Food varieties extinction is happening all over the world — and it is happening fast. For example, of the 7,000 apple varieties that were grown during the nineteenth century, fewer than a hundred remain. In the Philippines, thousands of varieties of rice once thrived; now only up to a hundred are grown there. In China, 90 percent of the wheat varieties cultivated just a century ago have disappeared.

Farmers in the past painstakingly bred and developed crops well suited to the peculiarities of their local climate and environment. In the recent past, our heavy dependence on a few high yielding varieties and technology-driven production and distribution of food is causing the dwindling of diversity in food crops. If some mutating crop disease or future climate change decimates the few crop plants we have come to depend on to feed our growing population, we might desperately need some of those varieties we have let go extinct.

Question: On the basis of the above passage, the following assumptions have been made:
1. Humans have been the main reason for the large scale extinction of plant species.
2. Consumption of food mainly from locally cultivated crops ensures crop diversity.
3. The present style of production, and distribution of food will finally lead to the problem of food scarcity in the near future.
4. Our food security may depend on our ability to preserve the locally cultivated varieties of crops.
Which of the above assumptions are valid?

The correct answer is 1 and 4.

Let us analyze the passage step-by-step to understand why assumptions 1 and 4 are valid, while assumptions 2 and 3 are not:

Analysis of Assumption 1: "Humans have been the main reason for the large scale extinction of plant species."
The passage directly links human agricultural systems to the rapid loss of food varieties. It states that "our heavy dependence on a few high yielding varieties and technology-driven production and distribution of food is causing the dwindling of diversity in food crops." This confirms that human-driven agricultural practices are the primary cause of the large-scale disappearance of crop varieties. Hence, Assumption 1 is a valid assumption.

Analysis of Assumption 4: "Our food security may depend on our ability to preserve the locally cultivated varieties of crops."
The text mentions that farmers in the past developed crops "well suited to the peculiarities of their local climate and environment." It warns that if a mutating disease or climate change decimates the few high-yielding varieties we currently rely on, we might "desperately need some of those varieties we have let go extinct." This implies that safeguarding our future food security depends on our ability to preserve and rely on these locally adapted, resilient varieties of crops. Hence, Assumption 4 is a valid assumption.

Why Assumptions 2 and 3 are invalid:
- Assumption 2 ("Consumption of food mainly from locally cultivated crops ensures crop diversity") is not supported by the passage. The text mentions that farmers painstakingly bred crops adapted to local climates, but it does not suggest that the act of consuming local food is the mechanism that ensures or restores crop diversity.
- Assumption 3 ("The present style of production, and distribution of food will finally lead to the problem of food scarcity in the near future") is too extreme. The passage warns of a risk under specific conditions (if a mutating disease or climate change strikes), but it does not claim or assume that the current system will inevitably result in food scarcity in the near future.

Therefore, only assumptions 1 and 4 are logically sound and valid based on the text.