As the Earth’s population surges toward the 7 billion mark, the following twist on an old maxim perhaps best applies: A single birth is a joyous occasion. A billion births is a tragedy.

When the planet’s human head count topped the 6 billion threshold in 1999, few pundits seemed to grasp the catastrophic ecological implications. Rush Limbaugh weighed in with frequent assurances that the entire global population could fit comfortably in the state of Texas. But as the planet endures an alarming net gain of more than 73 million a year, or some 200,000 people a day, it would be naïve to think that this explosion can occur without grave environmental repercussions.

Until now, there has been a dearth of literature linking human population growth and biodiversity loss. However, Jeffrey K. McKee’s stunning, albeit flawed, new book Sparing Nature pinpoints the precise moment (in geological terms) when our early ancestors’ success resulted in the death of neighboring species–roughly 1.8 million years ago, with the arrival of Homo erectus. Around that time, African mammals began to disappear at an unparalleled pace. But the biodiversity crisis really accelerated, McKee establishes, at the onset of the agriculture age, some 10,000 years ago, when humans enjoyed unprecedented growth. The book then takes the cause-effect model one step further and assesses what the mass decline of species diversification means for the continuity of the human race.

McKee, an anthropology professor at Ohio State University and co-author of The Riddled Chain: Chance, Coincidence, and Chaos in Human Evolution, offers several theses in Sparing Nature. He argues that preserving biodiversity is essential to the health of the planet, and consequently the long-term survival of the human species. On this point, he offers incontrovertible evidence. Mining the fossil record, McKee demonstrates that it is no coincidence that our impressive proliferation also corresponds with what many scientists believe is the planet’s sixth major period of mass extinction. And as history reveals, mass extinctions don’t bode well for the top of the food chain (just ask the victims of Mass Extinction No. 5–the dinosaurs).

Humans, McKee notes, have a long and troubling history of muscling out other species through a myriad of practices, including agriculture, irrigation, habitat destruction, pollution, the introduction of invasive species and our latest contribution–the dramatic and irresponsible overproduction of greenhouse gases. While tropical rainforests are cleared in order to make room for farms, McKee ruefully observes, the constant felling has generated a mere 13 percent of the world’s cropland, yet it has spelled disaster for disproportionately high numbers of flora and fauna. For example, of the known plant species worldwide, at least one in eight is threatened or hovers near the brink of extinction. To date, human activity has put 40-50 percent of the Earth’s available land out of commission to a vast number of species, which are critical to eco-stability. Furthermore, these lands have now been rendered worthless even to humans because of overfarming and excessive development.

Some may ask, so what if we lose a minor species here or there in the march of progress? To many, the loss of Northern California’s endangered tiger salamander (threatened by sprawl) would represent a far less significant loss than the annihilation of the mighty Bengal tiger (the public tends to respond more strongly to the large, majestic threatened animals). But McKee evinces that an absence, either large or small, in nature’s master blueprint has a ripple effect. “What is lost with one type of animal are the others that depend on it. What is lost is an ecosystem.”

With an elegant and earnest writing style more common among nature writers than academics, McKee tallies the value of a balanced ecosystem, explaining, “These complex systems took millions of years to evolve, and the resulting web of life is not easily unwoven. The extinction of one species may have dire consequences for its coevolutionary partners. Thus, in today’s highly evolved world, it takes biodiversity to sustain biodiversity.” It’s easy to spot other areas of life where varied components help complex entities survive and thrive, as diversity is considered good for college campuses, 401(k) portfolios and a healthy diet. Similarly, Sparing Nature confirms that biodiversity is integral to a healthy and robust planet, serving critical functions in everything from climate management to erosion control.

Despite its sobering analysis, Sparing Nature is perhaps a bit too damning in one of its main points: “The impact of our large population would be great even if we were to behave differently.” McKee follows up by stating that our mere presence–regardless of whether we recycle, drive a hybrid, support organic farming or eschew McDonald’s–will always limit or reduce biodiversity. In short, our behavioral choices have less impact than our sheer numbers. But this contention seems to fly in the face of logic. After all, not all humans leave a similar footprint on the ecological landscape. The United States, for example, is the most prolific global polluter, and thus habitat destroyer, in many categories, particularly the generation of greenhouse-gas emissions. Yet our population is dwarfed by both China’s and India’s. Contrary to McKee’s line of reasoning, a two-child family living in a 12,000-square-foot Westchester County home, which is heated, air-conditioned, landscaped and redecorated every two years with furniture made from Indonesian rainforest wood is having a greater impact on nature’s ability to function unimpeded than a family of eight living under one roof in a Mexican village.

