Humanity's main impact on the extinction rate is landscape modification, an impact greatly increased by the burgeoning human population. Now standing at 5.7 billion and growing at a rate of 1.6 percent per year, the population of the world will double in 43 years if growth continues at this pace. By draining wetlands, plowing prairies, logging forests, paving, and building, we are altering the landscape on an unprecedented scale. Some organisms do well under the conditions we've created: They tend to cope well with change, tolerate a broad range of habitats, disperse widely, and reproduce rapidly, and they can quickly crowd out more specialized local species. City pigeons, zebra mussels, rats, and kudzu and tamarisk trees -- these are examples of what biologists call "weedy" species, both animals and plants. Many weedy species will probably survive, and even thrive, in the face of the current mass extinction. But thousands of others, many never known to science, are likely to perish.
And what is the fate of our own species likely to be, if we really are in the midst of a sixth mass extinction? One possibility is that as diversity and abundance wither, the species causing it all -- Homo sapiens, the most dominant species in history -- could also be on the road to oblivion. But another possibility is that Homo sapiens, which has proved to be a very effective weedy species itself, will persist. That's the view of paleobiologist David Jablonski, who sees us as one of the survivors, "sort of picking through the rubble" of a world that has lost much of its biodiversity -- and much of its comfort. For along with that species richness, the ecosystem is likely to loose much of its ability to provide many of the valuable services that we take for granted, from cleaning and recirculating air and water, to pollinating crops and providing a source for new pharmaceuticals. And while the fossil record tells us that biodiversity has always recovered, it also tells us that the recovery will be unbearably slow in human terms -- 5 to 10 million years after the mass extinctions of the past. That's more than 200,000 generations of humankind before levels of biodiversity comparable to those we inherited might be restored.