What if scientists could wipe out an entire species of malaria-carrying mosquito across sub-Saharan Africa, and other tropical regions of the world, with a bit of genetic editing that would drive its swarms to extinction in just a few years?
Or, with the same tool, stop the spread of Lyme disease by eliminating the white-footed mice that serve as reservoirs for that parasite? Maybe rescue portions of the Galapagos by rubbing out invasive rats?
If this sounds like the stuff of futuristic fantasy fiction to you, you have missed the coverage gathering this summer around the promise and perils of “gene drive” technology, a simplified approach to genetic engineering with a clear capability to erase entire species within just a few generations. (The target insect’s or rodent’s generations, that is, not human ones.)
The topic is front and center this week at the World Conservation Congress in Hawaii, the quadrennial meeting of the International Union for the Conservation of Nature. Delegates there have voted overwhelmingly to call a temporary halt to development of gene drive techniques until the world has had to chance to reflect upon the many ways in which it could go way wrong.
That action follows publication of an open letter [PDF] signed by such luminaries as Jane Goodall, David Suzuki and Fritjof Capra declaring that gene drive technology, “which has not been tested for unintended consequences nor fully evaluated for its ethical and social impacts,” brings humanity to “a moral and ethical threshold that must not be crossed without great restraint.”
Most mainstream media coverage, however, has carried the sort of cheerful, gee-whiz tone of Saturday’s Wall Street Journal piece headlined, “Mosquitoes are deadly, so why not kill them all?”
There is no shortage of sound answers to that question, but before turning to them let’s talk a bit about the science that has made it necessary and really rather urgent. Since mosquitoes are the primary near-term targets of the technique, they offer a fine illustration.
Making mosquitoes all male
When a male and female mosquito mate, each of their offspring has a 50 percent chance of being female and a 50 percent chance of being male. This is more or less the same for all traits passed down genetically by all species, plant and animal, that reproduce sexually.
With the development of genetically modified crops, like pest-resistant corn, the goal was to insert new genetic traits within the organism. The gene drive method, in contrast, uses a simplified editing technique to make sure that only one version of a trait, like gender, can be passed along.
British scientists have demonstrated, at the petri-dish level, that it is possible to modify the chromosomes of a malaria-carrying Anopheles mosquito so virtually all of the offspring are male.
This carries a dual advantage for disease control: Only females can inject the malaria parasite with their bites. And an all-male population — already shown to be achievable in just a few generations of the fruit fly, that workhorse of testing for genetic inheritance — can no longer reproduce itself.
This is not the only high-tech approach under consideration right now for advanced mosquito/malaria control. It’s not to be confused, for example, with a work on getting insects to carry new genetic material that can resist or kill a virus like Zika. Or torpedoing population growth by introducing insects made sterile with radiation, or outfitted with bacteria that can be passed along to offspring with lethal effects.
Those tools have a lot of potential and have inspired their own controversy. But in potential impact they don’t approach the gene drive with its simple, quick capacity for engineered extinction.
Problem is — assuming that something might just possibly go wrong — it’s an extinction mechanism without a kill switch.
To its credit, the Journal story acknowledges (if only glancingly) that there are arguments for going slow with the gene drive approach to fighting Zika, malaria and other insect-borne diseases. So does an earlier piece (with a highly similar tone and headline) in Time magazine.
The case for precaution
They can be grouped in a few categories, and are discussed in more detail in this fine piece of a month ago in the journal Science:
- Mosquitoes play key roles in ecosystems, such as providing food for bats and other insectivores, and “scientists have minimal experience engineering biological systems for evolutionary robustness.”
- It’s possible that a gene drive might not distribute the intended trait throughout a target population, or might find its work blocked by a naturally occurring mutation, or might spread the trait to nontargeted species.
- It’s also possible that a gene drive could stimulate other unforeseen evolutionary responses over a longer term in both target and nontarget species.
- And, again, the ability to redress any of these unintended consequences could be sharply limited by the lack of reliable reversal mechanisms.
Even scientists championing gene-drive technique recognize and discuss these limitations and risks, but generally as little hurdles to be crossed somewhere down the road.
For example, the entomologist Zach Adelman of Texas A&M, who is trying to engineer a males-only rewrite to the chromosomes of the Zika-carrying Aedes aegypti mosquito, told the Journal that he sees the technology as “an all-powerful tool that will win the war for us, but that is exactly the sentiment that people felt when things like DDT first came along. … It’s good to be optimistic. But we need to be realistic as well. “
On the other hand, he says frankly that “I think it is our moral duty to eliminate this mosquito.”
And at the moment, that notion of a moral imperative in favor of rapid deployment rather than precautionary restraint seems to be dominating the conversation among many scientists — the views of Jane Goodall and the IUCN notwithstanding — and other powerful actors including Bill Gates, whose foundation has invested many millions in both the development of gene drive techniques and their eventual application.
Speaking to a Bloomberg reporter in June, Gates acknowledged that “there’s a still a fair amount of work to be done” and that “nothing is ready to be deployed today,” but these points were secondary to “my basic belief … that children dying of malaria is a bad thing, and that we should be able to meet these objections.”
Gates says he hopes to see gene editing used against HIV. His foundation has funded older gene-editing efforts against HIV, which were less efficient than [the new gene drive tool]. “HIV is still a lifelong disease, and any type of cure approach or some sort of way that you’d protect somebody on a lifelong basis, that would be invaluable, but that’s at a very early stage.”
And as a former Namibian health minister, Richard Kamwi, told Time:
A malaria vaccine has been 10 years down the road for 25 years. We need something now, before the tools we have stop working. I want to call on all the researchers and say that where they have been walking, they must start running. Where they have been jogging, they must start sprinting.