CHAPTER 15. THE PHYSICAL AND SOCIAL EVOLUTION OF HUMAN BEINGS
This chapter traces the evolution of man from the hominids (members of the Hominidae family with erect posture) to modern man. This process of evolution was much more than purely physical. It involved social evolution as well. Indeed, there would be no modern man if it were not for his social setting, for the process of evolution socially selected those traits that made man human. Those social traits of man-like creatures and man himself that aided both individual and group survival became naturally selected. The same type of social evolutionary processes also affected the non-human animals. Indeed, both animals and plants have much more complicated social interactions and communities than was ever contemplated just a mere two decades ago.
The study of the impact of social factors on evolution will go a long way to reveal which of man's characteristics are innate as opposed to those learned from social interaction with others. This effort will help delimit human nature itself and, thereby, avoid nebulous philosophical arguments as to whether, in an overall sense, humans are by nature good or bad.
Students of early man often act as if man did not have a biological past. They reason as if man had to develop every aspect of his society sui generis, without connection to his own animal ancestors, which certainly had social groupings. Man did not have to rationally calculate what type of society he wanted because society existed before humans. Human beings developed within societies and cultures. The biological perspective thereby adds crucial insights into the nature of humans. To a biologist the cultural patterns of human beings tend to appear highly homogeneous. The anthropologist sees an amazing array of human activity, whereas the biologist sees pattern commonalities.
The early Miocene period in eastern Africa was different from the Africa we know of today, which is dominated by bush and grasslands. The biome of the early Miocene was a continuation of the rainforests of the Congo Basin. The importance of plate tectonics for human beings now enters the picture. In the mid- Miocene the eastern African rift system developed. This created a series of elongated basins. Along the rivers and lakes of this area was a system of interconnected gallery forests. This provided a mixture of rain forest next to open areas. It is this change of habitats that gave rise to many primates that later developed into human-like beings (Tanner 1981:45-49). In the mid-Miocene, primates differed from both modern monkeys and modern apes. These creatures were able to take a variety of postures and get about in many different ways, including walking, running, galloping, leaping, climbing, reaching, and hanging. Some scientists have referred to these more human-like predecessors as "dryopithecids," which includes members of the genus Dryopithecus and Pliopithecus.
Fifteen million years ago there arose the first hominids or hominid-like creatures -- members of the genus Ramapithecus. Ramapithecus lived in Europe, Africa, and Asia. Members of this genus did not walk upright as hominids did. Nevertheless, Ramapithecus had the characteristic short and deep hominid face. In addition, its canine teeth were relatively small and its molars more human than ape-like.
Australopithecus arose anywhere from 6 to 3.7 million years ago. In 1977 at Laetoli, which lies south of Olduvai Gorge in northern Tanzania, archaeologist Mary Leakey and her group found fossilized footprints of Australopithecus. These footprints were of three hominids that had walked across a plain covered with a layer of volcanic ash from an eruption of Mount Sadiman. The ash was slightly wet from a light rain shower, and soft enough to leave clear outlines of the footprints of passing animals. The ash dried, hardening into a cement-like layer, thereby, perfectly preserving the impressions. These footprints are almost identical to modern man's. The big toe is short and close to the other toes, rather than long and separate from them as in the grasping feet of the non-human primates. In addition, as in modern human feet, there was a clear arch.
Just how or why man developed bipedal walking is still a mystery. Some say it was for protection. Standing upright would raise the level of the eyes and therefore extend the range of vision to locate predators at a greater distance. Others believe bipedalism developed because it freed the hands so that plant foods or tools could be carried. Clifford Jolly (197?) speculates that because early pre-men, were the largest primates depending on grain, a premium was set on the ability to manipulate objects of very small size relative to the hands. Thus, man became bipedal in order to pick up grass and other seeds.
As mentioned, the ability to walk upright freed human hands to use tools. Tool use then aided the species in the development of intelligence, for those who had the intelligence to effectively employ tools were the most likely to survive. Cooperation during hunting also provided a push for the development of intelligence, as the more cooperative hominids selectively survived. This increase in intelligence then created creatures who could more effectively wield weapons and other tools. In this way the activities reinforced each other in a feedback loop.
Language also played a significant role in the development of intelligence. Here was a very powerful tool indeed, perhaps the ultimate tool. Those more able to use language, and therefore to communicate, were more likely to survive. This obviously favored the development of further intelligence and cooperation.
In 1973 the American anthropologist Donald Johanson and a team of scientists from the United States, France, and Ethiopia dug in a number of sites collectively called Hadar, in the Afar area of Ethiopia. In 1974 they found a skeleton that was 40 percent complete and that dated to 3.4 to 3 million years ago. The structure of the hipbones suggests that it was a female. The finders nicknamed the specimen "Lucy". She was three and a half to four feet tall, and only weighed sixty pounds. Her legs, hips, and backbone were clearly adapted to bipedal walking. Lucy belongs to the species Australopithecus afarensis.
There are two other species of Australopithecus that camped near trees so they could quickly climb to safety or near rock faces that provided some protection from attack. Australopithecus africanus occupied much the same niche in which modern baboons now thrive. Gathered in social groups, they were basically opportunists eating not only roots and seeds, but also berries, nuts, grubs, beetles, small lizards, and birds' eggs. They used their hands with some agility, but were not adept tool-makers. The other species was Australopithecus boisei, a robust, stockier species about five feet tall with massive jaws. It originated about 1.75 million years ago.
