1. Discuss the modern theory of human evolution. Include a description of early humans and their unique advancements.

The human species is a member of the mammalian order Primates. It is related, in descending order of closeness, to apes, monkeys, tarsiers, and lemurs. The early part of human evolutionary history, therefore, is the story of the emergence of the ancestors of these groups. The earliest traces of fossil primates are found in rocks about 70 million years old, which also contain the remains of the last dinosaurs. Within a few million years the dinosaurs had disappeared, and mammals, including primates, became much more common. The remains of these very early primates, which are quite common in fossil sites of the American West and Western Europe, indicate that they were a diverse group of small, rat-like animals, some already adapted to life in the trees.

By about 45 million years ago a side branch of this primitive ancestral group had given rise to more advanced primates that were quite similar to modern lemurs. Among this group can be seen characteristics that are distinctive of modern primates: relatively large brains, a well-developed visual sense, and nails rather than claws. All of these characteristics were evidently adapted for life in the trees.

About 35 million years ago appeared the first evidence of primitive monkeylike primates. The largest and best known of these Propliopithecus, was about the size of a cat and is believed to be in the ancestral line of apes and humans. Although still primitive in some respects, primates of this period constitute a link between the earlier, lemurlike primates and the true monkeys and apes that first appeared about 22 million years ago, at the beginning of the long geological epoch known as the Miocene. From rocks of this age have been found the earliest fossils representing the primates of sub-Saharan Africa, the home of many living monkeys and apes and the probable place of origin of the human family.

Early Miocene apes and monkeys probably behaved and looked not unlike their living relatives. Among the apes was the group called Dryopithecus, believed to include the evolutionary ancestor of both hominids and apes such as the chimpanzee and gorilla. For most of the Miocene, Dryopithecus was widespread and successful. However, as the climate grew drier, Dryopithecus disappeared from the fossil record. Presumably, it retreated with the forests to the tropical regions where the great apes still survive.

For many years anthropologists assumed that the origin of hominids as a group separate from apes must have occurred in Europe between 14 and 10 million years ago. Most anthropologists now believe that the split occurred much later and that it occurred in Africa. Oreopithecus, an apelike primate that lived in Europe about 10 million years ago was proposed as the first hominid, but it is now believed that this primate died out completely without leaving descendants. Likewise, Ramapithecus and its close relative Sivapithecus were once championed as the first hominids. It was argued that Ramapithecus, in common with the hominids, had adapted to life outside the forest and lived off the hard, tough vegetable foods of the grasslands. It is, however, highly unlikely that Ramapithecus walked upright or used tools more than living apes. Moreover, most anthropologists now feel that its early origin rule out the possibility that it was a hominid. Pointing to the remarkable similarity in blood chemistry and genetics between chimpanzees and humans, they maintain that the earliest hominids originated from an apelike stock no more than 8 million years ago. In this case, the earliest true hominid is probably Australopithecus.

The genus Australopithecus, first described on the basis of a single skull from South Africa, is now represented by many fossils from several areas of the African continent. Important sites include Olduvai Gorge, Tanzania; Lake Rudolf (Turkana), Kenya; and Hadar, Ethiopia. The genus appears to have been confined to Africa, where it existed during the time range between 5.5 and 1 million years ago.

Although primitive in some respects, Australopithecus is classified within the human family, Hominidae, because it shares with humans certain significant advances over earlier forms. In particular, its leg bones show that it walked upright; its brain, although still within the ape range, was relatively larger than that of most apes; and neither sex had the projecting canine teeth (fangs) that are used by apes in fighting. Presumably, Australopithecus used simple clubs or threw stones to defend itself. The genus varied considerably in size--from less than 1.2 m (4 ft) to about the size of a modern human.

At least five species are generally distinguished. Australopithecus ramidus (the most recently found, and oldest, fossil), A. afarensis, and A. africanus, are small, gracile, older forms whose fossilized bones have been found in southern and eastern Africa. A. boisei and A. robustus are larger, more specialized and robust species which overlap in time with early members of the genus Homo and which evidently became extinct. An australopithecine fossil known as the "black skull," similar to A. boisei, is thought by some to represent a new species.

All species of Australopithecus lived in open woodland and grassland rather than in forests as had the apes, and the ways in which they differ physically from apes can be seen as adaptations to the new habitat. Whereas their front teeth were quite small, their back, grinding teeth (molars and premolars) were huge--evidently an adaptation to hard chewing. Studies of minute scratches on their dental enamel suggest that their diet consisted largely of hard, chewy seeds and berries. Although Australopithecus probably ate small animals, as do chimpanzees, most scientists consider it unlikely that Australopithecus was a systematic hunter, or "killer ape," as this species used to be depicted.

