Extinction on demand
Gene drive technology could rid the world of rats forever. But is that really what we want, asks Charlie Mitchell.
It’s one thing to play God within one’s own environment. But what happens if your experiment spreads across borders, into places that can’t object? What if New Zealand, with good intentions, causes an international ecological incident?
It’s a question authorities need to seriously consider in their pursuit to cleanse this country of predators, a new study argues. And it needs to be sorted out quickly.
A study released today by the Sustainability Council, with funding from the Law Foundation, examines the potential impact of gene drives and New Zealand’s role in globally governing the technology as the push towards Predator-Free 2050 accelerates.
A gene drive is an emerging technology with intimidating implications. By altering the genome of a handful of individuals and releasing them into the wild, you could circulate a particular gene among the entire population.
In rats, for example, you could edit a gene that ensures it only produces male offspring and spread it through the population with a gene drive. After around a decade of breeding daughterless rats, you would eventually have none left; a bloodless end to a species.
The major issue is that, once a gene drive was let loose, it could be difficult to control. It would spread through the population like genetic wildfire, with no respect for geographic or political boundaries. While it could theoretically be reversed by releasing another gene drive cancelling out the original, it could spiral out of control once it has spread widely.
If that was to happen, there could be serious political implications. What if, a couple of decades from now, we release rats, which have been genetically edited to produce only male offspring, in a certain part of the country.
A farmer in the United States – where rats cause many billions of dollars of damage to crops each year – decides to smuggle a gene-edited rat from New Zealand to kill the rats damaging her crops.
Modelling has shown just one geneedited rat has a small chance of spreading the gene widely in a new population. A dozen gene-edited rats would make it virtually guaranteed.
If that happened, the gene drive could spread wider and wider, until much of the United States had lost its rats. Then it spreads into Canada and Mexico, then further into South America. At that point, you would assume it would get everywhere.
While we may hate rats, in some countries they are a dietary staple, and in others they pollinate plants and spread seeds. Like all species, they are native to somewhere – in this case, much of Eurasia.
So what would happen if New Zealand triggered this cascade? No-one knows.
‘‘If New Zealand is serious about exploring the use of gene drive to help protect native species, it should be leading development of the international rules required, as that will not be easy,’’ say the study’s coauthors, Sustainability Council executive director Simon Terry and projects director Stephanie Howard.
There is ‘‘real urgency’’ for a global agreement to govern gene drives, they say. While it remains theoretical, research is gathering pace, and the technology is likely to become viable within a few years.
‘‘A country that is otherwise vigilant to biosecurity risks should be alive to the ways in which gene drive releases in other countries could provide a significant biosecurity threat,’’ they say.
‘‘This is why New Zealand should back strong international rules.’’
THE SCIENCE
Even science-fiction authors didn’t imagine a world in which we could genetically engineer entire species, taming the law of evolution that has ruled the Earth since life began.
The most likely way a gene drive would work is through a technique called CRISPR, which was developed in 2012.
CRISPR, put simply, allows scientists to find and replace any section of DNA.
They do this by programming a piece of code matching the section they want to replace and attaching it to a protein, which finds the matching section in the DNA sequence. The protein cuts that DNA sequence and the programmed section replaces it.
When the technology becomes more advanced, CRISPR could be used for socalled ‘‘designer babies’’, altering the genes that produce traits around intelligence or physical features. Some think it could be used to recreate extinct species.
But for now, it’s more likely to be used to create crops that are more nutritious, or resistant to climate change, or to cure diseases that result from defective genes.
Shortly after the CRISPR technique was discovered, another potential use was found, one with enormous consequences. Gene drives had been mooted in the 1990s, but were not technically feasible, until CRISPR.
When two individuals breed, each one contributes 50 per cent of the offspring’s genes. If you were to edit a rat’s genome with CRISPR so it could produce only male offspring, there would be a 50/50 chance its offspring would have that gene. Over the generations, a smaller and smaller number of rats would have it, until it was diluted out.
But a gene drive can overcome this natural law of inheritance and turn a 50 per cent chance into a guarantee.
A gene placed into a genome with CRISPR can be programmed to selfpropagate. It would effectively copy and paste itself over the partner’s gene, meaning the offspring would be able to inherit only the edited gene.
Every rat born from the gene-edited original would be male, as would every rat born in subsequent generations.
The process is slow because it moves only vertically, down generations. But for species that reproduce quickly, like rats, you could likely eradicate them within a decade, without killing a single one.
‘EXTINCTION ON DEMAND’
The polite term for this is ‘‘sculpting evolution’’, but it has also been described, more ominously, as ‘‘extinction on demand’’.
If New Zealand is serious about exploring the use of gene drive to help protect native species, it should be leading development of the international rules required, as that will not be easy. Simon Terry, Sustainability Council executive director and Stephanie Howard, projects director