At the end of the Pleistocene (around 10,000 B.C.), the technologies of food production may have already been employed on the fringes of the rain forests of western and central Africa, where the common use of such root plants as the African yam led people to recognize the advantages of growing their own food. The yam can easily be resprouted if the top is replanted. This primitive form of "vegeculture" (cultivation of root and tree crops) may have been the economic tradition onto which the cultivation of summer rainfall cereal crops was grafted as it came into use south of the grassland areas on the Sahara's southern borders.
As the Sahara dried up after 5000 B.C., pastoral peoples (cattle herders) moved southward along major watercourses into the savanna belt of West Africa and the Sudan. By 3000 B.C., just as ancient Egyptian civilization was coming into being along the Nile, they had settled in the heart of the East African highlands far to the south. The East African highlands are ideal cattle country and the home today of such famous cattle-herding peoples as the Masai. The highlands were inhabited by hunter-gatherers living around mountains near the plains until about 3300 B.C., when the first cattle herders appeared. These cattle people may have moved between fixed settlements during the wet and dry seasons, living off hunting in the dry months and their own livestock and agriculture during the rains.
As was the case elsewhere, cattle were demanding animals in Africa. They required water at least every 24 hours and large tracts of grazing grass if herds of any size were to be maintained. The secret was the careful selection of grazing land, especially in environments where seasonal rainfall led to marked differences in graze quality throughout the year. Even modest cattle herds required plenty of land and considerable mobility. To acquire such land often required moving herds considerable distances, even from summer to winter pastures. At the same time, the cattle owners had to graze their stock in tsetse-fly-free areas The only protection against human and animal sleeping sickness, a disease carried by the tsetse fly, was to avoid settling or farming such areas - a constraint severely limiting the movements of cattle-owning farmers in eastern and central Africa. As a result, small cattle herds spread south rapidly in areas where they could be grazed. Long before cereal agriculture took hold far south of the Sahara, some hunter-gatherer groups in the savanna woodlands of eastern and southern Africa may have acquired cattle, and perhaps other domesticated animals, by gift exchange or through raids on herding neighbors.
Contrary to popular belief: there is no such phenomenon as "pure" pastoralists, a society that subsists on its herds alone. The Saharan herders who moved southward to escape drought were almost certainly also cultivating sorghum, millet; and other tropical rainfall crops. By 1500 B.C., cereal agriculture was widespread throughout the savanna belt south of the Sahara. Small farming communities dotted the grasslands and forest margins of eastern West Africa, all of them depending on what is called shifting agriculture. This form of agriculture involved clearing woodland, burning the felled brush over the cleared plot, mixing the ash into the soil, and then cultivating the prepared fields. After a few years, the soil was exhausted, so the farmer moved on, exploiting new woodland and leaving the abandoned fields to lie fallow. Shifting agriculture, often called slash-and-burn, was highly adaptive for savanna farmers without plows, for it allowed cereal farming with the minimal expenditure of energy.
The process of clearance and burning may have seemed haphazard to the uninformed eye, but it was not. Except in favored areas, such as regularly inundated floodplains: tropical Africa's soils were of only moderate to low fertility. The art of farming was careful soil selection, that is, knowing which soils were light and easily cultivable, could be readily turned with small hoes, and would maintain their fertility over several years' planting, for cereal crops rapidly remove nitrogen and other nutrients from the soil. Once it had taken hold: slash-and-burn agriculture expanded its frontiers rapidly as village after village took up new lands, moving forward so rapidly that one expert has estimated it took a mere two centuries to cover 2,000 kilometers from eastern to southern Africa.
