Why did this change occur? After all, humans had done nicely as hunter/gatherers for many millenia. When you think about it in depth, this is really a restatement of Yali's question.
Traditionally, members of agricultural cultures would have answered that it was because of the inherent superiority of their life style, citing:
The benefits of improved nutrition: Obviously members of today's agricultural societies have better nutrition than members of hunter/gatherer societies. Moral and cultural superiority of agriculturalists. Indeed, in the early history of our republic, the failure of Native Americans to do anything "productive" with their land (i.e. to farm it the way Europeans would) was a primary legal basis for not acknowledging their ownership of it. (Consider the Supreme Court's ruling on the issue of Native American title to the land they inhabit.
- "But the tribes of Indians inhabiting this country were fierce savages, whose occupation was war, and whose subsistence was drawn chiefly from the forest. To leave them in possession of their country, was to leave the country a wilderness..." (Chief Justice John Marshall, 1823)
Diamond provides an alternate view based on the synthesis of anthropological, archeological, and historical data that suggests something more complex has happened.
Origins of Agriculture: Advantages of the hunter-gatherer life:
Summed up in one word: Health. Typically, ancient populations shifting from hunting-gathering to food production lost an average of six inches of stature and developed diet-related diseases including tooth decay.
Advantages of food production:
- Manure for fertilizer
- Animal muscle strength for plowing.
- Chieftans and kings
- Priests
- Specialist craftsmen
- Scribes and Bureaucrats
- Soldiers
- Increased human fecundity: Hunter-gatherers must carry their children with them when shifting camp. Thus, a woman may have no more than one child too small to keep up on its own. Between lactational amenorrhea, the effects of a low-carbohydrate "wild" diet, and other measures, births to hunter-gatherers are typically spaced about four years apart. Farmers, in contrast, can support as many children as they can feed, and a high-carbohydrate diet facilitates frequent pregnancies.
Concentration of useful biomass: Most plants (99.9 %) are "weeds" - useless to humans. To have enough useful ones, hunter gatherers must control large areas with diverse species. Farmers can simply turn a small area over to a monoculture of the plants they need.
Opportunity to domesticate livestock: Hunter-gatherers frequently move their camps. This eliminates the possibility of keeping large animals captive long enough to institute captive breeding. Farmers, in contrast, were responsible for major domestications of large herbivores. (Dogs, domesticated before the invention of agriculture, were a different story.)
Once livestock are domesticated their utility accelerates the development of plant cultivation:
Food storage: Hunter-gatherers have no effective means of long-term food storage. By favoring seed crops, farmers harvest the part of the plant that is capable of prolonged dormancy in the wild. Granaries give humans a buffer against unpredictable food shortages.
Division of labor: Once you have the ability to store food, it becomes possible to feed individuals who don't actual produce their own. Thus:
But the big one:
Cradles of Agriculture
- Definite independent centers of origin of agriculture:
The Fertile Crescent 8500 BCE Wheat, pea, olive China 7500 BCE Rice, millet Andes (and Amazonia?) 3500 BCE Potato, manioc Mesoamerica 3500 BCE Corn, beans, squash Eastern United States 2500 BCE Sunflower, goosefoot - Possible independent centers of origin of agriculture:
The Sahel 5000 BCE Sorghum, African rice Tropical West Africa 3000 BCE African yams, oil palm Ethiopia ?? BCE Coffee, teff New Guinea 7000 BCE Sugar cane, banana - Centers of secondary domestication of new crops after introduction of agriculture:
Indus Valley 7000 BCE Sesame, eggplant Western Europe 6000-3500 BCE Poppy, oat Egypt 6000 BCE sycamore fig, chufa
Diamond points out some paradoxes about the geography of the definite centers of origin:- Many, especially the Fertile Crescent, the Andes, and Mesoamerica are ecologically marginal
- Some of the world's most productive land, in places like Califormia, Eastern Australia, Argentina, and Southern Africa only began to be cultivated recently.
- Many available plants were not domesticated by local people. Wheat was domesticated in the Fertile crescent (right), but available in the Balkans, where it was ignored until agriculture was introduced as a package later.
The contrast is especially striking in the southwest US where, in harsh Arizona and the Colorado Plateau, agriculture was practiced for centuries next to the abundant environment of southern California (right), whose people remained hunter-gatherers.
