Much of the controversy around genetically modified (GM) plants is that they aren’t “natural”, and somehow dangerous. But we may want to reconsider exactly what “natural” is.

Genetic modification is a process that sometimes happens naturally at the hands of bacteria, a new study concludes. Dozens of plants, including bananas, peanuts, hops, cranberries, and tea were found to contain the Agrobacterium microbe — the exact bacterium that scientists use to create GM crops.

“Horizontal gene transfer from Agrobacterium to dicots is remarkably widespread,” the study reads, reporting that around 1 in 20 plants are naturally transgenic.

Transgenic means that one or more DNA sequences from another species have been introduced by artificial means — in other words, an organism that has been modified genetically. In unicellular prokaryotes, this is a fairly common process, but it is less understood (and less common) in macroscopic, complex organisms.

The ability of Agrobacterium to transfer genes to plants and fungi, however, is well known. Researchers have known it for a while, as they are using this exact type of bacteria to produce desired genetic changes in plants. But before researchers thought of this, the method emerged naturally.

In 2015, an impactful study found that sweet potatoes are naturally transgenic — they’ve been GM’d by Agrobacterium. This came as a surprise for many consumers, but many biologists suspected that sweet potatoes weren’t that unique, and several other plants went through a similar process. Tatiana Matveeva and Léon Otten studied the genomes of some 356 dicot species and found 15 naturally occurring transgenic species.

It’s still a rare occurrence, but 1 in 20 is too much to just chalk it up to a freak accident. “This particular type of horizontal gene transfer (HGT) could play a role in plant evolution,” the researchers say.

It’s unclear if humans may have had something to do with this. It’s possible that the horticultural process of grafting plants could have accelerated this phenomenon, leading to the exchange of genes — which would mean that humans have been GM-ing plants for millennia. It could also have nothing to do with human activity.

“We are only at the start of this,” says Léon Otten at the Institute of Molecular Biology of Plants in Strasbourg, France, for NewScientist.

At any rate, this goes to show that in the biological world, GMOs may not be as freak an occurrence as many believe. It could also have practical implications: the European Union recently mandated that its GMO regulations exclude organisms modified through “natural” processes — so if a plant could be GMO’s through “natural” processes, it would technically not be a GMO. Whether consumers will accept this or not, however, remains a completely different problem.

The study was published in Plant Molecular Biology.