suggest A. afarensis was a competent biped, though somewhat less efficient at walking than humans. The arm and shoulder bones have some similar aspects to those of orangutans and gorillas, which has variously been interpreted as either evidence of partial tree-dwelling (arboreality), or basal traits inherited from the chimpanzee–human last common ancestor with no adaptive functionality.

A. afarensis was probably a generalist omnivore of both C3 forest plants and C4 CAM savanna plants—and perhaps creatures which ate such plants—and was able to exploit a variety of different food sources. Similarly, A. afarensis appears to have inhabited a wide range of habitats with no real preference, inhabiting open grasslands or woodlands, shrub lands, and lake- or riverside forests. Potential evidence of stone tool use would indicate meat was also a dietary component. Marked sexual dimorphism in primates typically corresponds to a polygynous society and low dimorphism to monogamy, but the group dynamics of early hominins is difficult to predict with accuracy. Early hominins may have fallen prey to the large carnivores of the time, such as big cats and hyenas.

The controversy about how the australopiths moved has mainly focused on Lucy's species australopith afarensis. While Lucy certainly walked upright, she stood only 3.5 feet tall and had longer, more powerful arms than most latter human species, which suggests that she was also adept at climbing trees. And while the Laetoli footprints were made by bipedal humans, some scientists have argued that the imprints of the heel, arch, and toes are not exactly like those made by modern human feet. In addition, other fossils from Hadar and Laetoli come from individuals much larger than Lucy, up to 5 feet tall. This has caused controversy over whether the entire set of fossils represents one or two species, although most scientists accept the single-species idea since large and small adults, probably male and female, occurred together at the same site at Hadar.

Another controversy arises from the claim that australopith. afarensis was the common ancestor of both later australopiths and the modern human genus, Homo. While this idea remains a strong possibility, the similarity between australopithecus afarensis and another australopith species -- one from southern Africa, named Australopithecus africanus -- makes it difficult to decide which of the two species gave rise to the genus Homo.

Australopithecus Africanus

Australopithecus africanus thrived in what is now the Transvaal region of South Africa between about 3.5 million and 2.5 million years ago. The anatomist described this species -- the first known australopith -- on the basis of a fossil discovered at Taung, South Africa. For two decades after this discovery, almost no one in the scientific community believed that the skull came from an ancestral human. Paleontologists unearthed many more australopith skulls and other bones from the Transvaal sites of Sterkfontein and Swartkrans.

Australopithecus africanus generally had a more globular braincase and less primitive-looking face and teeth than did Australopithecus afarensis. Thus some scientists consider the southern species of early australopith to be a likely ancestor of the genus Homo. According to scientists Australopithecus africanus had facial features that mark it on the path to the robust australopiths found later in the same region. Some recent finds from the Transvaal site of Sterkfontein indeed have begun to blur the distinction between the early australopiths and the later robust species. Paleoanthropologists unearthed an almost complete early australopith skeleton at Sterkfontein. Although it may prove to be a new species, this important find may resolve some of the questions about where Australopithecus africanus fits in the story of human evolution.

Australopithecus africanus existed between 3 and 2 million years ago. It is similar to afarensis, and was also bipedal, but body size was slightly greater. Brain size may also have been slightly larger, ranging between 420 and 500 cubic centimeters. This is a little larger than chimp brains (despite a similar body size), but still not advanced in the areas necessary for speech. The back teeth were a little bigger than in afarensis. Although the teeth and jaws of africanus are much larger than those of humans, they are far more similar to human teeth than to those of apes.

The shape of the jaw is now fully parabolic, like that of humans, and the size of the canine teeth is further reduced compared to afarensis.

Australopithecus garhi

It is known from a partial skull. The skull differs from previous australopithecine species in the combination of its features, notably the extremely large size of its teeth, especially the rear ones, and a primitive skull morphology. Some nearby skeletal remains may belong to the same species. They show a humanlike ratio of the humerus and femur, but an apelike ratio of the lower and upper arm.

Australopithecus afarensis and africanus, and the other species above, are known as gracile australopithecines, because of their relatively lighter build, especially in the skull and teeth. (Gracile means "slender", and in paleoanthropology is used as an antonym to "robust".) Despite this, they were still more robust than modern humans.

