A Culex quinquefasciatus mosquito is seen on the skin of a human host in this 2014 picture from the Center for Disease Control. (Reuters/CDC/James Gathany)

Scientists from around the world are currently gathered in Hawaii for an international conservation congress, where they’ve spent the past week discussing the most pressing issues facing the environment today. One topic on the table is a form of genetic editing called “gene drive” technology, which can be used to alter — or even wipe out — entire species. And while some experts have argued that the practice could be a useful conservation tool, others have warned that its impact on the environment could be devastating should it get out of control.

Members of the International Union for Conservation of Nature (IUCN), which is holding its World Conservation Congress in Honolulu through Sept. 10, recently approved a motion that would prohibit the organization from supporting or endorsing any research or field trials on the use of gene drives until a comprehensive assessment of the technology’s effects has been undertaken.

The motion is nonbinding and does not dictate the regulations that individual countries may choose to establish for themselves. But it does reflect a growing concern among both scientists and environmentalists about the technology’s potential power to irrevocably alter species and reshape ecosystems.

A “gene drive” is a stretch of DNA that gets passed on to offspring more frequently than regular genes. In most sexually reproducing organisms, offspring have a 50 percent chance of inheriting a given trait from either one of their parents. Gene drives increase the odds.  

To be clear, gene drives are a naturally occurring phenomenon — they’re found in all kinds of species in nature. But it wasn’t until recently, with the advent of new genetic engineering tools, that scientists realized they could be harnessed by humans.

Genetic editing tools such as CRISPR allow scientists to make precise cuts and splices in an organism’s DNA, allowing them to physically alter genes and change the traits that they code for. Recently, researchers also realized that such tools could also be used to attach gene drives to DNA sequences, greatly increasing the likelihood that these genes would be passed on.

Scientists have already begun to brainstorm ways this technology could be used for conservation purposes. In Hawaii, for instance, some scientists have suggested it could be used to save a group of endangered endemic birds known as honeycreepers. One of the many threats facing these birds is avian malaria. Scientists have suggested that gene drive technology could be used to render mosquitoes on the islands incapable of transmitting the disease, by tricking the mosquitoes’ immune systems into attacking the parasite that causes malaria.

It’s a different concept from the genetically modified mosquitoes developed by biotech company Oxitec, currently being used to combat Zika in Brazil. The Oxitec mosquitoes are engineered with a “self-destruct” gene that causes their offspring to die before reaching adulthood. While these mosquitoes have been genetically modified, there is no gene drive involved.

However, gene drive technology could theoretically be used to kill off species in a similar way. Some scientists have suggested, for instance, that gene drives could be used to eradicate invasive populations of rats and mice from islands, where they’ve been known to damage local ecosystems, by engineering the rodents to only produce male offspring. And the same principle could theoretically be used to knock out mosquitoes as well.

But while there’s clear potential for the technology to do good, many experts have expressed concern about the potential changes it could cause in the natural world. Gene drives in their most aggressive forms have the potential to spread irreversibly throughout entire species, and it’s not yet clear how this effect could impact the environment.  

In an open letter aimed at members of the IUCN, worried environmentalists expressed their concern about the technology’s implications. “Given the obvious dangers of irretrievably releasing genocidal genes into the natural world, and the moral implications of taking such action, we call for a halt to all proposals for the use of gene drive technologies, but especially in conservation,” they wrote.

However, it’s important to note that gene drive technology can take several different forms, and some are safer than others, said Floyd Reed, an associate professor of biology at the University of Hawaii. Reed’s lab is currently involved in gene drive research on fruit flies, with plans to begin moving forward with mosquitoes next.

Reed’s research involves a genetic phenomenon known as “underdominance,” which can be used to implement a type of drive system that potentially can be halted before it gets out of control. In this system, a trait’s ability to spread is dependent on what percentage of the population has it to begin with.

Typically, in this system, there’s a frequency threshold that a trait must cross before it begins to be favored. In order to introduce a desired trait into a population, researchers would theoretically have to release enough individuals expressing that trait to be sure it would spread. Then, if they ever wanted to phase it out, they could add enough of the “regular” type of individuals back into the population to reverse the effect.  

“I think that the most important point is for people to understand the different types of technologies when they say ‘gene drive,’ ” Reed said. Although reversible systems are still not completely understood, a moratorium on research or even field trials for this type of technology may not be warranted, he said, so long as they’re subject to rigorous regulation and public consultation.

Irreversible, or “global” gene drives, on the other hand, should require much greater caution, Reed noted, since they may become impossible to stop once they’re put in motion. As a result, holding off on trials may be wise until a better understanding of the technology’s potential ecological effects can be achieved.

Kevin Esvelt, leader of the MIT Media Lab’s Sculpting Evolution group and a pioneer of gene drive technology, is among the most cautious voices in the scientific community. When it comes to building global gene drive systems in the lab — the type that could spread throughout the world — such research “should not be undertaken lightly,” he said in a written response to the IUCN motion, emailed to The Washington Post.

Esvelt participated in a panel discussion at the World Conservation Congress just last week focusing on the use of gene drive technology for conservation purposes in Hawaii. While the development of a global gene drive system for use on the islands has not yet been proposed by any researchers, Esvelt noted that he would oppose the effort if it were.

“Unless the goal is an overriding ethical imperative — such as combating one of the worst diseases to afflict the world — we don’t know enough to try,” he wrote. “At this point, no one should be building a global drive that might spread in the wild unless they are attempting to prevent a disease that infects thousands of people and kills hundreds of people every day. Those are the only problems serious enough at this early stage.”  

For the time being, a major priority should be better systems of governance for the technology, Reed said. For its part, the National Academies of Sciences, Engineering and Medicine conducted a year-long study on gene drives, released earlier this summer, and concluded that while the technology carries risks, its benefits hold enough promise to warrant continued research. But when it comes to actual regulation of the research, the country may still be lacking.  

“I think we do not have the proper guidance and regulation, and we need it — we need to have that dialogue,” he said.  

Esvelt added that transparency is key with this type of technology. While convention often favors science conducted behind closed doors, scientists working on gene drives should make their proposals public well before they begin a project, he said — and any proposal that seeks to alter the environment should be guided by consultations with local communities.  

“IUCN doesn’t need to support or endorse gene-drive technologies at this time,” he wrote. “It’s too early. But conservationists should certainly join discussions of whether, when, and how we should alter the shared environment. Why? Because we are finally learning to speak the language of nature. With sufficient cooperation and humility, we might even use it wisely.”

The Post's Brady Dennis talks with Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, about the process of getting a potential Zika vaccine tested and ready for the public. (Video: The Washington Post/Photo: Sammy Dallal for The Washington Post)