Whether Australopithecus regularly made and used tools is a matter of debate. Some paleoanthropologists have suggested that the broken bones and tusks of antelopes and other animals found at Makapansgat, South Africa, and at other Australopithecus cave sites may have been used as tools and weapons; other paleoanthropologists, however, consider it more likely that the broken animal bones were the leavings of leopards and hyenas that also frequented the caves. Although some sites with Australopithecus fossils have also yielded well-made stone tools, these tools are more likely to be the handiwork of early, true humans, whose remains are also found at these sites. If, as seems probable at present, Australopithecus was no more of a hunter and toolmaker than the modern chimpanzee, why did it, unlike the apes, develop two-legged locomotion, or bipedalism? The reasons for this development, too, are debated.

One theory is that Australopithecus babies were more helpless and had to be carried in the arms of their mothers. Another emphasizes the importance of free hands to an animal that had no large fangs to defend itself. Yet another sees the advantage of bipedalism as freeing the hands to gather the small, scattered vegetable foods on which Australopithecus usually fed. These ideas are not mutually exclusive. The brain of Australopithecus, although less than half the size of a modern human's, was relatively larger than that of an ape. Brain expansion may have been favored by a more complex social organization, perhaps one in which "families" of one adult male and one or more females and their young clustered in troops for protection.

From deposits dating from about 2 million years ago have emerged the first direct evidence of behavior that decisively separates the species Homo from other animals. This behavior includes the regular use of stone tools and other artifacts and the life-style called hunting and gathering. In contrast to the foraging of non-human primates, the hunting and gathering of the first humans involved a division of labor. Some group members (probably males) hunted animals for meat, whereas the rest searched for small game and wild vegetable foods. All shared the food they collected. This cooperative way of life strongly favored the evolution of technology (cutting tools and containers, especially).

Additionally, there is evidence that these early humans meticulously planned their hunts. So the human capacity for abstract thought, foresight, and adaptation to local conditions of life also apparently improved. The evidence for these changes is seen in the gradually increasing size of the brain, the development of increasingly complex technology (represented by stone working), and the rapid geographical spread of the human species.

After the extinction of Australopithecus, no more than one hominid species existed at any time. However, the single human species is given different names at different stages of its evolution. The earliest humans are known as Homo habilis. Physically, they were much like Australopithecus, apart from the larger size of their brains. Most Homo habilis fossils have been discovered in East Africa. They are often found with simple oldowan tools, including stone choppers, cores, and sharp-edged flakes. At some sites evidence exists that animals up to hippopotamus size were butchered and eaten, but whether the meat was obtained by hunting or by scavenging the carcasses of dead animals has not been determined.

As well as favoring the evolution of the brain, the early development of technology and culture also affected the evolution of the teeth and jaws. As tools (and later fire) were used to prepare and soften food, the teeth of early humans became smaller and the jaws less robust. By about 1.6 million years ago, these trends had produced a mentally and physically more advanced population called Homo erectus. At about the same time, the hand ax, a finely chipped, versatile, two-edged stone implement first appeared. Hand axes typify the acheulean tool industry, which also included a variety of pounders and flakes.

Although first recognized in Asia, Homo erectus populations also lived throughout the warmer parts of the Old World. In Europe the jaw of Heidelberg man and many scattered hand axes attest to their presence (although some researchers consider this fossil to belong to an archaic Homo sapiens). In Africa both fossil remains and habitation sites have been found throughout the length of the continent, from Algeria to South Africa. On the whole, Homo erectus seems to have preferred open or lightly wooded country, where game would have been most plentiful. Many sites attest to the skill of these people in hunting big game--elephants, antelope, and even giant baboons--as well as gathering small game and vegetable foods. Although the colder regions of the far north were not inhabited, Homo erectus was sufficiently adaptable to survive in a variety of habitats, from tropical Africa to chilly central China. Undoubtedly, the more rigorous climate of the north stimulated technological inventions. One of the most important of these was the use of fire, in cooking, for warmth, and in the hunt. This vital step probably occurred about 500,000 years ago.

By about 250,000 years ago humans had become sufficiently advanced to be assigned to Homo sapiens. However, until about 40,000 years ago, they were not identical to modern humans. They retained many ancestral features recalling Homo erectus: a large face with big teeth and a low skull with heavy brow ridges and little or no forehead. In brain size, however, they were within the modern range, which distinguishes them from the small-brained Homo erectus. Fossils of these archaic humans have been found at many sites: among the best-known early specimens are the skulls from Steinheim, Germany; Swanscombe, England; and Broken Hill, Zambia.