Australopithecus aethiopicus

Australopithecus aethiopicus existed between 2.6 and 2.3 million years ago. This species is known from one major specimen, the Black Skull. It may be an ancestor of robustus and boisei, but it has a baffling mixture of primitive and advanced traits. The brain size is very small, at 410 cubic cetimeters, and parts of the skull, particularly the hind portions, are very primitive, most resembling afarensis. Other characteristics, like the massiveness of the face, jaws and single tooth found, and the largest sagittal crest in any known hominid, are more reminiscent of A. boisei. A sagittal crest is a bony ridge on top of the skull to which chewing muscles attach

Australopithecus robustus

Australopithecus robustus had a body similar to that of africanus, but a larger and more robust skull and teeth. It existed between 2 and 1.5 million years ago. The massive face is flat or dished, with no forehead and large brow ridges. It has relatively small front teeth, but massive grinding teeth in a large lower jaw. Most specimens have sagittal crests. Its diet would have been mostly coarse, tough food that needed a lot of chewing. The average brain size is about 530 cubic centimeters. Bones excavated with robustus skeletons indicate that they may have been used as digging tools.

Australopithecus boisei was Zinjanthropus boisei

Australopithecus boisei existed between 2.1 and 1.1 million years ago. It was similar to robustus, but the face and cheek teeth were even more massive, some molars being up to 2 cm across. The brain size is very similar to robustus, about 530 cc. Experts consider boisei and robustus to be variants of the same species.

Australopithecus aethiopicus, robustus and boisei are known as robust australopithecines, because their skulls in particular are more heavily built.

The Later Australopiths

By 2.7 million years ago, the robust australopiths had evolved. The robust australopiths represent an intriguing group of early humans because they survived for a long time and were quite common compared to other early human species. They had adaptations that differed from the larger-brained populations of Homo who lived at the same time, but then mysteriously became extinct by one million years ago.

Although the word "robust" originally referred to the larger body once believed to exist in these australopiths, they are now known to have been roughly the same size as australopith afarensis and australopith africanus. Instead, "robust" accurately describes the very massive molar teeth, face, and skull muscle markings that characterized these species. The robust australopiths had megadont cheek teeth -- broad, thick-enameled molars and premolars -- which formed a flattened and worn surface. Their incisor teeth, by contrast, were small. An expanded, flattened, and more vertical face accompanied this emphasis on the back teeth. The combination of broad molars and large face was effective in absorbing the stresses of strong chewing. Along the top of the head was a sagittal crest, a raised area of bone along the skull's midline from front to back, where thick muscles that moved the jaw up and down were attached.

The bars of bone along each side of the skull (the zygomatic arches) were positioned far to the side, which allowed huge openings for the chewing muscles near where they attached to the lower jaw. Altogether, these traits indicate very powerful and prolonged chewing of food. A similar expansion in the chewing structures can be seen in other groups of plant-eating animals. Microscopic wear on the teeth of paranthropus robustus and paranthropus boisei appear to support the idea of a vegetarian diet. It is thought that the robust australopiths had a diet consisting of tough, fibrous plant food, such as seed pods and underground tubers. However, chemical studies of fossil bones suggest that the southern species may also have eaten animals.

Because they share the features of heavy chewing, the robust australopiths appear to represent a distinct evolutionary group of early humans. Many paleoanthropologists have linked the robust species together with a unique genus name, Paranthropus (the name originally given to the southern robust species). This classification implies that the first robust species, paranthropus aethiopicus, became separated from the other australopiths and then evolved into paranthropus boisei and paranthropus robustus (the other two robust species). Other researchers have kept the robust species within the genus Australopithecus, stating that the eastern forms (A. aethiopicus and A. boisei) evolved their massive teeth from the early australopiths of the region (perhaps A. afarensis), whereas the southern species (robustus) evolved independently from A. africanus. If this type of parallel evolution occurred, the robust species would form two separate side branches of the human family tree. Due to alternative views such as this, the robust species are often known by more than one name (such as Australopithecus boisei and Paranthropus boisei).

