Until the 13th century, the only land mammals in New Zealand were bats. In this furless world, local birds evolved a docile temperament. Many of them, like the iconic kiwi and the giant kakapo parrot, lost their powers of flight. Gentle and grounded, they were easy prey for the rats, dogs, cats, stoats, weasels, and possums that were later introduced by humans. Between them, these predators devour more than 26 million chicks and eggs every year. They have already driven a quarter of the nation’s unique birds to extinction. [...]
In recent years, many of the country’s conservationists and residents have rallied behind Predator-Free 2050, an extraordinarily ambitious plan to save the country’s birds by eradicating its invasive predators. Native birds of prey will be unharmed, but Predator-Free 2050’s research strategy, which is released today, spells doom for rats, possums, and stoats (a large weasel). They are to die, every last one of them. No country, anywhere in the world, has managed such a task in an area that big. The largest island ever cleared of rats, Australia’s Macquarie Island, is just 50 square miles in size. New Zealand is 2,000 times bigger. But, the country has committed to fulfilling its ecological moonshot within three decades. [...]
Other skeptics say that the task is simply too huge. So far, conservationists have successfully eradicated mammals from 100 small islands, but these represent just 10 percent of the offshore area, and just 0.2 percent of the far larger mainland. It’s one thing to cull pests on small, waterlocked pimples of land whose forests are almost entirely owned by the government. It’s quite another to repeat the feat in continuous stretches of land, dotted by cities and private homes. [...]
Through mathematical simulations conducted with colleagues at Harvard, he has now shown that gene drives are even more invasive than he expected. Even the weakest CRISPR-based gene drives would thoroughly invade wild populations, if just a few carriers were released. They’re so powerful that Esvelt says they shouldn’t be tested on a small scale. If conservationists tried to eliminate rats on a remote island using gene drives, it would only take a few strongly swimming rodents to spread the drive to the mainland—and beyond. “You cannot simply sequester them and wall them off from the wider world,” Esvelt says. They’ll eventually spread throughout the full range of the species they target. And if that species is the brown rat, you’re talking about the entire planet.
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