Is the natural world that surrounds you the same as the one that surrounded your parents, or your grandparents? What about that of your great-grandparents?

The short answer, of course, is 'no.'

Fields that your parents might have run through as children these days are likely parking lots or crowded with buildings. The fishing hole they might have spent hot summer days cooling off in might also be gone. The animals your great-grandparents might have been aware of in the forests might exist only in books or zoos today.

And the same can be said of your great-grandparents: the natural world their great-grandparents knew likely also was much, much different than what they experienced.

But that's not to say you don't encounter "nature." It's just that the nature you're familiar with is not the same as that which past generations encountered. That's the message J.B. MacKinnon pushes through in his latest book, The Once and Future World: Nature As It Was, As It Is, As It Could Be.

He drives the point home with sobering statistics and tidbits:

* Coral reefs in the Caribbean "once were home to at least one and a half tons more fish per acre than they typically are today."

* The biomass off the East Coast of North America "may have declined by 97 percent since written records began."

* Seals once swam in the fresh waters of Lake Champlain in Vermont.

* "In the oceans, the world's biggest fish, from tuna to cod to swordfish to sharks, have been reduced to an estimated 10 percent of their past abundance."

Yet, in spite of these statistics, to a young child today the oceans are deep and full of life, the forests are haunted by predators, and well-stocked groceries evidence that we live in an abundantly productive world.

Reality is in the eye, and the age, of the beholder. Mr. MacKinnon further makes that point by recounting the fields he ran through as a young boy, the red fox that lived there, and how, years later, that "nameless grasslands" had been transformed into a housing subdivision.

Just about everyone on earth, I suspect, has their own version of this same story -- the childhood wilderness despoiled. For me, it was the beginning of a journey that would change the way I see the natural world. I came to realize that we, you and I, cannot hope to make sense of this thing we call nature by looking at what surrounds us, or even by seeking the wilderness. Instead, as science has begun to recognize, we need to reach back and revisit the past -- tens, hundreds, even thousands of years ago. What we find there is the living planet at its most extraordinary, often so far beyond what we know today that it challenges our expectations of what life on earth can be.

We -- you and me -- are, of course, a driver of these changes. We alter nature to suit our needs, whether that be clearing the forest to build homes or to farm or fishing the oceans to near-collapse for food and commerce. Our societies, through the burning of fossil fuels, clearing of forests, and forever paving over nature, are influencing the climate, and not always in the best of ways.

National parks have not been immune to such altering. In Yellowstone National Park wolves once were extirpated by hunters and trappers...before we realized that mistake and worked to return them. Wolverines in Glacier, North Cascades, Yellowstone, Grand Teton, and perhaps even Rocky Mountain are thought by some to need Endangered Species Act protection both because of humans literally encroaching on their habitats and because the warming climate is shrinking the snowfields crucial to their reproduction. Coral reefs within Virgin Islands National Park have been diminished by warming waters. Joshua trees could be pushed out of their namesake park by warming temperatures. Acid rain is altering the biology of streams in Great Smoky Mountains National Park. Sea-level rise predictions bode ill for Everglades National Park. The loss of glaciers in Glacier National Park will carry dire ramifications for watersheds, vegetation, and lifeforms that rely on them.

Battles -- and that's occasionally what they turn into -- to right this imbalance have led to the return of wolves to Yellowstone and Grand Teton, and have given piping plovers and five species of sea turtles a somewhat firmer toehold in Cape Hatteras National Seashore, though not without their critics. And yet there's an acceptance in some circles of the battles lost or not even entered.

People often say that only a disaster will convince us to change our ruinous relationship with the natural world, or that our grandchildren will curse us for the damaged planet we'll leave them. The history of nature suggests that neither statement is likely to prove true. Our own ancestors handed down a degraded globe, and we accepted that inheritance as the normal state of things. As our parents and grandparents did before us, we go about our lives in the midst of an ecological catastrophe that is well underway.

Catastrophe. You might say we are in a way sterilizing the planet of lifeforms that get in our way, or which we don't pay close enough attention to to realize how our behavior impacts them. 

"...we have largely eliminated the megafauna of our age. For at least 250 million years and through every variation in global climate, life on earth has not been so empty of large and fierce beasts as it is today except during periods of cataclysmic mass extinction," the author tells us. "The same is true of 'keystone species,' or the animals and plants with the greatest influence over the structure of their environments; no ordinary force in deep time has ever tended to erase them the way that humans have."

It's astonishing when you fully consider the impact of those statements. And when you realize such "erasures" are continuing today on land (the Florida panther), sea (through over-fishing and pollution), and the skies (Ivory-billed woodpeckers, Passenger pigeons, Blue-throated macaws, just to name a few examples).

Can we reverse these trends? Not wholly. Through our national parks we have created a string of open-air zoos that border on the edge of becoming biological islands. 

We talk of Yellowstone as home to the full complement of wildlife it bore before the national park designation was bestowed in 1872. And yet the park's elk, wolves, and bison cannot freely and naturally wander across the park boundaries without risk of being shot, wolverines are few in number, Canada lynx are rarely seen (though it's hard, if not impossible, to state the cats ever roamed the park lands in large numbers), non-native fish are crashing native trout populations, and warming stream waters in summer are endangering fisheries.

Wolves are missing from Rocky Mountain National Park, and in their absence the elk herds have ballooned, and led to culling by sharpshooters. Grizzly bears have been wiped clean from 98 percent of their original habitat in the Lower 48 states, and are not likely to reclaim it.

The list of wildlife threatened or endangered by humans goes on. Can we recover even a fraction of this vanishing nature. To do so requires, in part, finding a way to live comfortably with nature. And to give nature the space it needs.