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Paranthropus Aethiopicus

The earliest known robust species, Paranthropus aethiopicus, had evolved in eastern Africa by 2.7 million years ago. In 1985 at West Turkana, Kenya, paleoanthropologists discovered the fossil skull that defined this species. It became known as the "black skull" because of the color it had absorbed from minerals in the ground. The skull, dated 2.5 million years old, had a tall sagittal crest toward the back of its cranium and a face that projected far outward from the forehead. Paranthropus aethiopicus shares some primitive features with Australopithecus afarensis -- that is, features that originated in the earlier East African australopith. This may indicate that paranthropus aethiopicus evolved from Australopithecus afarensis.

Paranthropus aethiopicus is an extinct species of robust australo-

pithecine from the Late Pliocene to Early Pleistocene of East Africa about 2.7–2.3 million years ago. However, it is much debated whether or not Paranthropus is an invalid grouping and is synonymous with Australopithecus, so the species is also often classified as Australopithecus aethiopicus Whatever the case, it is considered to have been the ancestor of the much more robust P. boisei. It is debated if P. aethiopicus should be subsumed under P. boisei, and the terms P. boisei sensu lato ("in the broad sense") and P. boisei sensu stricto ("in the strict sense") can be used to respectively include and exclude P. aethiopicus from P. boisei.

Like other Paranthropus, P. aethiopicus had a tall face, thick palate, and especially enlarged cheek teeth. However, likely due to its archaicness, it also diverges from other Paranthropus, with some aspects resembling the much earlier A. afarensis. P. aethiopicus is known primarily by the skull KNM WT 17000 from Koobi Fora, Lake Turkana, Kenya, as well as some jawbones from Koobi Fora; the Shungura Formation, Ethiopia; and Laetoli, Kenya. These locations featured bushland to open woodland landscapes with edaphic water-logged) grasslands.

By this point in time, much younger robust australopithecines had been reported from South Africa (robustus) and East Africa (boisei), and been variously assigned to either Australopithecus or a unique genus Paranthropus. It is noted several anatomical differences, but were unsure if this stemmed from the specimens archaicness or represented the normal range of variation for the species.

The discovery of these archaic specimens overturned previous postulations that P. robustus was the ancestor of the much more robust P. boisei by establishing the boisei lineage as beginning long before robustus had existed.

Several more lower and upper jaw specimens have been unearthed in the Shungura Formation, including a juvenile specimen. Also found was the upper portion of a tibia and thus with P. aethiopicus.

It is also debated if Paranthropus is a valid natural grouping (monophyletic) or an invalid grouping of similar-looking hominins (paraphyletic). Because skeletal elements are so limited in these species, their affinities with each other and to other australopithecines is difficult to gauge with accuracy. The jaws are the main argument for monophyly, but such anatomy is strongly influenced by diet and environment, and could in all likelihood have evolved independently in P. boisei and P. robustus. Proponents of monophyly consider P. aethiopicus to be ancestral to the other two species, or closely related to the ancestor. Proponents of paraphyly allocate these three species to the genus Australopithecus as A. boisei, A. aethiopicus, and A. robustus.

Typical of Paranthropus, KNM WT 17000 is heavily built, and the palate and base of the skull are about the same size as the P. boisei holotype OH 5. The brain volume of KNM WT 17000 was estimated to have been 410 cc (25 cu in), which is smaller than that of other Paranthropus. The combination of a tall face, thick palate, and small braincase caused a highly defined sagittal crest on the midline of the skull. The only complete tooth crown of the specimen is the right third premolar, whose dimensions are well above the range of variation for P. robustus and on the upper end for P. boisei. Unlike other Paranthropus, KNM WT 17000 did not have a flat face, and the jaw jutted out (prognathism).

In regard to the temporal bone, KNM WT 17000 differs from other Paranthropus in that: the squamous part of temporal bone is extensively pneumaticized, the tympanic part of the temporal bone is not as vertically orientated, the base of the skull is weakly flexed, the postglenoid process is completely anterior to (in front of) the tympanic, the tympanic is somewhat tubular

, and the articular tubercle is weak. Like P. boisei, the foramen magnum where the skull connects to the spine is heart-shaped. The temporalis muscle was probably not directed as forward as it was in P. boisei, meaning the P. aethiopicus jaw likely processed food with the incisors before using the cheek teeth. The incisors of P. boisei are thought to have not been involved in processing food. The long distance between the first molar and the jaw hinge would suggest KNM WT 17000 had an exceptionally long ramus of the mandible (connecting the lower jaw to the skull), though the hinge's location indicates the ramus would not have been particularly deep (it would have been weaker). This may have produced a less effective bite compared to P. boisei.

