TWN Info Service on Biosafety
11 December 2025
Third World Network
www.twn.my
Dear Friends and Colleagues
Gene drives, species complexes and the risks of collateral damage
A new article published in the prestigious PNAS journal raises serious concerns about gene drive technologies affecting non-target species. It further critiques the risk assessment frameworks proposed by developers attempting to circumvent the problem, which could create a “risky trend in vector control”.
Gene drive technologies, a type of genetic engineering designed to spread traits through entire populations, are being targeted at species that belong to ‘species complexes’, i.e. a group of similar species that are able to inter-breed. Lead gene drive projects (as well as other novel technologies e.g. CRISPR-based ‘precision guided’ sterile insect technique), are targeting the Anopheles gambiae mosquito species complex. This opens the door for unintended effects such as unintended gene flow, including to species that do not transmit malaria.
Developers, acknowledging that gene drive constructs may not be confined to a single species, have attempted to re-frame the risk by expanding the definition of a target species to include the entire complex. As the paper warns, this “risks reframing collateral impacts as intentional outcomes, narrowing, rather than broadening, the scope of ecological and regulatory considerations”. Indeed, species within a complex are ecologically diverse, and may play different and critical roles in ecosystems. As such, “The assumption that modifying an entire species complex will yield only beneficial outcome is scientifically misleading, overly reductive, and ecologically risky”.
Hybridisation also opens the door to evolutionary uncertainty. As the author elaborates, “Hybrid species created as a result of gene drives could have unpredictable ecological traits that make them more invasive, harder to control, or lead to negative epidemiological consequences. This is not just theoretical, but highlighted by the hybridization between Culex pipiens and Culex quinquefasciatus mosquitoes on Madera. This hybridization may have promoted a more opportunistic feeding behavior, thus contributing to the human transmission of zoonotic arboviruses such as West Nile Virus”.
Crucially, the paper makes clear that any risk assessment that focuses on one single species within a complex would fall short of capturing the range of potential impacts of gene drive releases. “Researchers must therefore make sure to incorporate risk assessments that take into account the effects on numerous species and make a concerted effort to understand the downstream effects.”
With best wishes,
Third World Network