The second argument is that the Green Revolution has decreased the "biodiversity" of crops in the world today. For example, before the

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revolution, it is speculated that there were over 30,000 different variants of rice that could be planted. Critics estimate that only ten modified rice variants are being used to grow for food. As a result, critics argue that if climate change, disease, or a rise in pestilence attacked the crops, famines may take place which may endanger certain populations.
The reason biodiversity is so important is because if one variant fails to a disease or pestilence, another variant can be used to counterbalance this event. If only a handful of variants are used, they could potentially be eliminated resulting in famines that could wipe out large populations. For example, if a trusted wheat variant has survived various diseases and has stood the test of time, it can be used to replace a variant that is not fairing so well, however if there is no such substitute, nations may risk putting all of their crops in one basket--and this may be disastrous.