Of all the remarkable inventions supplied to us by the United States over the past few hundred years, none is as valuable as the national park. "America's best idea" it is sometimes called, though that makes it sound calculated, like the Americans knew what they were doing.

In truth, when President Ulysses S. Grant signed a law creating Yellowstone National Park in 1872, the intention was simply to stop the area's "decorations" from being exploited. Surveyors had noted the geysers, hot springs and waterfalls; they acted to prevent predatory developers from noticing them, too.

Take a 360° tour of Yellowstone's Old Faithful below

It was only later that our modern conception of national parks came into focus. As the American frontier began to vanish, conquered all the way to the Californian coast, "thousands of tired, nerve-shaken, over-civilized people" began to realise, in the words of John Muir, that "going to the mountains is going home; that wilderness is a necessity; and that mountain parks and reservations are useful not only as fountains of timber and irrigating rivers, but as fountains of life".

Perhaps we take national parks for granted in Australia. It is easy to forget they may never have existed, that the land of Royal National Park, near Cronulla, might very well have folded into Sydney's suburban sprawl were it not for the foresight of Sir John Robertson, acting premier of NSW. Established in 1879, "the Nasho" is the world's second-oldest national park. We didn't come up with the idea, but, in fine Australian tradition, we were quick to pilfer it. And thank God we did.

Anybody who has ever walked the 26-kilometre coast track from Bundeena to Otford knows this is one of Sydney's best treasures, a sublime stretch of sandstone crags and lonely, surf-caressed beaches. Ignore the airplanes flying overhead and it's possible to sense what the area once looked like for the Dharawal people, before the rest of us arrived with our more aggressive ideas of what it means to live on the land.

Sometimes I try to imagine Australia without the national parks. This takes quite an effort, because there are more than 500 of them, covering something like 28 million hectares of land. I imagine what the country would look like without Kosciuszko, Mungo, Kakadu, the Flinders Ranges and the Great Barrier Reef (which is increasingly easy given recent developments). Impoverished, certainly.

We would not be able to resist consuming just one more cove, one more valley of the Blue Mountains. Our desire to live surrounded by beautiful things, to use every available resource for human enrichment, would ensure helter-skelter development until nothing much was left.

Here is what we would lose: places to walk, to picnic, to fish, to ride bicycles and horses; places to spend time with family and practise camping skills; places to be alone; places for native flora and fauna to flourish in peace. Sure, you might get space for a second airport. In exchange, you would lose all reserves of natural resources, biodiversity, and something for future generations to see and understand as the world without us. In short, you would lose perspective.

National parks are terrific reminders of our own compulsive greed. They highlight bad habits, too, and our easily forgotten fragility. Again, Yellowstone is a good example here: despite the hotels and highways, people are regularly killed by bears and other natural calamities. It has happened so often that the park historian, Lee H. Whittlesey, has written an entire book called Death in Yellowstone. "The Park is the untamed and unfenced wildlife and the amoral energy of thermal wonders," he says. "It cannot be treated lightly; when it is it erupts in death." In one memorable incident, a father puts his infant on the back of the bison, hoping to snap a family photo, only to be gored to death by its horns. You would think this kind of incident is enough to dissuade visitors from coming to Yellowstone, but the book is actually a bestseller. Perhaps this is because people love to amble up to the abyss and peer over, frightening themselves. National parks allow us to get close to the wildness we think we have tamed.

This reminds me of a trip I once made to one of the world's greatest nature reserves, the Masai Mara in Kenya. "Everything gets eaten here in the end," the guide told me, after we observed a leopard nursing a broken leg. It occurred to me later this was one of the allures of those deceptively open safari vehicles, and the low canvas tent I slept in, woken occasionally by hyenas prowling around outside. Visitors want to feel so close to the animals they are almost part of the food chain again. Call it prehistoric nostalgia.

Along with the national park, the US is also responsible for conceiving its more raucous sibling, the wilderness area. In 1924, the US Forest Service designated the Gila Wilderness in New Mexico at the urging of one of its foresters, Aldo Leopold. An avid outdoorsman, Leopold saw value in "a continuous stretch of country preserved in its natural state, open to lawful hunting and fishing, big enough to absorb a two weeks' pack trip, and kept devoid of roads, artificial trails, cottages, or other works of man". A national park could have hotels and caravan access; a wilderness was meant to remain untouched (excepting, of course, indigenous cultural uses). In 1964, congress passed the Wilderness Act, and now America has these areas all over the map. Australia has them, too, waiting out there for the truly intrepid: the South West Wilderness of Tasmania and the Lost World Wilderness Area on the NSW-Queensland border.

Unlike national parks, the rationale for wilderness has always been deliberately anti-economic. We have become so accustomed to perceiving land in terms of financial worth (its resources, its real estate) that sometimes we forget there are other abstract values. Wilderness puts these first, including biological and scientific worth. Wilderness areas protect biotic communities and genetic material we are only beginning to understand. They are crucial in the fight against climate change. Furthermore, wilderness is a "control" in the sense of showing how far this experiment of civilisation has taken us.

But perhaps the more interesting rationales for wilderness are the more controversial ones. Here I mean the conception of wilderness as a place of freedom, vital to original thought. In George Orwell's 1984, wilderness is outlawed by the totalitarian government for this very reason. Somebody wandering the wild moors might get notions in their head, conceiving a different order for the world. Leopold expressed this idea as "adventure" – one of his six necessities in life, along with work, love, food, air and sunshine. "It is because the vast majority of people do not have the courage to venture off the beaten path that they fail to find [adventure], and live lop-sided lives accordingly," he once told a group of students. Conformity is impossible in wilderness because there are no paths to follow except the one you make with your own two feet. By embracing adventure, you embrace your full potential.

Leopold threw one other reason into the wilderness debate, too. What is the point of worrying so much about preserving American institutions, he argued, "without giving so much as a thought to preserving the environment which produced them and which may now be one of our effective means of keeping them alive?". In other words, America was a country forged by its frontier, so why not keep pieces of the frontier alive in perpetuity? Many of the characteristics Americans like to imagine make up their national character – inquisitiveness, practicality, individualism, exuberance – came from their early engagement with the wilderness of the New World. Losing that wilderness threatened everything it produced.

Before we fob this off as hysterical romanticism, here is our own NSW Office of Environment and Heritage explaining the reasoning behind protecting wilderness areas for travellers and citizens in our own country: "Wilderness is part of our national identity. The 'bush' and the 'outback', landscapes so typified by wilderness, continue to hold a central place in Australian culture."

It is really not such a shocking idea when you stop to think about it. Asked to explain the essence of Australia – the specific "Australianness" that sets us apart from the rest of the world – people will often hold up jars of Vegemite or a pair of flip flops. But then they inevitably talk about mateship, and egalitarianism, and resilience in the face of hardship. They talk about Anzac, forgetting that something made the diggers, before they got on the boats. In truth, all of these Australian traits evolved, Darwinian-like, in relation to the wild places that our national parks and wilderness areas seek to protect.

So when I try that hypothetical, imagining Australia without its natural reserves, I inevitably hit a mental wall. Because without those places we are rootless, destined to become a different and less distinctive kind of people over time. We have national parks and wilderness areas because we need them; they are like photo albums, reminding us who we are.