This is an important question and has been discussed several times on GMO Answers. You might be interested in these graphics briefly outlining the history of crop modification.
According to Dr. Bruce Chassy, professor emeritus of food safety and nutritional sciences at the University of Illinois at Champaign-Urbana, “GM crops have been planted on more than 2 billion hectares by more than 17 million farmers over 17 years in about 30 countries, with no adverse ecological impacts observed.” His full response is available here: http://gmoanswers.com/ask/are-there-studies-prove-gmos-wont-harm-my-health-long-term.
Also, Fourat Janabi discusses the history of humans modifying foods in The Lowdown on GMOs According to Science. Here is an excerpt:
The key point is that evolution happens regardless of whether we rework it to our advantage (biotech crops) or leave nature be (organic). The changes between the disparate crop-growing methods are in degree, not kind:
- Evolution is natural selection by random mutation
- Preindustrial (i.e., organic) agriculture is artificial selection by random mutation
- 20th-century (conventional and organic) agriculture is artificial selection by accelerated random mutation (mutagenesis)
- GM agriculture is artificial selection by purposeful mutation
To label one unnatural is to label them all unnatural. Recall that, as Richard Dawkins said, “no agriculture is natural.” The natural way of life for a human being is the hunter-gatherer lifestyle. Human beings have been around for approximately 200,000 years, and agriculture has been practiced for only 10,000 years. It’s quite likely there were hunter-gatherers who refused to switch to the then-“new” method of agriculture. Each of the above labels is evolution (that is, natural) continued. Something has to fulfill both the selection process and the mutation process in evolution. If we are happy to leave it at organic, then nature, which has neither direction nor purpose, and evidenced by her 3.67-billion-person death toll in the 20th century alone (from just 2 categories, no less), has neither one’s health nor one’s longevity in mind; or we fulfill the selection process, which, paradoxically to those who hold nature in high esteem, it has given us the ability to so.
While the result of recombinant DNA technology may be labeled unnatural (because it doesn’t exist in nature, not because it can’t), the same cannot be said of the technology that produces such food. We are co-opting nature’s methods to make food, not playing God. You may dispute the fact that I said that it could exist in nature by saying that a fish gene could never wind up in a tomato, but you would be betraying a fundamental concept of evolution. Nature uses the same genes over and over again in all manner of disparate creatures. There are no such thing as fish genes, tomato genes or human genes. There are only genes that perform specific functions and that operate according to the principles of natural selection. Take an example: your genome is the combined genome four times over of the amphioxus fish-like marine chordate. The marine chordate’s genome, a 1 cm little fish, has, in the course of Earth’s history, mistakenly copied over on itself twice, and those two mistakes have resulted in every land animal today, and you. If nature can turn a little fish into you (and that fish’s genome is still inside you), then why is it so distasteful that we put disparate genes where we need them? Uncertainty may be the first thing that comes to mind, but nature had no idea what she was doing either. After all, 99.9 percent of all species died out for us to be here. So it’s not like she knew what she was doing. It’s just coincidence that we are here and lucky to be top of the food chain, no less.
Some may wonder: What is the point? Well, today, there is a movement to demonize GM technology and conventional agriculture, with a concomitant wish to return to a mythical agricultural past. Organic agriculture is fine, there’s nothing necessarily wrong with it, but we can’t feed the world with it. Paul R. Ehrlich’s book The Population Bomb clearly stated in 1968 that in the ’70s and ’80s, mass famines would ensue, as we wouldn’t be able to make enough food, and any efforts to avert such a disaster are a waste of time and should be scrapped. (Thomas Malthus said the same thing in 1798.) Ehrlich wrote, “The battle to feed all of humanity is over. In the 1970s the world will undergo famines—hundreds of millions of people are going to starve to death in spite of any crash programs embarked upon now.” Why didn’t the predictions of mass starvation and disaster come to pass? Well, they would have if we listened and did nothing. Luckily, we didn’t. Instead, we developed the technologies that allowed us to increase yield to a stupendous degree to avert such a disaster. That is, we bid goodbye to organic agriculture, and yet, now that the population has more than doubled to 7 billion and another 3 billion folks [are] yet to come by 2050, going back to organics is the key? It couldn’t feed us at 3 billion; what possible solution would it be to try again at seven and ten billion?”
You can read the full article posted to GMO Answers here: http://gmoanswers.com/studies/random-thoughts-biotech.