A bushel basket brims with sweet potatoes. (Margaret Thomas/The Washington Post)

One major reason the public is wary of genetically modified crops is the role humans play in shaping the plants’ traits. To make many genetically modified organisms (GMOs) for use as food crops, scientists insert genetic material into a crop’s DNA from a totally different species.

It certainly doesn’t sound “natural.” But this transfer of genetic material from one species to another isn’t as odd as you might think. In fact, it happens all the time in nature, as creatures ranging from fungi to bacteria have shown the ability to transfer bits of genetic material into other organisms’ DNA. Scientists have adapted this “horizontal gene transfer” process from bacteria to create many of today’s GMOs.

Now, as a new study shows, horizontal gene transfer in nature has likely modified some of the very crops we eat without any human input at all. Nearly 300 samples of human-grown sweet potatoes, as well as some wild ones, contain bits of DNA originally found in some of the very bacteria that inspired genetic modification, researchers reported this week in Proceedings of the National Academy of Sciences. Their findings suggest we might rethink how “unnatural” GMOs really are.

Tina Kyndt of Ghent University in Belgium and colleagues had originally set out to study sweet potatoes’ genomes for signs of viral diseases. In the course of doing that, the researchers identified some genetic material that matched DNA sequences from a type of bacteria called Agrobacterium. To figure out how common this occurrence was, they decided to study a wide range of both wild and human-cultivated varieties.

The bacterial DNA sequences ended up appearing in the genomes not only of some wild sweet potatoes, but in the genomes of virtually all human-cultivated varieties, the researchers found. This suggests that the bacteria, in the course of transferring that DNA, might have given the sweet potatoes a trait that farmers found desirable.

It’s not the only example of horizontal gene transfer in nature. As the researchers describe in their new study, some fungi have transferred coloration genes into aphids that makes those bugs green. In another instance, some ferns likely learned to thrive in low-light conditions by “borrowing” genes that make light-sensing proteins from mosslike plants called hornworts.

So the idea of genetic modification isn’t really all that unnatural. If anything, scientists borrowed one major way of doing it from nature. Scientists looking to genetically modify crops in the lab ended up adapting the Agrobacterium‘s own process of gene transfer.

Not all GMO crops are made using the Agrobacterium-based method. Other methods of genetic modification involving different molecular machinery and pathways exist, too. Sometimes, tools such as “gene guns” are used; this method eliminates the need to infect the plant cells with bacteria.

And none of this means we shouldn’t test GMOs to see how they differ from their non-GMO counterparts. There’s always that chance that a gene we introduce to a plant may inadvertently cause problems. But all the GMOs currently on the market in the United States have been tested (though exactly what sort of testing should and shouldn’t be mandatory is a source of controversy among activist groups). And scientific authorities have concluded that the GMOs on the market now probably aren’t any riskier for your health than their non-GMO counterparts.

The broader point here, however, is that even the crops we think of as non-GMO (including “conventional” and “organic”) aren’t necessarily free of genetic modification — the main difference lies in what’s doing the modifying. As Ghent University researcher Godelieve Gheysen, one of the study co-authors, said in a statement, that difference carries an important implication: “In comparison to ‘natural’ GMOs, that are beyond our control, human-made GMOs have the advantage that we know exactly which characteristic we add to the plant.”