Thoreau had his simple dictum about basic necessity: one must maintain vital heat. Thus, in our ancestral native habitat (Equatorial Africa), this amounted to finding enough food through hunting and gathering. By the time Thoreau wrote Walden (and as many do not realize, he did not write this book at the Pond - the writing was done years later, based on notes which he kept while living in his one room house), the Little Ice Age in New England presented problems of a different order. Thus, maintaining vital heat required not only food but shelter and clothing.
I like this approach to the search for basic ideas, an Occam's Razor of ontology. If we were to state, a priori, the essential principles of human life beyond mere survival (Thoreau covered those correctly, I think), perhaps they can be stated as two axioms:
2. Existential insecurity.
Continuing in this Euclidean mode, we might be able then to derive from the axioms the basic theorems of existence.
One such derivation is this: it seems clear that human consciousness is maladaptive in evolutionary terms. Human cognition simply went too far. We may glory in our intellectual grandeur, but human intelligence has presented us with more problems than it has solved, and to make matters worse, it has presented us with problems of an insoluble nature. Another way of saying this is that intelligence somewhat superior to the chimpanzee and gorilla would have been sufficient to compensate for our evolutionary degradation in terms of size, strength and speed, but our development of intelligence overshot the mark and we wound up with nuclear fission, the internal combustion engine and the integrated circuit. These inventions are not necessary to maintain vital heat, but they do, paradoxically, practically guarantee our extinction.
Human consciousness and existential insecurity are interplaying elements. I was remarking to a friend at lunch on Monday that I regularly read a group of writers I call "the Apocalyptics," who, in this age of all graphs going parabolic, describe their ideas with a poorly-concealed lust for the imminent collapse of this monstrosity we call modern civilization, in favor of a return to a localized, comprehensible, anodyne world where we have a sense of control. Such writers include Richard Heinberg, Dmitry Orlov James Kunstler and many others, and whenever these highly intelligent, deeply insightful people are confronted, for example, with news that the United States might be able to convert its huge motor pool from gasoline to liquid natural gas and keep the whole car fiesta going for another one hundred years, these worthies lapse into paroxysms of outrage and scorn, denying that such a thing is possible.
Yet it is possible, unfortunately, and I suspect they know it. Indeed, it will probably happen. But you see, the Apocalyptics were counting on Peak Oil to act as the cavalry saving mankind (and particularly America) from itself. We needed something out of our control to make us do the right thing.
This last sentence begs a question: why is that? Simply put, it is because of our fundamental existential insecurity: at some point, after many years or a few, we all die. This is the essential reason that we cannot succeed in getting the human race to react constructively to overpopulation, global warming or the threat of nuclear annihilation. These aren't our biggest problems. Death is. A very personal, individual death.
Thus, to derive the theorem of human impotence in the face of existential threats from the two axioms: human intelligence went so far beyond what was necessary for basic survival that it reached the point where it was not only capable of creating the conditions for its own extinction, it also comprehended the futility of human existence itself. Increasingly, the thrall in which our consciousness was held by comforting mythologies is giving way to this searing recognition. As if to say, yes, it's true that homo sapiens is in mortal peril, but we all gotta go sometime. That will be our epitaph and our legacy.