Their predecessors, probably H. erectus, had migrated out of Africa “during a warm interglacial period,” between 130,000 and 80,000 years ago in the Near East, which was subsequently taken over by Neanderthals [8]. Paleo archaeologists are not certain exactly when, but once the opportunity opened up, probably because the climate mellowed a little, successive waves of migration took place, which was called the Great Expansion [8]. Not long before and then accompanying the earliest migrations – the newly established time table estimates that around 70,000 years ago, M. tuberculosis began to infect and cause TB in H. sapiens – initially in Africa, then in Eurasia [9].
Hunter-Gatherers
Most of human history, to the limits that are known, was inhabited by hunter-gatherers, foragers who survived by hunting and killing animals, both large and small, and eating whatever foods they could pick from trees, find in nests or ponds, dig up, or scavenge. Before becoming extinct, groups of H. erectus survived as hunter-gatherers for around 2 million years – far longer than H. sapiens relatively brief existence thus far [4]. Dwellings, mostly temporary, were built and caves were commonly used for shelter and refuge. H. sapiens started out as nomadic hunter-gatherers, but as described in the next section, Neolithic Demographic Revolution, began to settle down in a single location, growing plants and domesticating animals.
A global marker of both the wide distribution and creativity of early H. sapiens culture are examples of Stone Age cave art. First recognized in Spain and France, outstanding decorative paintings were later discovered in Indonesia, some as early as 25,000–40,000 years ago. Before H. neanderthalensis became extinct, they also contributed to cave art. Most early cave paintings depict everyday animals – but some infrequent ones, such as mammoths, lions, and rhinoceros – and stencils of cave men’s (and women’s?) fingers and hands. Far less frequent were simple representations of human beings, often stylized.
Life expectancy was undoubtedly short, one educated guess is 35 years or less, and human survival remained treacherous for millions of years. Violence was epidemic. Competition between and among groups of hunter-gatherers seeking food, mating rights, and places of refuge must have led to violence. Many, but by no means all, anthropologists seem to agree that at least H. sapiens, and possibly earlier hominids, possess innate, genetically programmed lethal violence. Experts debate whether chimpanzees, our closest living relatives, have a similar violent predisposition. Other authorities agree that killing by apes does occur but nearly always from ordinary attacks of aggression. In contrast, as living conditions improved during the end of the Pleistocene period, the prehistoric human population of hunter-gatherers enlarged during the Great Expansion as serial colonization may have caused hunting territory to become crowded; competition seems to have triggered a few episodes of organized killing of humans by humans, which have been documented as shown below.
Human warfare is rarely illustrated in cave art, but one painting in Caugnac, France, dated roughly 25,000 years ago shows a “wounded man” with 3 spears protruding from his back and upper thigh, perhaps depicting some sort of interpersonal violence [10]. More scenes of war and battles show up in the rock art of Arnhem Land, N.T., Australia, dated “as early as 10,000 years ago” [11]. Another “unique evidence of a warfare event among hunter-gatherers” was reported recently (2016) by Mirazon et al. [12] in the late Pleistocene-early Holocene period in Kenya, Africa, at an “estimated age of –9,500 to 10,500 years (ago).” These authors describe the remains of a “minimum of 27 individuals,” 10 of whose 12 skeletons were found to have serious traumatic, presumably lethal injuries; in addition, there was evidence of arrow wounds, and other signs of “deliberate violent trauma.” These examples of warfare among nomadic hunter-gatherers overlap the early origins of newly settled human groupings. (See also later section on Prehistory of warfare.)
Neolithic Demographic Revolution
Hunting and gathering kept ancient H. habilis and descendant humans alive and surviving for nearly all the 2 million-plus years of human’s total existence. But it all changed, rather rapidly during the Neolithic Demographic Revolution (or Transition): a major turning point in human history [13]. It all started roughly 10,000 years ago, when H. sapiens began to slowly change from their nomadic lifestyles and settle down permanently and start farming and taming animals. According to Diamond [14], “Plant and animal domestication is the most important development in the past 13,000 years of human history”; it started not long before the beginning of the Holocene epoch (current), about 11,700 years ago. At first, domestication was scant and spotty and took several thousand years to refine, but the outcome was revolutionary. Hunter-gatherers had to either switch roles or disappear, leaving a world that – although still fundamentally primitive – began to add social classes and technological power to a rapidly expanding sedentary population chiefly engaged in agriculture.
Plant and animal domestication occurred by trial and error, but received a boost from the auspicious climatic and environmental conditions of the Fertile Crescent, particularly Mesopotamia and Babylonia, and in parts of China, notably the Yangtze and Yellow River basins. But Diamond [14] believes that what counted most was that these locations greatly favored “those regions to which the most numerous and most valuable domesticable wild plants and animal species were native” – hence, locally handy and ready for exploitation. Starting around 8500 BC, resident planters and breeders of those “pioneer crops” formed the world’s earliest centers of settlement, agriculture, and food production and then went on to spread their talents and technology elsewhere; presumably, the founders also shared their “experienced” genes to their neighbors’ benefit.
In time, additional even more favorable climates than the Fertile Crescent and China were discovered – along with both new and already domesticated plants and animals – and rapidly spread to the remainder of Eurasia and parts of Africa. This progressive relocation identified east-west regions having similar temperate climatic conditions, lengths of daylight, and seasonal variations [15]. The similarities among different latitudes enhanced technological adaptation, such as irrigation and soil enrichment. Much slower spread of food production was observed in a north-south axis of Africa and another in the Americas, where hunter-gatherers and hybrid groups of semi-sedentary foragers remained active until superseded by arriving colonizers.
Rewards of Agriculture and Domestication: H. sapiens’ remarkable conversion to a settled agriculture-based emphasis on farming and food production did indeed change human history forever, and in many ways. First of all, sedentary life permitted women to give birth roughly every 2 years rather than every 4 years, because once women settled down and changed to eating carbohydrate-rich diets, both their fecundity and fertility probably at least doubled, which greatly increased the population. A growing number of inhabitants generated new forms of specialized labor outside of agriculture and kindred activities, which spread to hierarchical administrative organizations, including royalty with leaders and pecking orders. These developments brought more and better goods and tools, the establishment of private property, and the development of individualized decision-making.
Downsides of Agriculture and Domestication: One little-known downside of the shift to agriculture and domestication includes the surprising fact that the nomadic life style of hunter-gatherers meant that they were physically larger and healthier than their sedentary, vitamin-deficient kinsman. Another liability, particularly in the early millenniums, was the increased prevalence of serious acute infectious