Human being has the most highly developed brain of any animal. The human brain gives people many special abilities, the most outstanding of which is the ability to speak. Language has enabled human beings to develop culture, which consists of ways of behaving and thinking. These ways are passed on from generation to generation through learning. Culture also includes technology—that is, the tools and techniques invented by people to help satisfy their needs and desires. The richness and complexity of human culture distinguish human beings from all other animals.
The human brain helps make people the most adaptable of all creatures. They behave with the most flexibility and in the greatest variety of ways. The human body is highly adaptable because it has few specialized features that could limit its activities. In contrast, a seal has a body streamlined for swimming, but it has difficulty moving about on land. People cannot swim as well as a seal, but they can also walk, run, and climb. Human adaptability enables people to live in an extremely wide variety of environments—from the tropics to the Arctic.
People are inquisitive and have long sought to understand themselves and their place in the world. Throughout much of human existence, religion has helped provide such understanding. Nearly all societies have assumed that one or more gods influence their lives and are responsible for their existence. Since ancient times, philosophy (the study of truth and knowledge) has also provided definitions of what it means to be human.
Today, religion and philosophy remain important parts of people’s efforts to understand the nature of human existence. But many other fields of study also help human beings learn about themselves. For example, anthropology is the study of human cultures and of human physical and cultural development. Specialists in psychology study human and animal behavior and mental processes. Sociology deals with the groups and institutions that make up human societies, and history is the study of past human events.
This article describes the physical and cultural characteristics that distinguish human beings from other animals. It also traces human physical and cultural development. For more information on the life of early human beings, see Prehistoric people.
Characteristics of human beings
Scientific classification.
Biologists classify all living things in groups, including class, order, family, genus, and species. Human beings belong to the class of animals called mammals. There are about 4,500 species of living mammals, including such animals as cats, dogs, elephants, and otters. All mammals have a backbone, hair, four limbs, and a constant body temperature. Female mammals are the only animals with special glands that produce milk for feeding their young.
Human beings, along with apes, monkeys, lemurs, and tarsiers, make up the order of mammals called primates. Scientists classify human beings and apes together in the superfamily Hominoidea. Scientists have compared the anatomy and genome (the complete set of genes in an organism) of the African great apes with modern human beings. They determined that chimpanzees and gorillas are the closest living relatives to human beings. In fact, scientists have determined that about 98 percent of the genes of living people are identical to those of chimpanzees.
Within the Hominoidea, the subfamily Homininae includes human beings and their closest prehuman ancestors, gorillas, chimpanzees, and bonobos. A subdivision of this group called Hominini includes only humans and their extinct ancestors. Species in this group are often referred to as hominins. Human beings are the only living members of a genus called Homo, the Latin word for human being. This genus consists of one living species—Homo sapiens—and several extinct human species that are known only through fossil remains. The Latin words Homo sapiens mean wise human being. All existing peoples belong to the subspecies Homo sapiens sapiens.
Physical characteristics.
Human beings and the other primates share many physical features. For example, all primates rely on their excellent vision for much of their information about their environment. They have large eyes, sensitive retinas, and stereoscopic vision (the ability to perceive depth). Human beings and apes also have a highly developed nervous system and a large brain. Human beings and many other primates have long, flexible fingers and opposable thumbs, which can be placed opposite the fingers for grasping. In addition, their fingers and toes have nails instead of claws.
Many of the physical characteristics that distinguish human beings from other primates are related to the ability of people to stand upright and walk on two legs. This ability requires long, powerful legs. The human rump has strong muscles that propel the body forward and balance the trunk alternately on each leg when a person walks. In contrast, apes spend most of their time climbing and swinging in trees or walking on all four limbs. Their rumps have relatively weak muscles, and their arms are longer and stronger than their legs.
The human spine, unlike the spine of any other animal, has a curve in the lower back. This curve helps make upright posture possible by placing the body’s center of gravity directly over the pelvis. The human foot is also specially adapted for walking on two legs. Apes use all four limbs to support their weight, and they can grasp objects almost as well with their feet as with their hands. In human beings, however, the feet support the entire weight of the body, and the toes have little ability to grasp or to move independently.
The human brain is extremely well developed and at least twice as large as any ape’s brain. Because of the brain’s size, the human skull is rounder than any other primate’s skull.
Human beings live longer and develop more slowly than other primates. The human life span varies from an average of about 40 years in some countries to more than 70 years in most industrial nations. A human infant is born completely helpless and depends on its parents for many years. Most human beings reach full maturity only between 18 and 25 years of age. Slow growth and development allow for a much longer period of learning and brain growth than exists in any other species.
Cultural characteristics.
Some animals have simple aspects of culture. For example, young chimpanzees learn from older members of their group how to make some tools. They catch termites by peeling a twig and inserting it into a termite mound. They also chew leaves to make sponges for soaking up water to drink.
Certain animals, including apes and monkeys, communicate by making a wide variety of sounds. These sounds express emotion and may communicate simple messages, but they apparently do not symbolize any object or idea. Language distinguishes human culture from all forms of animal culture. Through elaborate use of symbols, language enables people to express complex ideas and to communicate about objects and events that are distant in time and place. By using language, human beings have developed the ability to reason and to solve problems on a far higher level than any other animal. Language also enables human beings to pass on knowledge and complex skills from generation to generation.
Human physical development
The Bible describes how God created the world and all its living things, including the first human beings, in six days. Many people accept this description as fact.
Evidence from fossils has convinced most scientists that human beings developed over millions of years from ancestors that were not completely human. But the fossil record does not yet provide enough information to trace human development in detail. As a result, not all experts agree on how human beings developed. This section describes human physical development as a majority of anthropologists believe it occurred.