Cast of the Peninj Mandible assigned to P. boisei, which is similar to KNM-WT 16005 is quite similar to the Peninj Mandible assigned to P. boisei, exhibiting postcanine megadontia with relatively small incisors and canines (based on the tooth roots) and large cheek teeth. Nonetheless, the incisors were likely much broader in KNM-WT 16005. KNM-WT 16005 preserved four cheek teeth on the left side: the third premolar measuring 10.7 mm × 13.8 mm (0.42 in × 0.54 in), the fourth premolar measuring 12 mm × 15 mm (0.47 in × 0.59 in), the first molar measuring 15.7 mm × 14.3 mm (0.62 in × 0.56 in), and the second molar measuring 17 mm × 16.7 mm (0.67 in × 0.66 in). The fourth premolar and first molar are a little smaller than those of the Peninj mandible, and the second molar a bit bigger. The KNM-WT 16005 jawbone is smaller than what KNM WT 17000 would have had.

Many of these P. aethiopicus features are shared with the early A. afarensis, further reiterating the species' archaicness. In general, Paranthropus are thought to have been generalist feeders, with the heavily built skull becoming important when chewing less desirable, lower quality foods in times of famine. Unlike P. boisei which generally is found in the context of closed, wet environments, P. aethiopicus seems to have inhabited bushland to open woodland habitats around edaphic (water-logged) grasslands. The Omo–Turkana Basin 2.5 million years ago (at the Pliocene/Pleistocene border) featured a mix of forests, woodlands, grasslands, and bushlands, though grasslands appear to have been expanding through the Early Pleistocene. Homo seems to have entered the region 2.5–2.4 million years ago.

Paranthropus aethiopicus is an extinct species of robust australopithecine from the late Pliocene to early Pleistocene of East Africa about 2.7 – 2.3 million years ago. It is considered to have been the ancestor of the much more robust P. boisei. Like other Paranthropus, P. aethiopicus had a tall face, thick palate, and especially enlarged cheek teeth. However, likely due to its archaicness, it also diverges from other Paranthropus, with some aspects resembling the much earlier A. afarensis. P. aethiopicus is known primarily by the skull as well as some jawbones from Koobi Fora; the Shungura Formation, Ethiopia; and Laetoli, Kenya. These locations featured bush land to open wood land landscapes with edaphic water-logged grasslands.

The genus Paranthropus otherwise known as "robust australopithecines" typically includes P. aethiopicus, P. boisei, and P. robustus. P. aethiopicus is the earliest member of the genus, with the oldest remains, from the Ethiopian Omo Kibish Formation, dated to 2.6 million years ago at the end of the Pliocene. It is possible that P. aethiopicus evolved even earlier, up to 3.3 million years ago, on the expansive Kenyan flood plains of the time. P. aethiopicus is only confidently identified from the skull and a few jaws and isolated teeth, and is generally considered to have been ancestral to P. boisei which also inhabited East Africa, making it a chrono species. Because of this relationship, it is debatable if P. aethiopicus should be subsumed under P. boisei or if the differences stemming from archaicness should justify species distinction. The terms P. boisei sensu lato ("in the broad sense") and P. boisei sensu stricto ("in the strict sense") can be used to respectively include and exclude P. aethiopicus from P. boisei when discussing the lineage as a whole.

Paranthropus Boisei

Paranthropus boisei, the other well-known East African robust australopith, lived over a large geographic range between about 2.3 million and 1.2 million years ago. New World Central Hub scientists discovered the first fossil of this species -- a nearly complete skull at the site of Olduvai Gorge in Tanzania. Paleoanthropologist explorer and researcher named the new species Zinjanthropus boisei (Zinjanthropus translates as "East African man"). This skull, which is dated to 1.8 million years ago, has the most specialized features of all the robust species. It has a massive, wide, and dished-in face that was capable of withstanding extreme chewing forces, and its molars are four times the size of those in modern humans. Since the discovery of Zinjanthropus, now recognized as an australopith, scientists have found great numbers of paranthropus boisei fossils in Tanzania, Kenya, and Ethiopia.