In fact, a study published in a January issue of the journal Nature found that an increase in the number of homes sheltering fewer people is more damaging to the environment than simple population growth. This trend–in which a nuclear family of four lives in a separate home rather than with the traditional extended family–is uniquely congruous with Western prosperity. The study notes that the rise in the number of dwellings with fewer occupants leads to a greater exploitation of natural resources such as land, energy, wood and water, and that this amplified use of scarce reserves is endangering species diversification.

McKee does make a convincing argument about the greater number of mouths to feed. At first glance, his contention holds up, as food is perhaps mankind’s common denominator. Everyone needs sustenance, and man’s taming of the land in the quest for food has dealt the greatest blow to biodiversity. But not all mouths are equally demanding. As Lester Brown, one of the world’s most influential environmental thinkers, noted in his book Who Will Feed China?, if the Chinese diet mirrored the Japanese diet, all the world’s fish stocks would be depleted. Once again, affluence seems to be a more overriding variable than raw numbers.

As one of the regions of the country experiencing unprecedented population pressures, California offers a unique glimpse into how human behavior shapes the landscape in a more significant way than the sum of all people. Over the next twenty years, the Golden State will add 11.3 million new residents, and the ensuing land development will undoubtedly encroach on fragile habitat. Because the growth is almost entirely due to immigration, the newcomers and their offspring tend to be blamed for the state’s ecological woes. But even if California closed its borders to all future immigration, it wouldn’t solve any of the most vexing environmental problems, particularly the shrinking water supply. Consider that up to three-quarters of the state’s urban water use goes to landscaping–an activity more frequently associated with the wealthy and middle class than the newly arrived.

Most land-use experts concur that population growth isn’t the primary cause of environmental degradation. Rather, historic land-use patterns, which have resulted in a car-dependent culture, continue to wreak havoc on the natural world. And while it undercuts their own best interests, Californians hate density (a term often erroneously confused with crowding). Paris is one of the most densely populated cities in the world, yet it is heralded as one of the most livable. Unfortunately, most Californians think “livable” equals a single-family home with a yard, even if it entails a three-hour daily commute and horrible air quality. That’s why the state has become synonymous with sprawl. And according to the National Wildlife Federation, sprawl is the leading cause of species imperilment in California, outranking all other factors. While countless plants, insects, reptiles, birds and animals indigenous to California survived the Ice Age, they may be defenseless against the Age of the Subdivision.

A 2001 Sierra Club report that examined nationwide land-use patterns reached similar conclusions. The report found that population growth accounts for only 31 percent of America’s land consumption. Much of the rest can be blamed on ill-conceived land-use planning and government subsidies that encourage sprawl. According to Cornell University professor Rolf Pendall, “It is clear that population increases are not the only contributor to sprawl. Increasing population growth is most problematic when it happens in regions with poor land-use decision-making.”

The problem with McKee’s numbers-trump-behavior argument is that it unintentionally absolves societies–like the United States–that largely keep their population growth in check. However, when the United States withdrew from the Kyoto Protocol negotiations in 2001, it committed to a path of habitat destruction that outweighs any progress it can make in reducing its population.

Nevertheless, population growth does pose a grave risk to our global environment. As we add enough new people to the planet every thirty-eight days to populate a new New York City, McKee’s call to stem and perhaps even reduce our numbers is undoubtedly warranted. The Bush Administration’s withdrawal last July of the $34 million it had promised to support the UN Population Fund wasted an opportunity to spread the message of responsible family planning. While the move understandably drew criticism from women’s rights advocates, few discussed the decision’s environmental fallout. As McKee dejectedly notes, “It comes down to this question: do we want fewer children who have more to appreciate, or more children who have less to appreciate?” And don’t count on a mighty plague to restore the Earth’s equilibrium. McKee maintains that “the rise of disease probably will not be enough to seriously stem our persistent population growth–it will just be enough to make us miserable.”

Unfortunately, McKee, much like mankind, waits until the final chapter to discuss possible solutions. And even then, his suggestions are vague. Sparing Nature calls for population-growth abatement and improved family planning. But the only proposal he offers is to foster a global conscientiousness through education about the perils of overpopulation. It’s a noble-sounding gesture, but is it realistic? McKee briefly cites one successful model: The Iranian government offered free vasectomies for married men, distributed contraceptives and slashed its population growth in half. It’s a program that should definitely be studied and perhaps replicated.

