It’s an uncomfortable thought: Human activity causing the extinction of thousands of species, and the only way to slow or prevent that phenomenon is to have smaller families and forego some of the conveniences of modern life, from eating beef to driving cars, according to Stanford University scientists Paul Ehrlich and Robert Pringle.

This extinction—the sixth in the 4-billion-year history of the Earth—"could be much more catastrophic than previous ones," says Ehrlich, author of the controversial Population Bomb, which predicted that hundreds of millions of people would starve to death in the 1970s. That fate was forestalled by the green revolution in Asian agriculture, in which new strains of cereal crops plus enhanced use of fertilizer and irrigation allowed farmers to grow enough food to feed a burgeoning population. But this is a new threat: "Anything in the vicinity of the previous ones," Ehrlich says, such as the mass extinction at the end of the Cretaceous that killed half of all species, including the dinosaurs, "would wreck civilization."

Right now, at least 2,000 frogs, salamanders and other amphibians are in danger of going extinct, according to a survey by biologists David Wake and Vance Vredenburg, writing in the Proceedings of the National Academy of Sciences USA. Coastal seas and estuaries have lost as much as 91 percent of certain species, such as oysters, according to another survey. And nearly 50 percent of all temperate grasslands and forests have disappeared.

But through it all the species responsible for this change—through overuse, pollution and other impacts—has continued to thrive and multiply, reaching roughly 6.7 billion in population and counting.

"The fate of biological diversity for the next 10 million years will almost certainly be determined during the next 50 to 100 years by the activities of a single species," write Ehrlich and Pringle in their proposal for addressing the biodiversity crisis. Adds Pringle: "The world's remaining wild areas and the species in them are being pulverized, and that's a multi-layered tragedy."

That’s why Ehrlich and Pringle call for educating women, which has slowed or stopped population growth in the developed countries of Europe. "Education and employment—for women especially—along with access to contraception and safe abortions are the most important components," they write. Adds Ehrlich: "The most basic response is to get going on stopping population growth and starting a decline. Second is doing something about consumption. If you don't do anything about those, then you are in trouble in all the others: more people, means more greenhouse gases, which means more rapid climate change."

A series of studies in PNAS detail the extent of the sixth extinction. As of the end of last year, more than 16,000 species faced extinction and 785 had already been lost, according to the International Union for the Conservation of Nature. But biologist E. O. Wilson notes that most species remain to be discovered and may be winking out without humans noting their passing; he estimates that at least 12,000 species are dying out every year.

Amphibians are among the most threatened thanks to a lethal combination of climate change, habitat destruction and a deadly fungal infection (chytridiomycosis)—and many unique species, including frogs that reared their young in their own stomachs from Australia, have already disappeared. In fact, last year's prediction by the U.N. Intergovernmental Panel on Climate Change that amphibians who lived on mountainsides would increasingly go extinct is now reality.

Meanwhile, human use of sea life, particularly overfishing, has emptied the oceans. Longline fishing records reveal that nearly 90 percent of pollock and haddock have disappeared in the last century and cod alone has decreased by 96 percent since 1852. Large sharks continue to dwindle while other species, such as clam-eating cownose rays, have exploded in the absence of predators. Jellyfish are among the only living things to thrive in the oxygen-starved waters of expanding dead zones. Even the Great Barrier Reef has living coral on only 23 percent of its surface, one-half of levels in 1980.

With the human population growing—predicted to reach 9.3 billion by 2050—along with the need for more food, more goods and more resources, the outlook for other species seems grim. But the outlook is also troubling for humans, note Ehrlich and Pringle. In particular, humanity relies on the services provided by the natural world for free, such as clean water. Then there are the bees: Regardless of whether honeybees become extinct as a species as a result of colony collapse disorder, climate change and other threats, the local extinction of various honeybee populations and the pollination they provide could spell disaster for human agriculture.

As a result, Ehrlich and Pringle also call for endowments to perpetually fund conservation areas, such as the Paz Con la Naturaleza initiative under consideration in Costa Rica that would generate $500 million in one-time money from taxpayers and be used to fund conservation in perpetuity for the national park system.

They also call for making agricultural land more hospitable to wildlife, recognizing the economic value of various ecosystem services like pollination and returning degraded lands to a natural state to help stave off this biodiversity crisis, with its attendant effects on humanity. "There are desperately poor people surrounding many of these reserves," Ehrlich notes. "If I was there, I would shoot the hippo and eat it too."