When Extinction Is Warranted: Invasive Species, Suppression-Drives and the Worst-Case Scenario

ABSTRACT

Most current techniques to deal with invasive species are ineffective or have highly damaging side effects. To this end suppression-drives based on clustered regularly inter-spaced short palindromic repeats (CRISPR/Cas9) have been touted as a potential silver bullet for the problem, allowing for a highly focused, humane and cost-effective means of removing a target species from an environment. Suppression-drives come with serious risks, however, such that the precautionary principle seems to warrant us not deploying this technology. The focus of this paper is on one such risk – the danger of a suppression-drive escaping containment and wiping out the target species globally. Here, I argue that in most cases this risk is significant enough to warrant not using a gene-drive. In some cases, however, we can bypass the precautionary principle by using an approach that hinges on what I term the ‘Worst-Case Clause’. This clause, in turn, provides us with a litmus test that can be fruitfully used to determine what species are viable targets for suppression-drives in the wild. Using this metric in concert with other considerations, I suggest that only three species are currently possible viable targets – the European rabbit, ship rat and Caribbean Tree Frog.

KEYWORDS:

• Bioethics
• gene-editing
• CRISPR/Cas9
• invasive species
• conservation
• precautionary principle

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

1. For a good discussion of playing god see Evans (2002). Intrinsic value we will return to later, but Rolston (1999) is the only positive argument I can find in favor of this position. For technological reliance, both White (1967) and Scott (2011) provide nice overviews of how technological advances interact with environmental concerns. For pragmatic concerns, work by Roberts et al. (2017), Moran and Jarvik (2010), H. Zhang et al. (2014), and (2015)) talk about why problems like off-target effects, and horizontal gene transfer are, even today, relatively minimal concerns for the technology.

2. It is worth noting here that in some cases the global elimination of the species is actually the goal of the project. One approach that has been floated for dealing with the malaria crisis has been to wipe out malaria-carrying mosquito species using a suppression-drive, in which case scientists are obviously not trying to mitigate the chance of escape (A. A. Hammond et al., 2016)

3. It’s been suggested that European rabbits are the first recorded invasive species, with Pliny the Elder noting in the Naturalis Historia (VIII.80) that they were invasive to the Balearic Islands around 75AD where they caused famines, brought down trees, and collapsed houses, leading to Divine Augustus sending a troop of soldiers armed with ferrets to help the region.