Reading A Sand County Almanac, and earlier reading the companion essay collection, has put me in mind of the big question of ecology and environmentalism: is man part of the system of nature? It's easy to make an unhelpful answer to this question which is factually true but misleading when it comes time to make policy. The companion essays glanced at it, but never bit into it, even when talking about the ways that Aldo Leopold addressed it, which is a disappointment.
At one ridiculous extreme, there are people who not only refuse to eat meat, not only refuse to eat root vegetables and anything which didn't fall on its own from a plant, but who wear gauze to make sure they don't accidentally harm an insect by breathing it in. One wonders why they don't cripple their immune systems to prevent them from harming bacteria. But even more absurd than that is those who would prevent a lion from killing a gazelle.
At the other ridiculous extreme is those who say that, since the earth's history is littered with the bones of species now extinct, usually at the hands (claws?) of other species, then anything man does is fine since it's just evolution continuing to happen. Why is it different when we build a dam that destroys the last of some fish (and let's say it's a fish we don't eat or use in any way), than when some species of wolf finishes off the last of a species of rabbit?
Both of these are deliberately exaggerated extremes (and yet I've heard both used as actual arguments made in earnest). But if you get right down to it, the latter viewpoint has some factual basis: we are animals, we are part of the ecosystem, and if our evolutionary advantages let us outcompete a lot of species and kill them off for our own benefit, that's different only in quantity, not in kind, from many previous extinctions all the way back to when one replicating molecular structure caused another one to stop replicating. It's true, but it's not helpful when it comes to making policy.
The simplest answer to that viewpoint is the simply utilitarian or economic argument. When we extinctify species left and right, when we pollute water tables, when we wash soil into the sea, etc. we are not only harming other species, we are harming ourselves, often in ways we don't see right away. First, there are the practical ways: maybe that bird we just extinctified would have produced a cure for cancer, or will turn out to be a key check on a bug that will otherwise cause a plague, or is an essential part of a food chain that we're part of. Then there's the more poetic ways that A Sand County Almanac evokes so compellingly: maybe the world we create without that bird will be poorer in ways that speak only to the experiences of a person's life, the lessons they'll learn, the joys they'll feel.
But while a practical case like this, focusing on how our behavior might be bad for us, can be more than enough to steer how we set policy, it's brittle. It's far too susceptible to arguments that the benefit to us of destroying some part of our environment is more than that of preserving it.
Here's an oversimplified example to make the point. Suppose you own a stand of marketable timber, good trees that will produce valuable lumber wood, and that take 50 years to grow. Which makes more practical sense: strip-harvesting it, or harvesting it sustainably? A young person just discovering environmentalism will almost always say sustainable harvesting is more financially sensible in the long run and insist strip-harvesting is only done by those who are thinking in the short term. But even if you think in a time scale of a thousand years, strip-harvesting makes more financial sense. A 50 year growth rate corresponds to a non-compounding 2% interest on investment. If you strip-harvest and then put the revenue in a plain old bank account, you'll accrue more money every year than sustainable harvesting, and that's even if the stripped land's value is ignored. (Obviously, there are other investments easily obtained with far higher than 2% return rates, and then compounding makes an even bigger difference.) If you bet the entire justification for environmentalism on practicalities, you run a real risk of running into situations like this, where you suddenly find your tactic justifying exactly the opposite of what you intend.
So we need an ethical element to our consideration of environmentalism, but that means we have to address the question of whether man's obligations to the world of which he is a part are in some way fundamentally different from the obligations of every other part of that world. After all, the essential fact of how nature works it that every part of it does what's best for it, and any harmony or synergy that arises is entirely emergent. (That includes cooperative and altruistic behaviors; when a mother spends its own energy suckling her young, that's still a result of her genes seeking their own benefit, and the same analysis works for all other forms of altruistic behavior in nature. For more analysis of this conclusion, see The Selfish Gene.) So how can we ethically justify man, as a result of his respect for this system, defying its most fundamental truth, making himself its exception? Doesn't that go the opposite direction from the desireable goal of reminding us all that we are part of it and cannot escape that fact?
Some writers have proposed that because we are able to understand the system and our place in it, we suddenly have a new obligation towards it. Aldo Leopold flirts with this answer, and it's probably the best one we have, but it's still not very compelling to me. It reminds me of the conundrum of Christian missionary work, and has the same problems as its justifications. For instance, it implies that anyone who manages to remain ignorant of ecology can therefore be forgiven any sins made against it, so oblivion is just as ethically sound as correct behavior. Which leads to the even stickier idea of "potential to understand" and any way you go there you just replace one ethical dilemma with another.
The more common answer is that a difference in quantity, if large enough, becomes a difference of kind: to wit, since our ability to change our environment is so much greater than that of a wolf, bacterium, or dinosaur, at some "critical mass" of power, our ethical imperatives suddenly and fundamentally changed. Again, this only works if you don't look at it too closely. There's no way that this ethical imperative can have a "sliding scale", that it's okay for one species to do something because it's tiny and limited, but as species become bigger and able to make more impact on the world around them, they gradually inherit more obligation to do so responsibly. Should we expect army ants to spontaneously generate ethical considerations more than we expect butterflies to, and do we consider them unethical for not doing so?
As a point of philosophy (or perhaps it would better to say "of sophistry") I don't have a satisfactory answer. All I can do is make a hodgepodge of these (and similar) answers that do not withstand a rigorous logical dissection. But I feel certain there is one I just haven't put my hands around, and maybe that no one has quite worked out yet. (Most writers who talk on this subject aren't really trying: they're content to make arguments that aren't rigorously logical and unassailable, but are instead persuasive, which is a different thing, often more useful.) Sometimes I can almost glimpse it, but it always falls apart, or turns out to be something else.