As the demand for food and food security increases, biologists are working to make existing crops more drought-resistant, more productive and less prone to disease.

It's a practise in which farmers have engaged for centuries. But they do it naturally, by selecting crops that appeared to grow better and then cultivating them further, or by cross-breeding dairy and good beef cattle.

The process is long-winded, and it takes many years to create the perfect species with all the desired features.

In today's high-tech world, however, there's a quicker way. Genetic engineering. By way of example, and put simply, biologists can transfer a feature that makes maize A resistant to a nasty fungus, to maize B, thereby giving it that same property.

Besides economic and environmental implications, the issue of food safety is among the most controversial in the GMO debate. There are concerns about whether altered crops could prove harmful to human health, and whether the additional features in manipulated foodstuffs could have a detrimental effect on those who eat them.

To date there is no scientific proof to suggest the fears are founded, but equally, there is no hard and fast evidence to the contrary.

Against that inconclusive backdrop, the question becomes almost philosophical, because if GMO food genuinely isn't harmful to people, then scientists are going to have to prove something that does not exist. And that could be difficult.

Study: Naturally transgenic sweet

But a recent study could shed some fresh light on the debate. Scientists from Peru and Belgium have discovered that genetic modification sometimes happens quite naturally.

In cultivated sweet potatoes from the Americas, Africa, Asia and Oceania, the researchers found that naturally occurring bacteria DNA had made its way into the potatoes' genome. The DNA originated from Agrobacterium bacteria, a common plant pathogen already known for its ability to transfer segments of its genetic information. In fact, it is this very property that scientists have used in the past to produce genetically modified crops.

In all 291 cultivated potato varieties, the Peruvian-Belgian research team found bacterial genes known to aid the production of plant growth hormones, so-called auxines.

Although this genetic information was present in all potatoes, it was only actually used by one of them, which begs the question: what role does the bacterial DNA play in the life of the potatoes.

"Since the plant hormones (...) have important roles in root development, and because the production of an edible root is what characterizes sweet potato from its wild relatives, this is one of the traits we suspect it may be involved in," Jan Kreutze, leading investigator of this study and biologist at the International Potato Center in Lima, Peru, told Global Ideas.

According to the study, genetic modification might not be human invention, but a process that has occurred quite naturally for thousands of years.

"Given that this crop has been eaten for millennia, it may change the paradigm governing the 'unnatural' status of transgenic crops," the researchers write in their paper.

And can something that happens naturally anyway be harmful?