For thousands of years, humans have been genetically enhancing other organisms through the practice of selective breeding. Look around you: the sweet corn and seedless watermelons at the supermarket, the purebred dogs at the park, and your neighbor's prize rosebush are all examples of how humans have selectively enhanced desirable traits in other living things.
Farmers throughout history have been raising their plants to achieve certain desired traits such as improved taste, yield, or disease resistance. 
But this kind of breeding still relies on the natural reproductive processes of the organisms, whereas genetic engineering involves the addition of foreign genes that would not occur in nature. Since several common ingredients like corn starch and soy protein are predominantly derived from genetically modified crops, it's pretty hard to avoid GM foods altogether.
In fact, GMOs are present in 60 to 70 percent of foods on US supermarket shelves, according to Bill Freese at the Center for Food Safety; the vast majority of processed foods contain GMOs. One major exception is fresh fruits and veggies. The only GM produce you're likely to find is the Hawaiian papaya, a small amount of zucchini and squash, and some sweet corn. No meat, fish, and poultry products approved for direct human consumption are bioengineered at this point, though most of the feed for livestock and fish is derived from GM corn, alfalfa, and other biotech grains. Only organic varieties of these animal products are guaranteed GMO-free feed. While 90 percent of corn grown in the United States is genetically modified, most of that crop is used for animal feed or ethanol and much of the rest ends up in processed foods.
Sweet corn—the stuff that you steam or grill on the barbecue and eat on the cob—was GMO-free until last year when Monsanto rolled out its first GE harvest of sweet corn. While consumers successfully petitioned Whole Foods and Trader Joe's to not carry the variety, Walmart has begun stocking the shelves with it without any label. While the majority of squashes on the market are not GE, approximately 25,000 acres of crookneck, straightneck, and zucchinis have been bioengineered to be virus resistant. Be wary of the "All natural" foods label if you're trying to avoid GE foods. 
Right now there is no strict definition of what constitutes a natural food.
This could be changing soon as federal court judges recently requested the Food and Drug Administration to determine whether the term can be used to describe foods containing GMOs to help resolve pending class action suits against General Mills, Campbell Soup Co., and the tortilla manufacturer Gruma Corp. In 1995, Monsanto introduced genetically modified potatoes for human consumption, but after pressure from consumers, McDonald's and several other major fast food chains told their French fry suppliers to stop growing GE potatoes. The crop has since been removed from the market. While it would seem plausible that a fruit that produces no seeds has been bioengineered, the seedless watermelon is a hybrid of two separate breeds. It has been nicknamed the "mule of the watermelon world."
Currently no meat, fish, or egg products are genetically engineered, though a company called Aqua Bounty has an application in with the FDA to approve its GE salmon. Scientists conducted the first GE food trials the late 1980s, and in 1994, a biotech company called Calgene released the first GMO approved for human consumption: the "Flavr Savr tomato," designed to stay ripe on the vine longer without getting squishy. The product, which Monsanto eventually picked up, flopped, but it paved the way for others: Biotech companies have made billions since with GE corn, soy bean, cotton, and canola. In Part 3 on my next post, I will discuss how people are fighting back to protect our food supply. Feel free to leave comments and be sure to hit the “Like” button at the bottom of this post.
