Food has become a battleground, and one of the fiercest fights involves genetically modified organisms, or GMOs. With the aid of genetic engineering, we have created corn, soybeans, cotton and other crops with specific genes that help them resist pests, diseases and herbicides. Supporters trumpet the reduced costs and increased yields, especially in the developing world. They also point to the ability of GMOs to prevent diseases from ruining entire industries, such as Hawaiian papayas and Florida oranges.

“When we put a gene in a plant, we know exactly where it goes, we know what it does and we actually can measure on a whole genome basis if it affects any other gene,” argues Robert Goldberg, a plant molecular biologist at the University of California, Los Angeles.

Detractors argue that GMOs raise a number of thorny issues, from medical safety to environmental protection to lax regulations and corporate control of the food supply. As the debate rages on, it’s estimated that 70 percent of processed foods already contain some modified products. Syrup from GM corn and sugar from GM sugar beets are used as sweeteners, while GM canola and cottonseed provide cooking oil. Now about 25 states across the U.S. are considering laws that would require labeling for all GM foods, so that consumers can decide for themselves.

For the health-conscious, the prevailing wisdom is that natural food is the best food. But no matter what studies of GMOs say, one scientific fact is inescapable: basically none of our dietary staples are natural. Some 10,000 years ago, our ancestors picked tiny berries, collected bitter plants and hunted sinewy game, because these are the foods that occurred naturally in the wild. Then came agriculture, and with it the eventual realization that farmers could selectively breed animals and plants to be bigger, hardier and easier to manage. Here are just a few of the modern supermarket offerings that we have been genetically modifying for centuries:

Cow and Chicken

Plump white chickens belong to a domesticated subspecies of the red junglefowl of Southeast Asia. Supermarket birds are twice the size of their wild counterparts, and they lay eggs on a near-daily basis instead of a few clutches of eggs a year. Meanwhile, Holstein cows have been bred for hundreds of years to be milk-producing marvels, to the point where most milk in the U.S. comes from Holsteins. Some evidence suggests that a protein in their milk may be the cause of lactose intolerance in humans.

Kale

The ultimate hipster ingredient has been grown in Greek and Roman gardens for at least 2000 years. So have its cousins broccoli and cauliflower, while the Johnny-come-lately Brussels sprouts appeared by the 1600s. All these veggies descend from Brassica oleracea, a wild cabbage. Some of these cabbages had a mutation for longer, curlier leaves, and plants with the desired genetic traits were bred together until they became a new subspecies, kale. Breeding cabbages with larger flower buds gave us broccoli and cauliflower. The genetic changes meant that cauliflower eventually became white, while broccoli developed a long stem—and the lifelong enmity of our 41st president.

Almonds

Wild bitter almonds contain a handy self-defense mechanism to discourage pests from eating them: cyanide. A couple handfuls are enough to kill a human. Not to be outdone, the seeds of many other plants contain chemicals that break down into cyanide, including apples and apricots. As Jared Diamond writes in Guns, Germs and Steel, at some point in history, some almond trees developed a mutation so that they lacked the cyanide-producing chemicals. Humans then collected and replanted those almonds, over time breeding a nut that is sweet and poison-free.

Grapefruit

Compared to other foods, grapefruits are relatively new and somewhat bizarre. Created sometime in the 18th century, a grapefruit is a hybrid of an orange and a pummelo. The pink variety came from a color mutation discovered in the early 20th century. Around that time, technology also brought a new, faster way for mutations to occur: deliberate radiation exposure. By bombarding plants with x-rays, gamma rays and fast neutrons, scientists were able to create thousands of new plant varieties. Two of those are the Star Ruby and Rio Red grapefruit, with modified genes for enhanced color.

Corn

Corn’s wild ancestor doesn’t contain any poisons, but it isn’t very pleasant to eat. Teosinte is a small grassy plant native to Mexico, with small, hard seeds that easily disperse from a tiny cob. Over thousands of years, farmers in North America selectively bred teosinte to have a single tall stalk and large ears with soft kernels that stay on the cob, ready for us to eat. Unfortunately, this fixation on uniform corn has led to steep declines in the crop's genetic diversity, which may spell trouble for farms facing challenges due to pests and climate shifts.

Tomatoes

Some of the unintended consequences of long-term genetic modification mean we have sacrificed flavor for visual appeal. Tomatoes, whose wild ancestors were the size of berries, were bred to be big, red, round and beautiful. In the process, they also lost some of the genes that create sugars and antioxidants, leaving us with a tomato that’s lustrous on the outside, lackluster on the inside.