Are we a part of Nature, or apart from it? Both ways of thinking have utility, and both have consequences. It is a commonplace that, as one of a million or more species of animals, we are a part of the natural world, and dependent on Earth and her biosphere for our survival at every moment. We are also unique (if less so, with discovery of tool use and problem-solving in everything from chimps to crows, self-awareness in dolphins, and so on).
We often feel apart, I think--whatever our head tells us. As a species, we have neither a near link joining us to the "Great Chain of Being,"** nor an equally intelligent neighbor to relate to as equals, since we are the last surviving bud on the human twig of the great Tree of Life.
For me, pollution brings the difference between Man and Nature into sharp focus. Humans as separate from nature pollute when we add a substance to the environment that harms other living things. But of course natural processes also do this: the end-Permian "Great Dying"--most terrible of all mass extinctions--probably came about partly due to release of deadly hydrogen sulfide gas by microorganisms in an anoxic ocean. We had nothing to do with it, since neither mammals nor the earliest dinosaurs yet existed. And it seems nonsensical to call acid rain-producing sulfur dioxide "pollution" when it comes from a coal-fired power plant but not when it comes from a volcano.
On the other hand, calling our activities (by definition) "natural" risks absolving ourselves or at least diminishing our responsibility for our actions. And, though both volcanic eruptions and fossil fuel combustion release greenhouse gasses, only the latter can we can do something about.
That very ability to foresee consequences, and to judge actions right or wrong thereby places on us the onus to act rightly; it simply is not given to us to be another blind force of nature. And blindness that is willed is not blindness at all. There is, in fact, a difference between a species wiped out by the chance workings of natural processes and that same extinction carried out by aware humans. It is the difference between accidental death and murder--or at least manslaughter. Both may be grieved, but only one cries out for Justice.
No. Flawed though it is, the distinction between Man and Nature is still a useful one.
*Sorry. "Humanity" doesn't have the classical ring.
**A pre-Darwinian concept that links all life in a static chain from the simplest living things to the most sophisticated (i.e. us, of course). It survives tenaciously as fragments in popular imagination, even though obsolete for a century and a half. See scala naturae here.