> Plenty of animals and plants alter their environment to the detriment of others. Definite case in point: photosynthesizing organisms (green plants, algae, et

> Plenty of animals and plants alter their environment to the detriment of others. Definite case in point: photosynthesizing organisms (green plants, algae, etc.) We know that the Earth had a large-scale anaerobic ecosystem before the advent of photosynthesis. While anaerobic organisms still exist, they're only found in very narrow niches. >99% of them were wiped out, root and branch, apparently killed off by rising oxygen levels (oxygen is a poison to them).