But for the survival instinct which nearly all creatures have, {more species would have been extinct/extinguished from the earth}
用would have
“could+have+done”是虚拟语气，表示对过去事情的假设，意思是本来能够做某事而没有做。
“would+have+done”虚拟语气，表示对过去事情的假设，意思是“本来会做”。
would have
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用could have。
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