Around 2.5 million years ago there arose a new species, Homo habilis, who most likely became the first maker of primitive tools in East Africa. Some paleontologists conjecture that Homo habilis descended from Australopithecus afarensis, while others insist the two lines had a common ancestor. Homo habilis was very similar physically to the Australopithecines. In size they compared roughly with Homo boisei, but they lacked the massive jaws and associated bony crest on their slightly bigger skull. One advantage Homo habilis enjoyed over their predecessors was their superior ability to walk. Australopithecus and Homo habilis were contemporaries, both living around 1.75 million years ago. The Australopithecines became extinct a million years ago.
The type of society developed by early humans is known as hunting and gathering societies. Undoubtedly, however, this type of society existed long before humans came on the scene.
Instead of eating the nuts, fruits, and grubs as they picked them, Homo habilis gathered the food and carried it away in crude containers woven from long leaves. This species was also more sociable than previous species, associating not only with family members but with non-kin as well. Moreover, they could make complex gestures and sounds that may be considered a rough language.
The existence of this more social human brings up the whole subject of social evolution within man. One of the social factors working to select cooperative males and bands of males was the degree of cooperation in the hunt. Human social development got a big boost when men cooperated enough to drive away from their kills large predators such as lions, hyenas, and other carnivores. And this very cooperation allowed man eventually to become the primary hunter, that is, the real "king" of the jungle.
Another important factor in social evolution was sexual selection. According to Fox (1972), the need for a high level of cooperation within the band led females to select those males who had shown hunting prowess, leadership, skill at tool making, and any other virtues contributing to the success of the family and the social group. Females also avoided males who were too aggressive. This type of sexual selection worked to produce more socially amenable offspring. As young males learned that females selected socially cooperative males, they became even more socially cooperative. For instance, they became less aggressive both sexually and toward others, trying more to fit in with the group rather than to become the group's leader. This behavior in turn reinforced the social stress on cooperation rather than conflict in mate selection.
Another group of social factors influencing evolution were those involving familial behavior. A factor favoring the socially cooperative male was that such a male would be around to protect the child and its mother. This favored the survival of those offspring with genes from socially cooperative fathers. These offspring in turn would be better fathers or mothers. Those males that stayed around also could teach their children survival skills. This would give their children a differential survival rate over those children with fathers who were less family oriented. Similar factors also apply to the mothers, but the crucial factor seems to be the selection of the more cooperative of the males.
The Pleistocene era was the time of the Ice Ages. This was also the period of the marked expansion of the human brain, sophisticated tool use, and the spread of hominids throughout the world. The change in climate produced by these ice advances had a marked effect on human evolution and the development of human culture. The gradual enlargement in brain size throughout this period probably reflects the increasing reliance on intelligence as an adaptive strategy.
Living about 1.5 million to 300,000 years ago was Homo erectus. This human had a skull that was long and low with a prominent brow ridge and a protruding jaw. His stance and general appearance is the same as Homo sapiens with the exception of being a little shorter in stature.
Homo erectus had a much larger braincase than H. habilis. Indeed, a steady trend in human evolution has been an increase in the size of the brain. The expansion of the brain is shown in the following figures: Australopithecus (400-500 cubic centimeters); Homo erectus (1000); Neanderthal (1400-1700); and Homo sapiens (900-2000) (Sagan 1977). But even more important than brain size was the internal reorganization that made possible new and better nerve networks and brain centers.
Homo erectus spread from Africa into the near east and then into Europe and Asia. They moved at a slow pace, probably no more than twenty to thirty miles in a generation. Around 1.4 million years ago Homo erectus mastered fire. Fire in turn provided the necessary warmth for this species to migrate into even colder climes.
Homo erectus made considerable progress in hunting. There is evidence of hunting for elephants and wild horses and the use of fire to drive animals into marshes. Some speech was probably necessary for this type of hunting, since it required considerable coordination. Despite this growing hunting skill, these people still consumed fruit, nuts, and roots as the mainstay of their diet.
Origin of Homo sapiens and Homo sapiens sapiens
Some 500,000 years ago the refinement to Homo sapiens occurred. It then took more than 300,000 years before modern man, Homo sapiens sapiens, emerged.
Based on DNA research Allan Wilson of the University of California maintained that Eve, the first modern female, originated in southern Africa about 140,000 years ago (cited in Fagan 1990). More traditional sources have always placed the date closer to 50,000 years ago. Either way, it may come as a surprise to some that modern humans originated in Africa and had black skin.
The arid wastes of the Sahara effectively sealed off modern man in sub-Saharan Africa for more than 80,000 years. However, because of improving weather conditions, between 128,000 and 90,000 years ago, modern humans moved across the Sahara to North Africa and the Nile Valley.
This movement of man out of Africa resulted in the creation of the different races of man as ecological conditions naturally selected different traits of men. This journey would also lead to the creation of other serious divisions, over which humans continue to fight.
Around 80,000 years ago there appeared in Europe and west Asia a sub-species of modern man, namely the Neanderthalers (Homo sapiens neanderthalis). Neanderthal-like people also lived in Iraq, China, and Israel. This type of man went into eclipse around 30,000 years ago.
Some 60,000 years ago the Neanderthalers buried a man in a cave in the Zagros Mountain highlands of Iraq. The body lay on a rough bedding of woven woody horsetails. Buried with the man were several different species of flowers. The flowers were arranged deliberately and did not simply topple into the grave. The flower species included yarrow, cornflowers, St. Barnaby's thistle, groundsel, grape hyacinths, woody horsetail, and a kind of mallow. Several of these flower species have until recently been used in local herbal medicine. Apparently, Neanderthal man had learned something about medicine, and was not quite the brute once commonly thought.
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