在以往的的托福阅读考试中有这样一道题：部落迁徙。针对这道托福考题，前程百利小编为大家普及一下相关背景知识，这样有助于考生在面对这类题目时方便作答。这篇文章有社会历史学的背景，希望大家可以了解相关托福阅读背景知识。
托福阅读真题：
版本一：讲某个部落的人迁徙到一个新的地方。他们即是游牧的，但又会种植作物。但是最后不得不迁徙，因为人太多了。wild animal和作物都不够吃。
版本二：climate对N族人的影响 他们开始更大范围的hunt 种grain之类的
相关背景材料：
Younger Dryas
Three temperature proxies showing the Younger Dryas event at around 12 ka BP. The NGRIP sequence (red – mislabelled as GRIP) uses the water molecule isotopic composition – δ18O. The Vostok and EPICA Dome C series show delta-deuterium. All 3 proxies use the same vertical axis.
The Younger Dryas stadial， also referred to as the Big Freeze was a geologically brief (1300 ± 70 years) period of cold climatic conditions and drought which occurred between approximately 12800 and 11500 years BP. The Younger Dryas stadial is thought to have been caused by the collapse of the North American ice sheets although rival theories have been proposed.
It followed the Bolling-Allerod interstadial (warm period) at the end of the Pleistocene and preceded the preboreal of the early Holocene. It is named after an indicator genus the alpine-tundra wildflower Dryas octopetala. In Ireland the period has been known as the Nahanagan Stadial while in the United Kingdom it has been called the Loch Lomond Stadial and most recently Greenland Stadial 1 (GS1). The Younger Dryas (GS1) is also a Blytt-Sernander climate period detected from layers in north European bog peat.
The Dryas stadials were cold periods which interrupted the warming trend since the Last Glacial Maximum 20000 years ago. The Older Dryas occurred approximately 1000 years before the Younger Dryas and lasted about 3000 years. The Oldest Dryas is dated between approximately 18000 and 15000 BP.
The Younger Dryas an intense cooling and drying event of global proportions has been attributed a major causal role in the adoption of agricultural economies in the southern Levant. Here the impact of the Younger Dryas on human adaptations is evaluated using a small game index that measures the efficiency of human foraging as a proxy for site occupation intensity. The study examines faunal assemblages spanning the agricultural transition and dating to the Early and Late Natufian and Pre-Pottery Neolithic periods (ca. 14500 to 11000 Cal. BP). The small game index and other supporting evidence document major fluctuations in human site occupation intensity across this critical phase. Site occupation reached an unprecedented high during the Early Natufian but quickly reverted to pre-Natufian levels with the onset of the Younger Dryas in the Late Natufian phase. By decreasing site occupation intensity and increasing mobility the Late Natufians implemented effective demographic strategies to cope with changing resource distributions. In contrast there is no evidence for intensified resource use or food stress in the Late Natufian at least in comparison to the Early Natufian phase. Although it is tempting to assign the Younger Dryas a causal role in the adoption of agricultural economies support for this hypothesis (in the form of food stress and resource intensification) does not currently exist.
Natufian culture
The Natufian culture was an Epipaleolithic culture that existed from 13000 to 9800 B.C. in the Levant a region in the Eastern Mediterranean. It was unusual in that it was sedentary or semi-sedentary before the introduction of agriculture. The Natufian communities are possibly the ancestors of the builders of the first Neolithic settlements of the region which may have been the earliest in the world. There is some evidence for the deliberate cultivation of cereals specifically rye by the Natufian culture at the Tell Abu Hureyra site the site for earliest evidence of agriculture in the world. Generally though Natufians made use of wild cereals. Animals hunted included gazelles.
The term "Natufian" was coined by Dorothy Garrod who studied the Shuqba cave in Wadi an-Natuf in the western Judean Mountains about halfway between Tel Aviv and Ramallah.
Remains of a wall of a Natufian house
Settlements occur in the woodland belt where oak and Pistacia species dominated. The underbrush of this open woodland was grass with high frequencies of grain. The high mountains of Lebanon and the Anti-Lebanon the steppe areas of the Negev desert in Israel and Sinai and the Syro-Arabian desert in the east were much less favoured for Natufian settlement presumably due to both their lower carrying capacity and the company of other groups of foragers who exploited this region.
The habitations of the Natufian are semi-subterranean often with a dry-stone foundation. The superstructure was probably made of brushwood. No traces of mudbrick have been found which became common in the following Pre-Pottery Neolithic A (PPNA). The round houses have a diameter between three and six meters and they contain a central round or subrectangular fireplace. In Ain Mallaha traces of postholes have been identified. "Villages" can cover over 1000 square meters. Smaller settlements have been interpreted by some researchers as camps. Traces of rebuilding in almost all excavated settlements seem to point to a frequent relocation indicating a temporary abandonment of the settlement. Settlements have been estimated to house 100–150 but there are three categories: small median and large ranging from 15 sq. m to 1000 sq. m of people. There are no definite indications of storage facilities.
Sedentism
A semi-sedentary life may have been made possible by abundant resources due to a favourable climate at the time with a culture living from hunting fishing and gathering including the use of wild cereals. Tools were available for making use of cereals: flint-bladed sickles for harvesting and mortars grinding stones and storage pits.
Development of agriculture
According to one theory it was a sudden change in climate the Younger Dryas event (ca. 10800 to 9500 BC) that inspired the development of agriculture. The Younger Dryas was a 1000-year-long interruption in the higher temperatures prevailing since the Last Glacial Maximum which produced a sudden drought in the Levant. This would have endangered the wild cereals which could no longer compete with dryland scrub but upon which the population had become dependent to sustain a relatively large sedentary population. By artificially clearing scrub and planting seeds obtained from elsewhere they began to practice agriculture. However this theory of the origin of agriculture is controversial in the scientific community.
以上就是今天的托福阅读材料，大家可以在练习托福阅读材料的同时，积累一些相关词汇及句型，以便考试的时候更好地把握文意，夺得托福阅读的高分。前程百利小编预祝大家托福考试取得优异成绩!
