By Jemima Frame
Genetics is an ever-growing field in biology, with new techniques and technologies still being discovered. With these new discoveries come new potential uses, one of these being evolutionary warfare. For the past 20 or so years there has been research into how to alter certain species genomes in order to reduce their numbers, or potentially eradicate them. Research has mainly been focused on invertebrates, such as mosquitoes, however now research efforts are being directed to certain vertebrates including possums. The ability to eradicate species which cause harm to humans could be seen as a beneficial solution, however once we start to use this new technique on the wild populations there is no turning back, and there is no telling how it may affect the broader evolutionary picture. We are potentially producing one of the next big threats to the global ecosystem.
One of the first experiments to reduce species numbers was on screwworms, parasites which feed on living flesh, including humans but more often cattle. In the 1950’s screwworms were debilitating the beef industry in the US by feeding on all their livestock, so a scientist, Edward Knipling, tried to solve this problem. He came up with a revolutionary idea to sterilise the population. He, along with his team, sterilised thousands of male screwworms through radiation directed at their reproductive organs (WYSS, 2000). The theory was if these sterile males were released into local populations, most fertile females would mate with sterile males. This would therefore reduce the number of offspring each generation, and the screwworm population would begin to decline before eventually going locally extinct. This sterile-insect approach proved to be very successful and by 1966 screwworms had been completely eradicated in the US and by 1991 Mexico and several other countries in Central America had removed all screwworm populations (Scott et al., 2017). The success of this technique opened up possibilities for a new type of warfare; evolutionary warfare, in which humans could wipe out an entire species by editing their genome.
While editing screwworms genome through radiation was a success it was only inducing random mutations, scientists couldn’t control what mutations occurred therefore the organisms could end up with much worse mutations than being sterile. This made this approach risky for other species as they didn’t know how they would react to the radiation, therefore when technology progressed and CRISPR was discovered, the editing of genomes became much more precise and accurate. Mosquitoes became the target for this new experiment, insects responsible for millions of human deaths due to being carriers of malaria, yellow fever, dengue fever and others. The theory was that they could influence the sex ratio of mosquitoes to bias it towards males, as only female mosquitoes are carriers of malaria. They did this through a concept called ‘gene drive’ (Pugh, 2016). Gene drives are selfish DNA sequences which are inherited much more often than they would by chance, allowing desirable characteristics within these selfish genes to be spread throughout the whole population at a much faster rate. CRISPR allows us to insert target sequences into these selfish genes, essentially building artificial gene drives. There are currently two artificial gene drives in development which are focused on altering mosquitoes’ genomes (Pilcher, 2020). One of them comprises of an edited gene which biases the sex ratio, resulting in all male offspring. The other involves an altered doublesex gene which is responsible for female development. When females inherit two copies of this gene they will now be sterile, one copy of the gene will not affect them, allowing some females to reproduce and pass on the edited genes to the next generation. This will result in a decrease in offspring every generation, and therefore a decreasing population (Pugh, 2016). When this gene drive was tested in a contained population of 450:150 normal:edited mosquitoes it was very successful with the complete population’s crashing between 7-11 generations (Pilcher, 2020).
This discovery provides a potential solution to malaria, which kills hundreds of thousands of people every year, however there is a danger to releasing these edited genes into the wild. Once the genes are released, we can no longer control how they are passed on, and there is a good chance that they could spread throughout the entire population, rendering a whole species extinct. While the loss of a mosquito’s species would have little ecological significance and would save thousands of lives, taking this step brings us into a new era where we become able to wipe out entire species to benefit ourselves. It also allows us to start to use these methods on other species which may have more ecological significance. For example, New Zealand aims to eliminate all invasive vertebrate predators by 2050, a plan called Predator Free 2050 (Murphy et al., 2019). New methods are needed for New Zealand to reach this goal and there has been suggestions that gene drives can be used to create, for example, ‘suicide possums’ which will be sterile and therefore reduce the population until they are eventually wiped out (Pilcher, 2020). While possums can be detrimental to local species in New Zealand, the creation of ‘suicide possums’ to create local extinction of the species in New Zealand could potentially be passed onto possums in Australia, where possums are protected.
This shows the unpredictability of gene drives and other methods of evolutionary warfare, and shows that we are unable to control it, therefore the solutions that it provides can very quickly be overshadowed by the damage they may cause. More research should be done into the possible effects of species extinction as well as tighter restrictions on which species to use it for before evolutionary warfare becomes a viable option.
WYSS, J. H. (2000) Screwworm Eradication in the Americas. Annals of the New York Academy of Sciences; Ann N Y Acad Sci. 916 (1), 186-193. Available from: doi: 10.1111/j.1749-6632.2000.tb05289.x.
Scott, M. J., Concha, C., Welch, J. B., Phillips, P. L. & Skoda, S. R. (2017) Review of research advances in the screwworm eradication program over the past 25 years. Entomologia Experimentalis Et Applicata. 164 (3), 226-236. Available from: doi: 10.1111/eea.12607.
Pugh, J. (2016) Driven to extinction? The ethics of eradicating mosquitoes with gene-drive technologies. Journal of Medical Ethics; J Med Ethics. 42 (9), 578-581. Available from: doi: 10.1136/medethics-2016-103462.
Pilcher, H. (2020) Life Changing; How Humans are Altering Life on Earth. London, Bloomsbury Sigma.
Murphy, E. C., Russell, J. C., Broome, K. G., Ryan, G. J. & Dowding, J. E. (2019) Conserving New Zealand’s native fauna: a review of tools being developed for the Predator Free 2050 programme. Journal of Ornithology. 160 (3), 883-892. Available from: doi: 10.1007/s10336-019-01643-0.