While McKee believes that eco-friendly lifestyle choices are well-meaning, he thinks it would be more beneficial, and perhaps easier, simply to cease population growth worldwide. But in the absence of viable population-reduction prescriptions, conservation efforts remain our greatest chance for reversing global cataclysm.

While Sparing Nature considers the “think globally” facet of environmentalism, Lis Harris’s Tilting at Mills scrutinizes the “act locally” component. Expanded from a New Yorker article, this dourly quixotic tale recounts one man’s failed endeavor to enact a micro solution to a macro problem.

Driven by the knowledge that less than 20 percent of the world’s virgin forests remained intact and that much of that was under siege, Natural Resources Defense Council scientist Allen Hershkowitz wanted to advance international habitat conservation through a visionary South Bronx project. Hershkowitz devised a way to create an eco-friendly paper-recycling mill on a seventeen-acre parcel of the Harlem River railyard that would limit the demand for virgin paper products, preserve some of the world’s great ecosystems (5.1 million trees each year, to be exact) and reduce the amount of waste paper heading for landfills and incinerators, while cleaning up an urban brownfield and providing up to 600 full-time jobs for an impoverished community.

The Bronx Community Paper Company was owned by a once successful and admired community organization, the Banana Kelly Community Improvement Association. But in reality, BCPC was Hershkowitz’s baby, and his employer, the powerful NRDC, served as godparent. And if ever there was a good place to bring to life such a venture, it was New York City–dubbed the Saudi Arabia of wastepaper for its bountiful postconsumer supply. The five boroughs consume 1.5 million tons of newsprint a year. By comparison, all of Canada consumes 1.2 million tons annually. The city also discards about 3.6 million tons of paper every year, with at least 80 percent of it going straight to the landfill or incinerator.

What ensued was a sordid tale of pride and corruption. The book details how the BCPC project was unable to transcend a number of obstacles, including political turf wars; Banana Kelly’s mismanagement of millions of dollars in funds; misguided opposition from the community; and perhaps even the well-meaning Hershkowitz, who seemed unwilling to compromise on any part of his overarching goals.

By offering the dream-crushing account of the otherwise typical tale of an expensive municipal deal gone sour, Harris illustrates the complexity of driving an environmentally progressive project through the labyrinthine halls of local governments and community basements. While Hershkowitz jumped at the chance to show how industry had the potential to promote humanistic goals, few, including his fellow enviros, shared his unyielding enthusiasm. Hershkowitz saw the mill as a chance to bring together “cultures (business, community, environmental) that rarely spoke each other’s language, to actually change the way people think about industrial development.”

Initially, the proposed project garnered a great deal of support from powerful allies, like Governor George Pataki and eventually the Clinton Administration. But Harris reports that the South Bronx Clean Air Coalition became a vocal and pivotal critic after it tried unsuccessfully to extort money from the BCPC in exchange for its support. The coalition subsequently waged a public relations war fraught with misinformation, including charges that the mill would poison babies.

The smear campaign found a receptive audience with local environmental justice advocates, including one NRDC envoy, who had grown wary of what was seen as a movement oblivious to the toxic dumps that were continually sited in poor communities. Harris writes, “There was a certain suspicion in the environmental justice world that the Timberland and Patagonia crowd, the trail hikers and tree huggers, simply didn’t have that much interest in the environmental problems of poor people, especially poor urban people.” Had it succeeded, however, the Bronx mill would have reduced the need for polluting landfills and incinerators, which are predominantly built in black and Latino neighborhoods.

Amazingly enough, according to Harris’s history of the eight-year debacle, the NRDC dealt the proposed mill a devastating setback by unceremoniously dumping the venture after being hit with a potentially debilitating lawsuit by one of the subcontractors. But Tilting at Mills suggests that the nonprofit had already grown disenchanted by this point with how enmeshed Hershkowitz had become with the project. Harris writes that for the NRDC, “there was strong resistance to crossing over the line between business and advocacy–to going beyond the role of advisers–a step that Hershkowitz so passionately believed had to be taken, lest the movement become irrelevant.”

Ultimately, the paper industry dealt the mill its fatal blow. Though several major paper companies feigned interest throughout the process, Harris reports that they didn’t want the mill to come to fruition, because no one wanted to facilitate supply entering the marketplace and driving down newsprint prices.

Tilting at Mills illuminates the unavoidable tragedy that the mill’s collapse spells for the people who live downwind from a future incinerator or the species lost when a forest is clearcut. Unfortunately, Harris reveals, that’s just business as usual.