Prehistory

Human origins

Humans evolved in Africa from great apes through the lineage of hominins, which arose 7–5 million years ago. The ability to walk on two legs emerged in early hominins after the split from chimpanzees, as an adaptation possibly associated with a shift from forest to savanna habitats. Hominins began to use rudimentary stone tools c. 3.3 million years ago, marking the advent of the Paleolithic era.

The genus Homo evolved from Australopithecus. The earliest record of Homo is the 2.8 million-year-old specimen LD 350-1 from Ethiopia, and the earliest named species is Homo habilis which evolved by 2.3 million years ago. The most important difference between Homo habilis and Australopithecus was a 50% increase in brain size. H. erectus evolved about 2 million years ago and was the first hominin species to leave Africa and disperse across Eurasia. Perhaps as early as 1.5 million years ago, but certainly by 250,000 years ago, hominins began to use fire for heat and cooking.

Beginning about 500,000 years ago, Homo diversified into many new species of archaic humans such as the Neanderthals in Europe, the Denisovans in Siberia, and the diminutive H. floresiensis in Indonesia. Human evolution was not a simple linear or branched progression but involved interbreeding between related species. Genomic research has shown that hybridization between substantially diverged lineages was common in human evolution. DNA evidence suggests that several genes of Neanderthal origin are present among all non-sub-Saharan African populations. Neanderthals and other hominins, such as Denisovans, may have contributed up to 6% of their genome to present-day non-sub-Saharan African humans.

Early humans

Homo sapiens emerged in Africa around 300,000 years ago from the species Homo heidelbergensis. Humans continued to develop over the succeeding millennia, and by 100,000 years ago, were using jewelry and ocher to adorn the body. By 50,000 years ago, they buried their dead, used projectile weapons, and engaged in seafaring. One of the most important changes (the date of which is unknown) was the development of syntactic language, which dramatically improved the human ability to communicate. Signs of early artistic expression can be found in the form of cave paintings and sculptures made from ivory, stone, and bone, implying a form of spirituality generally interpreted as animism or shamanism. The earliest known musical instruments besides the human voice are bone flutes from the Swabian Jura in Germany, dated around 40,000 years old. Paleolithic humans lived as hunter-gatherers and were generally nomadic.

Anatomically modern humans migrated out of Africa in multiple waves beginning 194,000–177,000 years ago. The dominant view among scholars is that the early waves of migration died out, and all modern non-Africans are descended from a single group that left Africa 70,000–50,000 years ago. H. sapiens proceeded to colonize all the continents and larger islands, arriving in Australia 65,000 years ago, Europe 45,000 years ago, and the Americas 21,000 years ago. These migrations occurred during the most recent Ice Age, when various temperate regions of today were inhospitable. Nevertheless, by the end of the Ice Age some 12,000 years ago, humans had colonized nearly all ice-free parts of the globe. Human expansion coincided with both the Quaternary extinction event and the Neanderthal extinction. These extinctions were probably caused by climate change, human activity, or a combination of the two.

Rise of agriculture

Beginning around 10,000 BCE, the Neolithic Revolution marked the development of agriculture, which fundamentally changed the human lifestyle. Agriculture began independently in different parts of the globe, and included a diverse range of taxa, in at least 11 separate centers of origin. Cereal crop cultivation and animal domestication had occurred in Mesopotamia by at least 8500 BCE in the form of wheat, barley, sheep, and goats. The Yangtze River Valley in China domesticated rice around 8000–7000 BCE; the Yellow River Valley may have cultivated millet by 7000 BCE. Pigs were the most important domesticated animal in early China. People in Africa's Sahara cultivated sorghum and several other crops between 8000 and 5000 BCE, while other agricultural centers arose in the Ethiopian Highlands and the West African rainforests. In the Indus River Valley, crops were cultivated by 7000 BCE and cattle were domesticated by 6500 BCE. In the Americas, squash was cultivated by at least 8500 BCE in South America, and domesticated arrowroot appeared in Central America by 7800 BCE. Potatoes were first cultivated in the Andes of South America, where the llama was also domesticated. It is likely that women played a central role in plant domestication throughout these developments.

Various explanations of the causes of the Neolithic Revolution have been proposed. Some theories identify population growth as the main factor, leading people to seek out new food sources. Others see population growth not as the cause but as the effect of the associated improvements in food supply. Further suggested factors include climate change, resource scarcity, and ideology. The transition to agriculture created food surpluses that could support people not directly engaged in food production, permitting far denser populations and the creation of the first cities and states.

Cities were centers of trade, manufacturing, and political power. They developed mutually beneficial relationships with the inhabitants of the surrounding countrysides, receiving agricultural products and providing manufactured goods and varying degrees of political control in return. Pastoral societies based on nomadic animal herding also developed, mostly in dry areas unsuited to plant cultivation, such as the Eurasian Steppe and the African Sahel. Conflict between nomadic herders and sedentary agriculturalists was frequent and became a recurring theme in world history.

Metalworking was first used in the creation of copper tools and ornaments around 6400 BCE. Gold and silver soon followed, primarily for use in ornaments. The first signs of bronze, an alloy of copper and tin, date to around 4500 BCE, but the alloy was not widely used until the 3rd millennium BCE.