Thoreau here is returning to one of his principal themes, which can be summarised as follows: humans need wildness in order to ensure their survival. Thoreau saw humans as being placed in a critical relationship with nature, yet the problem with humans is that their civilisation and society often seems to involve the destruction of the untamed wilderness of nature and its systematical ordering. In the beauty of wild nature, Thoreau saw the source of the human spirit of independence and self-reliance, which were necessary in order for humans to keep on surviving and growing as a species. Thus, as he argues here, the wildness of nature actually contains the secret of the preservation of the world.
Put in other words, the wildness of nature helps us to remind ourselves of how we have to be independent and self-reliant in order to survive in this world. The wildness of nature is a necessary antidote to the various evils of society which detracts from these important values and encourages us to grow soft as humans.
The Thoreau quote, “In Wildness is the preservation of the world,” does not appear in Walden. It’s a line in his essay, “Walking.” This is followed by several paragraphs outlining the benefits of natural wildness to humans. “Hope and the future for me are not in lawns and cultivated fields, not in towns and cities, but in the impervious and quaking swamps,” he writes. Although the term “biological diversity” or “biodiversity” was not coined until more than a century after Thoreau’s death, he seems to have unconsciously been drawn to -- and found important -- the most botanically diverse places in his hometown of Concord, Massachusetts.
The concept of wildness appears in Walden in the “Spring” chapter, as follows:
“Our village life would stagnate if it were not for the unexplored forests and meadows which surround it. We need the tonic of wildness -- to wade sometimes in marshes where the bittern and the meadow-hen lurk, and hear the booming of the snipe; to smell the whispering sedge where only some wilder and more solitary fowl builds her nest, and the mink crawls with its belly close to the ground. At the same time that we are earnest to explore and learn all things, we require that all things be mysterious and unexplorable, that land and sea be infinitely wild, unsurveyed and unfathomed by us because unfathomable. We can never have enough of nature.”
In this passage, he again brings up diversity, but with examples of birds and mammals. He also introduces an important dichotomy: We want to be able to know and name wild things, but we also want them to somehow stay wild and mysterious. Do you think we can we have it both ways?