Loss of biodiversity matters because it affects the overall sustainability of organisms in an ecosystem. It also affects how badly an ecosystem will be affected after something, maybe a natural disaster, or maybe a disease, strikes the region. (For example, if a disease affects a certain species of organism, if there was a lot of biodiversity among individuals, some will have some kind of natural immunity to that disease and survive, passing on their favorable traits to the next generation. However, if everybody was the same and did not have the immunity to that disease, that entire population would eventually die out.) <- This is also the reason that lack of biodiversity will inhibit natural selection.
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