Prehuman ancestors.
Anthropologists believe human beings, chimpanzees, and gorillas all developed from a common ancestor that lived between about 7 million and 10 million years ago. During this time, the ancestral population that leads to physically modern human beings diverged (split) from the populations that gave rise to modern gorillas and chimpanzees. This divergence represents the beginnings of the hominins. Because chimpanzees and gorillas are native to Africa and the earliest known hominin fossils are limited to Africa, scientists believe the human family originated there.
Anthropologists have discovered fossil remains of the earliest hominins at sites in Africa. The oldest known species, Sahelanthropus tchadensis << suh hehl AN throh puhs cha DEHN sihs, >> lived about 7 million years ago in what is now the central African nation of Chad. Another species, Orrorin tugenensis << aw RAWR ihn too guh NEHN sihs, >> is known from fragmentary fossil remains found in eastern Africa. This species lived about 6 million years ago. Two other species of early hominins are known from fossils that show a mixture of apelike and humanlike characteristics. These species, called Ardipithecus ramidus, lived in what is now Ethiopia in northeast Africa from about 5.8 million to about 4.4 million years ago. Like Orrorin and other hominins, Ardipithecus appears to have walked upright. However, fossil hunters have found only a small number of bones of these earliest hominins. Scientists know little about the biology of these creatures and their relationship to later hominins.
More than 4 million years ago, a more advanced form of humanlike creature called Australopithecus << aw `stray` loh PIHTH uh kuhs or `aw` struh loh PIHTH uh kuhs >> appeared in Africa. Anthropologists recognize at least six different species of Australopithecus from fossil remains. Members of the genus (group of species) Australopithecus are called australopithecines. Fossil remains of the australopithecine skeleton indicate that these creatures stood fully erect and walked on two legs. The australopithecines were about 31/2 to 5 feet (110 to 150 centimeters) tall. They had large, strongly developed jaws and large molars (back chewing teeth). These hominins had a brain about one-third the size of a modern human brain.
Early human beings.
Primitive human beings appeared about 2 million years ago in Africa. Anthropologists believe that these early human beings developed from the australopithecines. Fossil evidence suggests that by 1,800,000 years ago, several different species of early human beings lived in Africa. They are all placed in the same genus as living people, Homo. One species, Homo erectus (upright human being), had a larger brain and a more humanlike face and teeth than the other species. From the neck down, Homo erectus resembled human beings of today. But, like other species of early Homo, it had a large, projecting face and a low forehead with a large browridge, a raised strip of bone above the eyes.
Homo erectus made and used a variety of stone tools. About 1,800,000 years ago, these early people began to migrate out of Africa. Fossil sites indicate Homo erectus migrated to Asia and later to Europe. By 600,000 years ago, Homo erectus had migrated as far as northern China. The Chinese fossil sites show evidence that there Homo erectus made controlled use of fire and butchered large animals.
Human beings of today.
Scientists today are uncertain about precisely how physically modern human beings developed from earlier species of Homo. Some anthropologists suggest that modern human beings evolved directly from earlier Homo erectus populations who had spread from Africa through Europe and Asia. In this view, living people are the culmination of a long history in various geographic areas. For example, modern Asian peoples are seen as the descendants of the Homo erectus populations that reached Asia more than 1 million years ago.
Most anthropologists, however, support a different theory. This theory suggests that modern human beings are descendants of a single population of Homo sapiens that originated in Africa. Anthropologists who share this view cite genetic evidence that suggests Homo sapiens originated between 100,000 and 200,000 years ago. This population may have migrated from Africa, replacing populations of early human beings that existed in Africa, Europe, and Asia. Although scientists continue to debate the question of the exact origins of living people, genetic studies clearly indicate that all human beings today are closely related.
Human cultural development
Human culture has developed in three major phases. These phases have been based on (1) hunting and gathering societies, (2) agricultural societies, and (3) industrial societies.
Hunting and gathering societies.
For almost the entire prehistoric period of human existence, people lived by hunting game and gathering fruit, nuts, roots, seeds, and other plant foods. Evidence suggests that the hunters and gatherers lived in widely separated groups of 25 to 50 persons. These people roamed over large areas in search of food. They lived in harmony with their environment and used their natural resources efficiently.
The first inventions probably included weapons and cutting tools for butchering animals, plus containers for gathering plant foods. As people improved their hunting skills, they obtained big amounts of meat by killing large mammals, including elephants.
Agricultural societies became possible after people began to domesticate wild animals and plants about 10,000 years ago. These farming activities greatly increased the amount of food available in any area. Permanent villages appeared, and then towns and cities developed. The larger and more dependable supply of food supported a continually increasing population.
Agriculture made it unnecessary for everyone to help in the production of food. Some people became specialists in other fields, such as manufacturing or trade. Governments were established, and systems of writing were created. Thus, the invention of farming opened the way for the development of civilization.
Industrial societies
appeared in their modern form during the A.D. 1700’s, after people learned to run machinery with energy from coal and other fuels. Today, petroleum, coal, natural gas, and nuclear fuel furnish most of the energy used by industrial societies. These fuels have brought a great expansion of technology.
The processes and products developed by industry have greatly improved the standard of living for countless people. These developments have also helped make possible many other advances, including tremendous increases in human knowledge. But not all nations and economic classes have received the full benefits of industrial progress. Millions of people throughout the world continue to live without modern medicine, electric power, clean water, and sanitation. Industrial technology has produced many harmful side effects as well. Its wastes have polluted the environment, and its production methods have sometimes created monotonous, unfulfilling jobs.