Paranthropus boisei was a long-lived species of archaic hominin that first evolved in East Africa about 2.3 million years ago. The first skull of Paranthropus boisei, dated to 1.75 million years old, was discovered at Olduvai. A number of hominin's skull fossils have been discovered over the years, but the build and skeletal adaptations of the rest of the Paranthropus boisei's body have been unknown, until now. During Olduvai excavations unearthed the partial skeleton of a large adult individual who is represented by various teeth and skeletal parts.

This is the first time we've found bones that suggest that this creature was more ruggedly built – combining terrestrial bipedal locomotion and some arboreal behaviors – than we'd previously thought. It seems to have more well-formed forearm muscles that were used for climbing, fine-manipulation and all sorts of behavior We are starting to understand the physiology of these individuals of this particular species and how it actually adapted to the kind of habitat it lived in. We knew about the kind of food it ate – it was omnivorous, leaning more toward plant material – but now we know more how it walked around and we know it was a tree climber. The size of the arm bones suggests strong forearms and a powerful upper body. It's a different branch on our ancestry tree. It came later than the other hominins, so the question now is what happened to it? We're going to do more work on biomechanics and see what else this creature was doing. The Paranthropus boisei individual likely stood 1.0 to 1.4 meter tall and possessed a robust frame.

Paranthropus Robustus

The southern robust species, which has the descriptive name Paranthropus robustus, lived between about 1.8 million and 1.3 million years ago in the Transvaal, the same region that was home to australopith africanus. In 1938 many australopith africanus fossils, both a fossil jaw and molar that looked distinctly different from those in australopith africanus. After finding the site of Kromdraai, from which the fossil had come many more bones and teeth that together convinced scientists to name a new species, which they called Paranthropus robustus (Paranthropus meaning "beside man").

The Fate of the Later Australopiths

The youngest fossils of robust australopiths are about 1.2 million years old, which suggests that they became extinct by around then. At about that time world climate began to fluctuate in a different pattern, and that may have reduced the food supply on which the robust species depended. Interaction with other early humans, such as Homo erectus, has been suggested as another reason for their extinction, although no compelling evidence exists of direct contact between these species. Competition with several other species of plant-eating monkeys and pigs, which thrived in Africa in the time, may have been an even more important factor. Still, the reasons why the robust australopiths became extinct, after such a successful time, are unknown.

Fossil Find Improves Knowledge of Human Origins

New found fossils from Ethiopia are giving scientists a clearer glimpse into the murky origins of a hominid species that was an important link in the evolution of ape to man. The 4-million-year-old fossils belong to Australopithecus anamensis, the earliest known member of Australopithecus, the genus right before our own, Homo.

The new bones which include a femur, several teeth and the largest jaw fragment ever recovered from any hominid - were discovered last December 2005 in the Middle Awash valley of Ethiopia, a region well-known for its rich deposit of hominid fossils. The fossils were found sandwiched between sediment layers containing the fossils of an earlier species, Ardipithecus ramidus, and the geologically younger Australopithecus afarensis.

This is the first time these three species have been found together in one geographic location and in such a tight chronological order, scientists say.

Filling in the Gaps

The Middle Awash valley of Ethiopia has the longest and most continuous record of human evolution of any place on Earth. Scientists have found the fossils of nearly 250 hominid specimens embedded within more than a mile of stacked sediments representing time periods that stretch back 6 million years.

The fossils of Ar. ramidus, Au. anamensis and Au. afarensis follow on the heels of one another in Middle Awash's sediment layers - appearing at roughly 4.4 million, 4.2 million years ago and 3.6 million years ago, respectively - allowing scientists to accurately pinpoint the time when Australopithecus first appeared.

"The origins of Australopithecus have always been tricky, but now we have enough fossil evidence to indicate that the first occurrence of Australopithecus occurred 4.2 million years ago. Since their remains don't overlap, scientists think the three species are directly related, evolving one from the other, rather than being cousins that shared a common ancestor." This discovery fills the gap between Ardipithicus and Australopithecus." Here is one place on Earth where you have 12 separate sediment layers, one stacked on top of another, whose fossils have filled in many of the gaps in human evolution over the years. "Many of the links are no longer missing." Ape to Man.

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