An important sign of technological advance was the invention, about 100,000 years ago, of the Levallois technique of stone working, in which a large thin flake is struck from a core and used as a blank for making more specialized tools such as knives and scrapers. As human populations began to exploit a wider variety of habitats, new, local tool traditions appeared: the Fauresmith on the plains of South Africa, the Sangoan on the fringes of the African forest, and the mousterian in the frigid plains of glacial Europe.

The makers of the Mousterian tools were the neandertalers (Homo sapiens neanderthalensis), who flourished between 100,000 and 40,000 years ago. Far from being the brutish "apemen" of popular imagination, the Neanderthalers were an advanced human group whose ingenuity enabled them to wrest a living from the most challenging habitat then occupied by humankind. Mousterian tools were adapted to a wide variety of tasks: cutting and preparing meat, scraping hides, working wood, and many others. Evidence of rituals--and careful burial of the dead--suggests the existence of religious beliefs. Some of the burials are of aged or handicapped people who must have been supported by the rest of the group. Given the evidence for ritual and complex beliefs, it is likely that the brain of archaic Homo sapiens was sufficiently evolved to permit the use of true language. However, anthropologists are divided over whether the Neanderthalers' vocal chords were developed enough to be capable of human speech.

About 40,000 years ago humans of modern type replaced the archaic humans such as the Neandertalers. Some anthropologists believe that only a very few archaic populations evolved directly into Homo sapiens sapiens (the taxonomic classification of fully modern humans), the rest being displaced as the moderns expanded their range. Others hold that archaic groups everywhere became "modern" by evolutionary change. Both ideas are probably to some extent correct; evolution of archaic populations into the modern human type probably occurred in many regions, but in other regions, such as western Europe, the archaics may have been absorbed and displaced by invading modern populations.

In Europe and elsewhere in the Old World the remains of the earliest physically modern humans occur with tools that attest to the invention of new techniques of manufacture, especially the production of long, narrow flake tools, called blades. These innovations define a new period of prehistory, the Upper Paleolithic. In the Old World this period began about 40,000 years ago, in the middle of the last glaciation. In the Americas the comparable stage, the Paleo-Indian, began at least 12,000 years ago with the migration of people across the Bering Strait from Siberia.

In both continents culture based on hunting and gathering reached its peak of development during this period. Hunters became more expert, devising sophisticated techniques that involved large numbers of people working in cooperation to kill whole herds of game. In areas such as west and central Europe, where game was most plentiful, permanent communities sprang up, and the population rose in numbers and density. Besides the stone blade, which could be fashioned into any one of a variety of handy small tools, technical innovations included tools made of bone and ivory, clothing sewn together and decorated with beads, and among some groups a system of reckoning time by the Sun and Moon.

Among the finest productions of the Upper Paleolithic are the paintings and engravings (mostly animal representations) executed on stone slabs or ivory or on the walls of caves. The quality of this art is such that for many years critics refused to believe that it could be the work of prehistoric peoples. Even today, when its authenticity is established, its function is still obscure, but some of it is thought to have involved hunting magic or a ritual use. About 10,000 years ago the ice-sheets and tundra vegetation in the north gave way rapidly to coniferous and hardwood forest. The great herds of bison, horses, reindeer, and mammoths were replaced by more elusive, hard-to-hunt animals such as moose and elks. Human society and technology evolved in adaptation to the changing conditions. The resulting cultures are called Mesolithic in the Old World and Archaic in North America. New tools included microliths, tiny stone blades that were hafted in wood or antler handles. New weapons such as the bow and arrow enabled hunters to pursue the solitary game animals of the forest. Ingenious traps, snares, and nets enabled people to exploit resources such as wildfowl and fish that abounded in the lakes left by the retreating glaciers. Settlements became smaller, more dispersed, and less permanent .

In some areas humans adapted in a markedly different way to the end of the glaciation. Rather than diversifying their use of resources, as the Mesolithic people of the northern woodlands were doing, they focused their attention on a few reliable resources. The land to the east of the Mediterranean was one such area with evidence of this new orientation. There some populations began to concentrate on exploiting wild sheep and goats and a few species of wild grasses that produced edible seeds. Gradually, as revealed in the archaeological record, a mutual dependence developed between the human populations and the animals and plants they exploited and protected. The favored species, breeding under human protection, became modified so that they could not have survived without it. The humans, in turn, living in permanent settlements near the resources they exploited and tended, could not easily revert to nomadic hunting. The people had become farmers, and the animals and plants, domesticates.

