One of the comments that was inspired by my earlier post on the invasive gall wasps that are threatening some native Hawaiian plants raised a point that is worth responding to in detail, since it comes up fairly often both in arguments with anti-evolutionists and in discussions about the costs and benefits associated with conservation efforts:
“Big Bill” said: “And further, letting foreign people plants and animals in always increases diversity. Sure, some native peoples, plants, and animals will die out, but it’s not like they have any right to the land. There is no God-given title. If the native peoples, plants and animals cannot compete and survive, that is their fault. It’s Darwin in action.”
Bill's statement does capture a basic fact about the biological effects of invasive species: if the invasive species outcompetes the natives, resulting in the extinction of the native species, it is simply a case of natural selection. I cannot argue with that. There are some who might claim that situations involving invasives do not count, because the invasive arrived as the result of human intervention rather than "naturally". I dislike that argument, both because it ignores the fact that the effects would probably have been the same regardless of the mode of arrival and because it implies that humans aren't really part of nature.