Genetic Engineering has been in the popular lexicon since the concept was first introduced in the science fiction book “Dragon’s Island” in 1951. Since the discovery of the double helix in 1953, our understanding of genetics has increased massively. Unfortunately, however, there is still no sign of genetically engineered superheros or Captain Americas.
CRISPR technology (Clustered Regularly Interspaced Short Palindromic Repeats) is a new and extremely powerful genetic tool. It probably won’t give us a super soldier, but it is a major step in applying our knowledge of genetics to the real world. Simply put, CRISPR allows us to edit genes by cutting out those which may be deleterious (bad), and replacing them with genes that could be considered advantageous. CRISPR is not a novel technology to the bacteria which evolved it – but the advent of CRISPR use in laboratory settings has excited the science community. One of the numerous theoretical applications associated with CRISPR technology is what is known as the ‘gene drive’.
Genetic approaches to controlling populations have been around for a while. The issue was how to pass on these edited genes. After all, natural selection and evolution should see disadvantageous genes bred out. This is where the gene drive comes in. If we were to introduce an edited gene into a group of mosquitos and release them, the lab born mosquitos would breed with the wild population and pass on the edited gene. Inheritance would be minimal if the edited gene was designed to be deleterious because it would prevent the offspring from breeding successfully and passing the gene on any further.
If an edited gene is packaged together and inherited with CRISPR, however, then it cuts out the wild type gene in offspring, allowing it to be replaced with the edited gene. This process then continues over generations, ensuring that the edited gene passes on to a large percentage of the population. This is what is so revolutionary about the gene drive – it allows us to engineer natural selection.
“This is what is so revolutionary about the gene drive – it allows us to engineer natural selection.”
So, what could these edited genes do? Quite a lot, as it turns out. For example, there are three possibilities for reducing malaria. The first is to hinder the mosquitoes’ ability to pass on malaria (which is in fact caused by a protozoa parasite). The problem with this is that the malarial parasite could evolve to counteract this. The second option is to engineer the designed gene such that any carrier offspring is male – reducing the amount of females in the population capable of breeding. The third is to make all the mosquitos with two sets of the edited gene sterile, crashing their population. These are just a few ways in which a population could be severely reduced or destroyed through a gene drive system. It is not hard to understand why the idea of using gene drives for conservation, or even pest control, seems pretty tempting.
One of the first people to propose the gene drive as a means of population control was Kevin Esvelt from MIT. He suggested using the gene drive to control mosquito populations and, consequently, the spread of malaria. In the same paper he proposed another use of the technique – controlling invasive species. However, he has now teamed up with others to espouse the potential dangers of this approach. So, why the change of heart? Worldwide invasive species are estimated to cost $1.4 trillion. Invasive species don’t just live in equilibrium with native plants and animals – they outperform and outbreed them. Once invasive species are introduced it is almost impossible to get rid of them. Attempts thus far have usually involved consuming and expensive approaches – such as poison, traps or even shooting invasive goats out of helicopters, as is done in the Galapagos islands. Gene drives are a temptingly economic alternative management strategy. At the moment in New Zealand there is talk of using this method on rats, which are a serious invasive issue there.
“You would think that we learn, but we don’t – playing with ecosystems is a dangerous game.”
Biological controls for invasive species is not a new phenomenon. Cane toads were introduced into Australia in 1935 to control Greyback cane beetles. Unfortunately, no one had figured that the toads couldn’t reach the beetle to eat it. Cane toads have since then become an even larger pest in themselves Australia. They are so poisonous to native snakes, that the reptilian predators are evolving smaller skulls to avoid eating them. You would think that we learn, but we don’t – playing with ecosystems is a dangerous game. Since then there have been many such attempts at biological control – some have been successful, but most have been complete failures.
The issues with the gene drive is that it is analogous with creating a new invasive species. Say New Zealand decides to use a gene drive on possums which are invasive there. It’s not unreasonable to predict that a possum with the edited gene could find itself in Australia, where they are a protected species.
The gene drive has the potential to be an incredibly powerful. It allows us to alter the usual rules of natural selection. However, this power demands respect. We humans have had a disastrous history when it comes to our relationship with the environment, the impacts of which are increasingly obvious. Biological controls have been part of that history and if any good is to come from them, we must learn from our mistakes. If we are to use gene drives, individual cases must be agreed internationally. This is possible in the fight against malaria but with conservation it is important to remember all invasive species are an integral part of somewhere’s ecosystem. It should not be a case of discarding this promising avenue of research but to tread carefully, act proportionally and above all gene drive responsibly.
Peter Cox is the director of the podcast Trinity Talks Science, available from the 10th of December at http://duscisoc.ie/