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Agricultural societies cannot exist without staple crops. Several food plants, such as kola and okra, are known to have been domesticated in western Africa, but they are all supplemental, not staple, foods. All the recorded staple crops grown in western Africa were introduced from elsewhere, beginning, at some unknown date, with rice and yams.

Therefore, discovering when rice and yams were introduced into western Africa would establish the earliest date at which agricultural societies could have arisen there.

Which of the following is an assumption on which the argument depends?

(A.) People in western Africa did not develop staple crops that they stopped cultivating once rice and yams were introduced.

(B.) There are no plants native to western Africa that, if domesticated, could serve as staple food crops.

(C.) Rice and yams were grown as staple crops by the earliest agricultural societies outside of western Africa.

(D.) Kola and okra are better suited to growing conditions in western Africa than domesticated rice and yams are.

(E.) Kola and okra were domesticated in western Africa before rice and yams were introduced there.

Solution

Passage Analysis

Agricultural societies cannot exist without staple crops.	The first statement says that Staple crops are necessary for the existence of agricultural societies.
Several food plants, such as kola and okra, are known to have been domesticated in western Africa, but they are all supplemental, not staple, foods.	This is a simple factual statement. It says that many food plants were known to have been domesticated in western Africa. However, none of these food plants were staple crops. All the food plants domesticated in western Africa are supplemental.
All the recorded staple crops grown in western Africa were introduced from elsewhere, beginning, at some unknown date, with rice and yams.	This is again a factual statement. It says that all the staple crops that were recorded to have been grown in western Africa were actually introduced from some other place. Records indicate that rice and yams are the first known staple crops to be introduced in western Africa. However, the exact date of this introduction is unknown.
Therefore, discovering when rice and yams were introduced into western Africa would establish the earliest date at which agricultural societies could have arisen there.	Based on the previous information, the author now concludes that finding out when rice and yams were introduced in western Africa will help in finding out the earliest date at which agricultural societies could have arisen.

Pre-thinking

The question stem asks us to find an assumption made by the author in the argument while he arrived at the conclusion. In other words, we need to find a piece of information which is not given in the argument but is still considered as true by the author.

Let us first look at the line of reasoning presented by the author. This will help us in prethinking some assumptions.

The author starts off by saying that “agricultural societies cannot exist without staple crops”.

He further presents two facts. He says that although many food crops were known to have been domesticated in western Africa, none of them are actually staple crops.

He also says that all the staple crops, so far recorded to have been grown in western Africa, were actually brought here from some other places and that the earliest known staple crops to be brought to Africa are rice and yams.

So the author concludes that knowing when rice and yams were brought to western Africa would help in establishing the earliest possible date when agricultural societies could have developed in western Africa.

So the author’s argument is as follows. All the records indicate that staple crops were first brought from somewhere else. Since staple crops are essential for the existence of agricultural societies, knowing when the first known staple crops were brought to Africa will help in knowing when agricultural societies might have arisen.

If you observe the entire line of reasoning, you’ll see that the author has been referring to the recorded staple crops or crops that are known to have grown in western Africa.

Let us now ask ourselves the following. What if the records do not capture the entire agricultural history of western Africa?

For example, the records could have captured the western African history only up to 1000 B.C. and no records are available for events before that date.

Then may be, there could have been other staple crops that were brought into western Africa many years before 1000 B.C. but later on abandoned because of some reason. In this case, knowing when rice and yams were introduced into western Africa won’t help establish the earliest date of the rise of agricultural societies.

Also, staple crops could have been developed in western Africa itself early on. Later on they could have been abandoned because of some reasons. Even if this were true, then knowing the date of introduction of rice and yams won’t help in establishing the earliest date of rise of agricultural societies.

Therefore either one of the above, if true, breaks the conclusion of the argument that “discovering when rice and yams were introduced into western Africa would establish the earliest date at which agricultural societies could have arisen there.”

So a couple of assumptions made by the author are:

1. No other staple crops were brought into western Africa, which were later on abandoned before the introduction of rice and yams.
2. Staple crops, which the records couldn’t indicate, were not developed in western Africa before the introduction of rice and yams.

With this understanding in mind, let us move on to the option choice analysis.

Analysis of option statements

People in western Africa did not develop staple crops that they stopped cultivating once rice and yams were introduced.	This actually seems to be a valid assumption because if other staple crops were actually developed before the introduction of rice and yams, then agricultural societies could have existed even before the introduction of rice and yarn. In such a case, knowing the introduction date of rice and yams might not help in establishing the date of rise of agricultural societies and this would, thus, break down the conclusion. So this option is a valid assumption in the argument and is the correct option.
There are no plants native to western Africa that, if domesticated, could serve as staple food crops.	We are not concerned about the plants that are present in western Africa and that could be domesticated into staple food crops. The argument is concerned only about whether or not knowing about the introduction date of rice and yams would help us in establishing the date of rise of agricultural societies. The mere presence of other crops currently in the region is irrelevant to the argument.
Rice and yams were grown as staple crops by the earliest agricultural societies outside of western Africa.	Whether rice and yams were grown as staple crops or supplement crops outside western Africa doesn’t really affect the argument. We were already given in the argument that rice and yams were staple crops in western Africa and that they were introduced from outside. Whether or not rice and yams were staple crops outside is irrelevant to the argument. So this is an irrelevant option.
Kola and okra are better suited to growing conditions in western Africa than domesticated rice and yams are.	The conclusion of the argument is that knowing the introduction date of rice and yams will help in establishing the earliest possible date of rise of agricultural societies.This option, however, doesn’t affect the conclusion. We are concerned about staple crops in the argument since agricultural societies cannot exist without staple crops. We are already given that kola and okra are not staple crops and so this option is irrelevant.
Kola and okra were domesticated in western Africa before rice and yams were introduced there.	We are concerned about staple crops in the argument since agricultural societies cannot exist without staple crops. We are already given that kola and okra are not staple crops and so this option is irrelevant.

–Solution created by Krishna Chaitanya