There has been an ongoing controversy about the simultaneous dangers and wonders of GMOs, or genetically modified organisms. If you live in the US, you have almost certainly not escaped eating such genetically modified foods, probably mostly in the form of fruits and vegetables. (Although most meats themselves are not yet genetically modified, the corn and soy that compose their feed are.) In fact it can be hard to find produce that is not modified as 95% of beets, 94% of soy, and 88% of corn contain proteins that were engineered to be resistant to insects for herbicides. But the truth is that such selection for specific traits happens naturally in species and to date there have been no studies that show significant detrimental consequences to humans from eating genetically modified foods.
One thing to bear in mind is that nowadays when people talk about GMOs we're usually talking about transgenic organisms, where genes from one organism are extracted and fused into the genes of another organism to give them some specific trait. This practice of transgenics is by no means a new technology. One of the first FDA approved transgenic plants was called the Flavr Savr Tomato, which was altered so that it would take longer to ripen and could therefore be shipped around the country. Unfortunately, the Flavr Savr didn't actually do what its name might suggest and never took hold in the market.
More so than the scientific reasons, much of the controversy behind GMOs hangs in the cultural and economic consequences of placing so much power over our food supply in the hands of the monopolies that control GMOs and the herbicides (Roundup) that spur their growth. Because of this, the GMO debate is often a proxy for the even bigger debate against large companies with unporportional power.