Western Asia is the best-known, and perhaps the earliest, center of domestication, but several other early centers existed in various parts of the world. In Mexico an agriculture was developed on the basis of maize, beans, and squash. Other less-well-known centers of plant and animal domestication existed in Southeast Asia, China, and probably tropical Africa. In areas adjacent to some of these centers food production spread as hunters were displaced by farmers or acquired domesticates from their neighbors.

Contrary to a common notion, prehistoric villagers did not live more easily than hunters. Villagers tended to eat a poorer diet, work harder, and suffer from more diseases. However, they also tended to produce more offspring and thus built up a much denser population. Moreover, primitive agriculture and herding often exhausted the soil in a few seasons, forcing the early farmers to move on and wrest new territory from the hunters. So powerful was this process that within a few thousand years most hunting and gathering peoples had been replaced by cultivators or herders in all continents except Australia.

Along with their tendency to expand, food-producing societies are distinguished from hunter-gatherer societies by their emphasis on property. A hunter's principal assets are his weapon kit and his acquired skills. A farmer, by contrast, owns wealth in the form of land, herds, and the right to call on the labor of his friends and kinfolk. If he is lucky in these respects, or skillful in their management, he can both accumulate wealth and use it to buy the labor of others. By passing his wealth to his heirs, he can create a family of hereditary "notables" or headmen. In this way a stratified society emerges. Unmistakable indications of social stratification appeared within a few thousand years of the beginnings of agriculture. Within a few centuries more the process had culminated, in a few favored centers, in the appearance of complex societies in which specialist artisans and merchants plied their trades, a priestly elite presided over religious ceremonials, and a bureaucratic organization commanded the labor of the landless. And so, with the appearance of civilization, ended two million years of human prehistory.

The story of primate evolution begins about 80 million years ago, during the age of dinosaurs. Scurrying about in the trees at this time was an inconspicuous, insect-eating mammal the size of your first. This creature had big eyes and tiny, sharp teeth. Biologists think these ancient mammals were the ancestors of the first primates, the mammalian group that includes prosimians, monkeys, apes, and humans.

The first primates evolved about 60,000,000 years ago. Evolution favored two distinct anatomical changes that made promates better than their ancestors at stalking and capturing insect prey in the branches of trees.

1. One change was the development of grasping fingers and toes. The fingers and toes are tipped with nails, not claws. Unlike the clawed, unbendable toes of their ancestors, primates have grasping hands and feet that let them grip limbs, hang from branches, seize food, cling to their mothers when they are young, and, significantly, use tools.
2. The second change was in their position of the eyes in promates. The eyes of their ancestors were located on the sides of the head so that their two field of vision did not overlap. The eyes of promates are shifted forward to the front of the face. This forward placement of the eyes produces overlapping "binocular vision" that enables the primate brain to judge distance more precisely.

Judging distance accurately is a very important ability for an animal that leaps from branch to branch high above the ground. Other mammals have binocular vision, but only primates have both binocular vision and grasping hands. Three-dimensional sight and the ability to manipulate objects have played central roles in directing the evolution of increased intelligence in primates.

Hominid fossil skulls from about 35,000 years ago were first found in caves in southwestern France in 1868. Since then the fossil remains of these people, referred to as Cro-Magnon’s, have been found elsewhere in Europe as well as in Africa, Asia, and even Australia. Cro-Magnon’s had a cranial of about 1,400 cm3. They are distinguished from Neanderthals by their high forehead, prominent chin, and lack of brow ridges. Taller than Neanderthals, they stood about 1.8 m, or almost 6 feet, tall. Cro-Magnon’s were H. sapiens and are regarded by scientists as modern humans.

Cro-Magnon’s had a sophisticated culture. They made many types of tools, including a wide variety of blades, harpoons, scrapers, and even drills, fishhooks, and needles. They decorated the walls of caves with colorful paintings of the animals they hunted.

Paleoanthropologists differ in their interpretations of how humans evolved. This is because scientific theories are based on the based on the best available evidence and hominid fossil evidence is fragmentary.

There are many disagreements between scientists. The science of human evolution is an ongoing process. Precise observation and analysis of new evidence and reevaluation of theories will present more accurate and detailed picture of human evolution and I believe that the theory of human evolution might change in the future as new fossils are discovered.