The term “GMO” typically refers to crops or animals that, through genetic engineering, have had a gene (or a few genes) from a different species inserted into their genome. This is by design to improve a crop or animal with genetic engineering. In fact, me and my colleagues recently published a paper on this very topic that addresses this very topic and gives more details on the plant selection practices used for GE crops.
However, you pick up on something very important…Mother Nature, not to be outdone by humans, is also a rich source of “genetically modified organisms.” For example, the sweet potato! Layla Katiraee discusses this discovery in her blog on Biology Fortified, “Natural GMOs: The Sweet Potato.” More scientifically, long before plant scientists discovered that the soil bacterium, Agrobacterium, can be used to insert genes into plants (the main method to make GE crops), natural processes had already resulted in genes from Agrobacterium being inserted into plants, like sweet potatoes. You can read more on the science in this publication Kyndt et al, 2015.
Virtually all of the sources of food in our diets are from “genetically modified organisms.” Ancient farmers developed crops like wheat, rice, potatoes and maize. For example, wheat was created by humans breeding three different species that, if left to nature, would not have cross-bred. Fortunately, these farmers figured out how to make wheat since we enjoy the many tasty products from wheat, like French bread and Italian pasta. I recommend this blog article by Dr. Wayne Parrott for more perspective on this topic!
Plant and animal genomes are constantly undergoing changes that activate, inactivate, insert or delete genes. Humans have used this genomic diversity to domesticate many plants and animals for food production. The genomic changes in GE crops (aka GMOs) pale by comparison to the extensive genomic changes that farmers have, and continue, to make through conventional breeding practices, or that Mother Nature uses to generate the wide diversity of life on Earth.
As for a drawback or downfall, agriculture is innately impactful to our earth, so farming innovation, particularly crop technology is essential to help mitigate these impacts. Given the 20+ years “of safe cultivation of GE crops and consumption of foods/feeds from those crops” – it is now clear that the “downside” has been depriving the world’s food supply of this technology in a timely manner. We are missing out on environmental benefits as well as opportunities to give developing countries tools to efficiently grow their crops and effectively use limited resources.