Suggests that:
- Agriculture might have been more attractive in regions where:
- hunting and gathering was more difficult and less guarranteed of success
- a sufficient variety or abundance of domesticatable plants could be had to encourage success of transition.
- Hunter-gatherers in abundant environments may have observed the example of agriculturalists and said, "No thanks."
Plants to domesticate
Conscious, overt criteria for plant domestication:
- Size of fruit or seed.
- Mutations lacking bitterness or toxicity. Examples of almonds, lima beans, watermelons, potatoes, eggplants, cabbages.
- Fleshy or seedless fruit, oily seeds, long fibers
- Plants with short generation times
Unconscious criteria for plant domestication:
- Mutations that sabotage natural seed dipsersal mechanisms (non-shattering wheat heads)
- Mutations favoring rapid germination
- Mutations favoring self-compatible hermaphrodites
The Geography of domestication
Suitable plants aren't uniformly distributed. Indeed, although traditional agriculturalists have added many plants to our basic package, great efforts over the last two centuries have added very little that ancient people didn't already know about. Thus, we have a good inventory of domesticatable plants, so we can confidently say that:
- Most are from Eurasia.
- Indeed, Australia is especially bereft, having contributed only the macadamia nut.
- The Eastern US was not far behind, with early agriculturalists working with goosefoot, an allergenic relative of ragweed with tiny seeds. No surprise that this crop was abandoned when corn was introduced.
- The shape of continents effects distribution: Consider two basic facts:
- Similar latitudes tend to have similar climates
- Crops can easily be exported to regions with climates similar to those in which they were domesticated
- Taking them to regions with different climates requires the development of different varieties.
Domestication of large mammals
Again, certain traits predispose some animals to domestication and exclude others:
- Diet: We prefer herbivores, whose bodies capture more solar energy, and creatures with wide dietary ranges. Thus, lions and koalas are off our menu.
- Growth rate: We prefer fast growing livestock: Cattle are good, elephants bad in this light.
- Ease of captive breeding: We can't waste time on animals that won't reproduce on their own in captivity without heroic efforts on the part of their handlers.
- Tractability: We need animals that aren't too ornery. Horses are good, zebras, which bite and hold on and won't tolerate a saddle are bad.
- Tendency to panic: We prefer slower creatures that seek protection in herds or stand their ground, rather than running off like a shot. Thus, goats and sheep are good. Deer (except for reindeer) and pronghorns are bad.
- Natural dominance hierarchy: We prefer social creatures that naturally understand a dominance hierarchy that can be co-opted by human handlers.
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The winners:
- Sheep from Asian mouflon 8,000 ya
- Goat from west asian bezoar 8,000 ya
- Cow from eurasian aurochs 6,000 ya
- Pig from Eurasian wild boars 8,000 ya
- Horse from tarpan or Przewalski's horse of central Eurasia 10,000 ya
- Dog, possibly from wolf and possibly from extinct canids, 10,000 ya
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- Paedomorphic traits favored to promote tractability. Consider the half-century old effort in Russia to develop pet silver foxes. Tractable foxes have reduced production of adrenaline. Selecting for this requires selecting higher up on a biochemical cascade that also produce a cascading phenotypic effect that seems strangely familiar.
But domestic animals come with a down-side. Living in close association with them has provided a splendid evolutionary opportunity to their pathogens to colonize a new host: humans.
Pathogenic organisms that have made the jump to humans include:
- Measels from rinderpest in cattle
- Tuberculosis from cattle
- Smallpox from cattle
Each of these are examples of crowd diseases - diseases in which the pathogen takes advantage of host behavior and proximity for transmission. Of course, settled communities with high populations provide a selective pressure for such transmission that thinly-spread hunter-gatherer societies didn't.
When farmers and hunter-gatherers meet:
Such interactions aren't necessarily hostile. Indeed, cooperative arrangements based on division of labor can include:
- Cooperation between settled farmers and nomadic pastoralists. (E.G. traditional relationship of Hopis and Navajos.)
- Cooperation between settled farmers and forest specialists. (E.G. traditional relationship of Mbuti Pygmies of the Ituri Forest and their larger agriculturalist neighbors.)
So why do the non-agriculturalists always seem to disappear? When agriculturalists interact with their neighbors, they have certain advantages, regardless of their intentions:
- The ability to make more babies per unit of time.
- The ability to concentrate more people onto a given parcel of land.
