Yes, a change in environment does lead to evolution, as species adapt to those changes...incrementally, as those most suited to the changes evolve. Now ...as to the speed of these incremental changes...when evolution occurs, it occurs very rapidly..........in geologic time. In other words, while a species may remain on earth for a few million years, its evolution into a new species may take several thousand years. This is a blink of the eye in terms of geologic time.....but is nowhere near the amount of time to account for anything happening within the scope of human history. When environmental change occurs at a faster rate than species can evolve, extinction occurs....Since modern humans have evolved, our tendency to change the environment for our needs (a major human adaptation) has far outpaced the ability of other species to adapt and evolve....for example: despite evidence for prior arrivals, humans definitively entered the Americas about 13,000 years ago...with a talent for the use of fire as a hunting technique...the rich American megafauna of mammoths, mastodon, horses, ground sloths...extinct by 12,000 years ago. Now this is still disputed....there was also climate change...what is less disputed...Australia had a fantastically diverse biota...giant wombats...20 foot long monitor lizards....and not all that much desert. Humans arrived about 50,000 years ago. The megafauna of Australia was gone by about 40,000 years ago.....and the desert increased. The upshot? Change causes evolution. Evolution occurs quickly...in geologic time.....but still very slowly in human time. Yes, species do become extinct...its a part of the natural world. But to dismiss extinction that is a consequence of human activities is akin to dismissing a murder by saying that everyone dies eventually. Some of the species we care most about are probably not long for this earth, in geological time....face it, the giant panda is a beautiful and interesting animal.....and it has a wonderful adaptation for eating bamboo...unfortunately, if your only adaptation is for eating a tough woody grass that is full of silica, and that grass has a tendency to die after blooming...and blooms at the same time...well, you've had your turn on stage and its time for the next act. But pandas are cute...and we do all that we can to save it from what will be its eventual demise....while countless orchids, frogs, and who knows what else go to the eternal compost heap. Now...everybody loves pandas...and it is entirely appropriate to prevent their extinction as long as possible, not just because they are cute but because they have an intrinsic worth in their very existence..and only humans can appreciate an "intrinsic worth". But what about all the other organisms whose intrinsic worth is not appreciated by the bulk of humanity? We focus on species because it is easier to relate to them, rather than the whole nameless biota....but we have to face the reality that we have to preserve entire ecosystems in order to preserve the species. Yes, global warming can be a natural process....and yes, there were periods of global warming that occurred between glaciations ..and we had nothing to do with them. But when there is so much evidence that our return to the biosphere of carbon that had been sequestered for millions of years is ever more apparently contributing to an increase in global temperatures at a faster rate than had ever occured in geological time...and to dismiss it as just equivalent to the change that would naturally occur, is a denial of responsibility...Well, I've gone on too long...but it is Friday night...wine with dinner...you all understand. Take care, Eric Muehlbauer in Queens, NY...Cyps pubescens, kentuckiense, and Gisela all coming up while my Arisaemas and Trilliums bloom...along with an incredibly stinky Arum.........
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