Humans

Humans, known in formal binomial nomenclature as Homo sapiens, are a primate species believed to have descended from early ape-like ancestors through the process of evolution. First described by Charles Darwin (1809–1882) in his 1859 book On the Origin of Species, evolution is the means by which the inherent traits of species change over time, resulting in improvements and new capabilities that enhance their ability to survive and thrive in their natural environments. While scientists continue to debate the exact origins and evolutionary pattern of Homo sapiens, the current consensus is that humans, in their present form, developed most of their definitive anatomical and cognitive characteristics approximately one hundred thousand to two hundred thousand years ago.

Homo sapiens are considered the most intelligent species on Earth and have a far more advanced capacity for communication than any other known form of life—two traits that led directly to the rise of human civilization. While the earliest undisputed evidence of advanced human society is approximately fifty thousand to one hundred thousand years old, the discovery and deployment of reliable agricultural techniques is cited widely as the foundational basis for modern civilization. Agriculture developed during a phase of human history known as the Neolithic Revolution, which began about twelve thousand years ago and significantly reduced the need for people to hunt and gather food, thus allowing culture to develop, flourish, and expand. Modern societies subsequently arose, slowly evolving over thousands of years into the global culture of the present.

The Origins of Humans

From a biological perspective, humans are most closely related to a group of species known as the "great apes," which includes chimpanzees, bonobos, and gorillas. Humans and the great apes share a common ancestor that lived approximately five million to eight million years ago but split along divergent evolutionary and genetic pathways for reasons scientists do not fully understand. The split resulted in the rise of about fifteen to twenty early protohuman species known as hominids. Again, however, much debate exists within the scientific community with regard to how many hominid species there were, how closely they were related, why some went extinct while others survived, which ones died out, and which ones continued to evolve into modern Homo sapiens.

About four million to five million years ago, hominids developed a bipedal gait, or the ability to walk on two legs, which is considered a watershed moment in the history of human evolution. About two million to three million years later, humans began to migrate out of Africa and populate other continents. The earliest human ancestors are believed to have arrived in Asia about two million years ago, with migration to Europe beginning about one million years later.

Homo sapiens are the direct descendants of a now-extinct hominid species known as Homo erectus. In addition to an upright posture, Homo erectus displayed a number of definitive anatomical characteristics seen in modern human beings, including similar bodily proportions, a larger skull and braincase, elongated legs, and relatively short arms. Homo erectus is also believed to have developed the first major advancements in stone tool technology, including hand-axes that facilitated significant manipulation of the natural environment.

Homo erectus first appeared approximately 1.89 million years ago and is thought to have died out about 143,000 years ago, giving way to Homo sapiens. During this phase of evolution, early humans developed advanced traits such as complex language, cultural multiplicity, the production of art, and the capacity for symbolic expression. These traits enabled early humans to form close interpersonal bonds and cooperate with one another as members of communities, which led to the development of more intricate societies.

However, Homo sapiens did not become the last surviving member of the genus Homo until much later; fossil evidence shows that Homo sapiens lived alongside another early human species, Homo neanderthalensis (commonly known as Neanderthals), for tens of thousands of years. Homo neanderthalensis went extinct approximately twelve thousand years ago, though researchers are not exactly sure why. Leading theories suggest that infectious diseases or major environmental changes led to their demise, but some scientists hypothesize that Homo sapiens may have intentionally killed them off.

Early Human Civilization

The extinction of Homo neanderthalensis roughly coincided with the beginning of the Neolithic Revolution, alternately known as the Agricultural Revolution. During the Neolithic Revolution, humans began to shift away from traditional hunting and gathering practices and move toward agriculture and the domestication of animals. Researchers have noted, however, that agriculture is actually more labor-intensive than hunting and gathering, which suggests that this was likely not a "revolution" in the strict sense of the term but rather a more gradual change. The effect of the Neolithic Revolution was immense, as it allowed humans to establish permanent settlements.

Like many aspects of human evolution and anthropology, the factors that facilitated the Neolithic Revolution are subject to debate. However, a general consensus within the scientific community is that the glacial retreat that marked the end of the last Ice Age likely played a major role. Glacial retreat commenced about twelve thousand to fourteen thousand years ago, leaving behind large expanses of arable land and resulting in climate changes that allowed humans to follow migrating big game animals to new locations in more northern latitudes. Anthropologists have noted that these animal migrations resulted in diminished game populations in the Middle East, which is where human agriculture and animal domestication are believed to have originated. This indicates that agrarian society may have developed more out of necessity than preference. Interestingly, scientists also have uncovered evidence that agriculture and animal domestication arose independently in other parts of the world in subsequent centuries, leading some to suggest that these advancements were inevitable byproducts of continued human development.

