Aristotle famously said 'Man is by nature a political animal.' This can also be translated as 'Man is an animal, the nature of which is to live in a city'. The point is that human beings are animals, as much as we like to forget it. At least, that is what I believe. I don't think that we have dominion over the animals, in the biblical phrase, although most of us act as if we do, whether we believe it or not.
Now, Thoreau sometimes seems to believe that humans are just animals, and elsewhere to believe that humans are only animals if they are insufficiently enlightened. Compare these quotes: "Man is an animal who more than any other can adapt himself to all climates and circumstances" sits uneasily alongside these: "We are conscious of an animal in us, which awakens in proportion as our higher nature slumbers." and "He is blessed who is assured that the animal is dying out in him day by day, and the divine being established."
Desmond Morris, in his book 'The Naked Ape', makes the point that to understand human nature, you do not need to observe so-called 'primitive' human beings - any human beings will do. If you wish to observe a lion, you seek out his habitat, and observe him. So with humans. The bulk of humans live in conglomerations of varying sizes. So that is where you should go to study them. If one lion in a thousand decided to live up a tree, you would not draw conclusions about lion behaviour from that one lion.
Just as it is in my cat's nature to walk in a circle a couple of times before lying down, it is in my nature to worry about my children, put on weight in my thirties, and, eventually, to develop an interest in gardening.
Thoreau sees nature as a well balanced and perfect system. But if HE were acting according to HIS nature, he would not be in the woods at all. He would holding down a job, fretting about his mortgage and trying to get his kids into one of the better schools.
Human nature seems to be killing the planet, so I am not above humanity changing its nature as quickly as it likes. But it is not particularly comforting to think that we have got ourselves into this mess by acting entirely according to a nature bred into us by millennia of evolution. And that the well balanced and perfect system of nature has brought us to this pass.
Perhaps the hardest thing for us to believe is that nature does not care whether we survive as a species, any more than any of the others which are now extinct. Deep down, somewhere, we are sure that we are special, and that our dominion is god-given.
And it seems also to be a part of our nature to think that we have no 'nature' at all, and in fact are acting according to impulses unique to ourselves. It is only by reflection and introspection that we can recognise our natures, and act according to a 'higher nature'. It is Thoreau's paradox that the well-balanced and perfect harmony of nature has to be denied in us in order for it to be preserved in general.