- The inevitable tendency to transmit crowd diseases to their neighbors. NOTE: Typically an agricultural community will have some resistance to such diseases, either through childhood exposure or through evolved responses. Their hunter-gatherer neighbors will not. Thus:
Agriculturalists, who already had a population density advantage, will find themselves facing fewer and fewer hunter-gatherers because crowd diseases will kill more of them proportionally. E.G: English colonists in New England, including the "Pilgrims" had an easier time of it than they might, because they arrived after crowd disease plagues had decimated aboriginal populations. The town of Plymouth was built among the ruins of an evacuated Native American town.
All of this is despite the fact that, left on their own, hunter gatherers would typically be larger and healthier than farmers. Only two factors have altered this in recent times:
- The development of a global economy over the last 500 years, making crops from all over the world available to everyone, has enabled food-producing societies to overcome the shortcomings of the farmer's diet.
- The development of modern medicine, over the last 300 years, has enabled us to cope with those deleterious health effects.
A classic case study - the Bantu expansion
- Origins
- The Bantu language group is the largest single language group in Africa and includes familiar languages like Kiswahili and Isizulu. It is a member of the larger Niger-Congo group that originated in tropical West Africa.
- The Bantu group, itself, originated in northern Cameroon and Northwest Nigeria about 3000 years ago. At that time, they were in possession of African yams (a wet-climate, rainy summer adapted crop), sorghum, and cattle.
- Their expansion took them eastward, into regions occupied by pastoralists and southeast into the rain forests of the Congo Basin where they met forest hunter-gatherers (the ancestors of modern Pygmies).
- As they expanded, their languages fragmented and diversified.
- East African hiatus
- When they reached East Africa, they established themselves among pastoralists and dry-land farmers. With their wet-land adapted crops, they were able to farm land that the indigenous farmers couldn't manage.
- But East Africa had an established iron-working tradition, which the Bantus learned. Assimilating their own agricultural package with that of their neighbors, and picking up iron-working, the Bantus became highly competitive.
- Breakout
- But the problem: Their crops did poorly in the climate zones south of the Equator, so the Bantu expansion was halted. Southern Africa has no native plants suitable for domestication. It's native people, speakers of the Khoisan language group, were hunter-gatherers.
- Help arrived from the sea between 300 CE and 800 CE, when mariners from Indonesia arrived in Madagascar and East Africa. They colonized Madagascar successfully. In East Africa, they established trading relations, introducing bananas and Asian yams, which grow quite nicely in Southern Africa. Result: The Bantu expansion could continue southward.
- By the 1000 CE, the Bantus had engulfed the entire region from their Cameroonian homeland to the Fish River in South Africa's Cape Province. (The Fish River marks the boundary of the region in which Bantu crops thrived.)
- Bantu-Khoisan relations
- The Khoisan peoples are represented today by remnants including the San and Khoi peoples of southwest Africa. (The San were featured in the film The Gods Must Be Crazy.) Two local Khoisan languages are spoken in Tanzania - islands in the Bantu flood. Note: Khoisan people look physically dissimilar to people from farther north.
- Although Bantu languages and cultures prevail over southern Africa, there is linguistic and physical evidence that Khoisan peoples were assimilated by them:
- Remember the clicks? These originated in Khoisan languages but were taken up by many Southern African Bantus, including the ancestors of the Swazis, Zulus and Xhosas.
- Southern African Bantus often tend to have a Khoisan look about them. Clearly intermarriage took place.
Kenyan Nobel Laureate Wangari Maathai.
Nelson Mandela - Former President of South Africa
- Irony
- The Bantu expansion stopped before all of Southern Africa was engulfed because the Mediterranean (i.e. winter-rain) climate of the Cape and the deserts of Namibia and Botswana didn't suit their crops.
- The Cape climate suited European crops just fine. Thus, when Dutch settlers appeared in the 17th century, they became established on the continent without having to confront the Bantu nations directly.
- Regarding the Khoisans, the Dutch in the south treated them as the Bantus had in the north, engulfing, marginalizing, and marrying them. Their descendants: the "Coloreds" of South Africa.
- The Khoisan peoples are represented today by remnants including the San and Khoi peoples of southwest Africa. (The San were featured in the film The Gods Must Be Crazy.) Two local Khoisan languages are spoken in Tanzania - islands in the Bantu flood. Note: Khoisan people look physically dissimilar to people from farther north.