The earliest civilizations that lived in communities resembling cities developed in Mesopotamia, a region of the Middle East, approximately eight thousand years ago. In the ensuing centuries, a series of highly developed societies evolved in the region, leading the Middle East in general (and Mesopotamia in particular) to become known as "the cradle of civilization." A series of transformative developments took place between about 4500 BCE and 3000 BCE, including the invention of agricultural plows, the rise of bronze and copper metallurgy, the creation of the wheel, the emergence of written language, and the fabrication of clay-fired bricks. These advancements, in turn, led to the development of city-states, and by about 3000 BCE, the civilization of the ancient Egyptians had coalesced along the banks of the Nile River. The Egyptians achieved major breakthroughs in architecture, construction, mathematics, philosophy, art, and many other aspects of human culture. Their civilization is widely considered one of the most successful and important societies of the ancient world. Similarly, ancient Mesopotamia made seminal contributions to human development; in addition to developing the earliest known cities, Mesopotamian civilizations are believed to be the first to codify and institute systems of law. The best-known example of their legal systems is contained in the Code of Hammurabi, a script-covered stone tablet that dates to about 1750 BCE.

In addition to Mesopotamia and ancient Egypt, a third important ancient culture known as the Indus Valley Civilization flourished during this period. Maturing around 2600 BCE and persisting until about 1300 BCE, the Indus Valley Civilization featured intricate urban planning, as well as advanced water supply and drainage systems servicing a highly evolved population of laborers, traders, and artisans. Since its remains were not discovered until the nineteenth century, however, the Indus Valley Civilization has not enjoyed the same level of esteem as Mesopotamia or ancient Egypt.

While rice farming is known to have taken place in what is now China as early as 4000 BCE, it was not until about 2200 BCE that the advanced civilizations of ancient China developed. The timeline of ancient Chinese history is typically framed by the three successive dynasties that ruled the Yellow River Basin region from about 2200 BCE until 256 BCE. These dynasties, in order, were the Xia, the Shang, and the Zhou. The Shang dynasty is of particular interest to archeologists and historians, as extensive written records from the period have survived.

Major early European civilizations include ancient Greece and the Roman Empire. Ancient Greece flourished for much of the final millennium BCE and was composed of independent city-states, of which Athens and Sparta are the most well-known. The Spartans were among the most feared military powers of the ancient world, while ancient Athens is often said to be "the birthplace of democracy," since voting was commonly used as a tool of government and policymaking. The expansion of the Roman Empire precipitated the decline of ancient Greece, and the subsequent spread of Christianity across much of the civilized Western world marked the end of antiquity and the beginning of the modern age.

The Rise of Modern Humankind

The medieval period bridged the transition of antiquity into modernity and is typically said to have begun around 500 CE and lasted until about 1500 CE. While the broad-scale application of the term "medieval" is problematic, given that human societies were evolving and advancing in different ways and at different rates in various parts of the world, it does offer a useful means of understanding the definitive features of the civilizations that preceded the globalization of human culture.

During the medieval period, most civilizations functioned as kingdoms, with stratified social structures headed by an elite class of propertied individuals and led by a single ruler with largely autonomous authority. Kingdoms were a feature of societies throughout the developed world, including Europe, the Middle East, China, Japan, India, Mesoamerica, and many parts of Africa. However, traditional agrarian and hunter-gatherer societies persisted in isolated regions, including sub-Saharan Africa, North America, and Australia, among others. Modern concepts of nationhood largely arose from kingdom-based societal structures, given that kingdoms were traditionally composed of people who shared a common language and culture.

In the late fifteenth and early sixteenth centuries CE, European seafarers began to venture far beyond their homelands, exploring parts of the world that were not previously known to them. This began a phase of history known as colonialism, during which several European powers—led by Spain, France, Great Britain, the Netherlands, and Belgium—began to claim outlying territories as their own for the purposes of economic, political, and cultural expansion. The Industrial Revolution closely followed the age of colonial development, bringing with it the capacity for producing manufactured goods and the rise of privately accrued wealth and property. While timelines vary, most historians agree that the Industrial Revolution began around the middle of the eighteenth century CE and lasted until about 1840 CE, with a second phase of rapid economic and technological development known as the Second Industrial Revolution beginning around the middle of the nineteenth century and continuing until the outbreak of World War I in 1914 CE. Historians generally agree that the Industrial Revolution is the single most important event in modern human history; it led not only to major economic and political changes, including the rise of the free-market economy and the decline of monarchy, but also to metamorphic discoveries like electricity and developments such as the mass-scale production of manufactured goods.

Over the course of the twentieth century, continued economic development and the invention of modern communication technologies facilitated cross-cultural contact and the growth and proliferation of human society on an unprecedented scale. Contemporary human civilization remains diverse, with secular democracies coexisting alongside authoritarian dictatorships and theocratic regimes. Key issues facing humankind in the twenty-first century include environmental degradation, overpopulation, and challenges and conflicts related to resource control and management.

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