在更新世末期(大约公元前10000年),食品生产的技术可能已经在非洲西部和中部的热带雨林的边缘地区使用,在那里非洲山药等根茎型植物的普遍使用,使人们认识到自己种植食物的好处。山药的顶部如果被再植的话,很容易再次发芽。这种原始形式的“蔬菜栽培”(块根植物和树本作物的种植)可能已经成为了一种经济传统,基于这种传统,夏季降水谷类作物的种植也采用嫁接的办法,这种种植技术已经在撒哈拉沙漠南部边界地区的草原南部被使用。 随着撒哈拉沙漠在公元前5000年之后干涸,游牧民族(牧民)向南沿着主要河道迁移到了西非和苏丹的热带草原地带。直到公元前3000年,正如埃及文明发源于尼罗河流域一样,这些游牧民族定居在了离南部很远的东非高原地区的中心。东非高原是理想的养牛场所,如今也是像马赛人(肯尼亚和坦桑尼亚的游牧狩猎民族)这样的有名的牧牛民族的家园。直到大约公元前3300年,第一批牧牛人出现时,高地上居住着狩猎采集者,他们居住在平原附近的山区。在旱季和雨季,这些放牧人可能在固定的定居点之间移动,在旱季他们过着打猎的生活,在雨季靠畜牧和种植为生。 和其他地方的情况一样,在非洲,牛是饲养起来很费劲的动物。如果要饲养各种规模的牛群的话,这些牛至少每24小时就需要喝一次水,而且需要大片的牧场。饲养的秘诀在于仔细挑选放牧场地,尤其是在季节性降雨会导致全年牧草质量有明显差异的环境中。即使是规模适中的牛群也需要大片的土地和相当大的可移动性。为了获得这样的土地,经常需要牛群移动相当远的距离,甚至是从夏季牧场移动到冬季牧场。同时,放牧人不得不让牲畜在有舌蝇出没的地带吃草。唯一能够保护人类和牲畜,不患上昏睡病(一种由舌蝇传播的疾病)的办法,就是避免在这些地区定居或者放牧——对非洲东部和中部地区的牧民来说,这个办法严重地限制了他们的迁移。结果是,小牛群迅速地向南部地区迁移,在那里人们可以放牧。在谷类农业占领最南部的撒哈拉沙漠之前,非洲东部和南部稀树草原地区的一些依靠狩猎和采集生活的人可能已经饲养了牛群和其他家养动物,他们将牲畜作为礼物交换,或者通过劫掠放牧的邻居,来获得这些牲畜。 和主流观点相反:没有所谓的“纯粹”的牧民,即只依靠牧群生存的社会。撒哈拉沙漠地区为了躲避干旱而向南迁移的牧民,几乎肯定的是他们也在种植高粱、小米和其他热带降雨作物。到公元前1500年,谷类作物已经广泛分布于整个撒哈拉沙漠南部的稀树草原带。小型农业社区遍布在草原和西非东部森林的边界处,这些小型农业社区都依赖于所谓的轮耕法。这种形式的农业包括清理林地,焚烧清理过的地块上的那些被砍倒的灌木丛,将灰烬混合在土壤中,然后在这些制备好的土地上耕种。几年后,土地耗尽了养分,于是农民们继续前进,开辟新的林地,让原来的荒地休耕。轮耕法,也被称为“刀耕火种”,高度适用于没有犁的稀树草原地区的农民,因为这种方法能够消耗最少的能量来种植谷类。 在不知情者的眼中,清除林地和燃烧林地的过程看似是随意的,但事实并非如此。除了在耕种条件较好的地区,比如经常被水淹没的河漫滩地区:热带非洲的土壤的肥力只在中等水平甚至肥力很低。农业的艺术就在于小心地选择土地,那就是说,知道哪些土壤是轻土壤,容易耕种,很容易用小锄头翻种,并且可以在经过几年的耕种之后,仍然保持它的肥力,因为谷类植物会迅速地消耗氮和土壤中其他的养分。一旦谷类植物被种植,刀耕火种的农业会迅速扩大其范围,就如同在新土地上出现一个又一个的村落一样,轮耕农业会迅速地发展,以至于一个专家估计它仅仅只用了两个世纪的时间,就覆盖了从非洲东部到南部2000公里范围的土地。
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