First, let's start with a bit of an explanation or definition to narrow down what we're talking about. GMOs are essentially living organisms who's genetic material has been altered. Some could argue that selective breeding over the centuries are, in essence, a form of GMO. In our little discussion, let's exclude that definition and narrow it down to the process of either changing a gene within an organism, or adding a gene from another organism to create a modified version of the original, normally in a lab.
Now GMO isn't anything new, really. The first GMO organism was a mouse in 1974. The first GMO plant in 1983. So doing the genetic modifications and research isn't new, but it's becoming more and more mainstream and widespread. GMOs are common points of research relating to bacteria, fungi, viruses, etc. and I don't think modern medicine would be what it is without GMOs.
I think the vast majority of the fear came from the idea of "playing God" concept with plants and animals. I get that. It's rather creepy thinking of somebody in a lab playing with the genetic makeup of a plant or animal that's been through centuries of evolution. That part of the GMO equation is more of a personal belief and not really the topic of this discussion. For those personal reasons, many people stay way from GMOs. That ethical conundrum is beyond the scope of this discussion.
When relating to plants, it's worth looking at a few examples of the good and bad of GMOs. The best positive example I can think of is Golden Rice. Golden Rice started being developed when people realized in many third world countries people were dying of malnutrition and specifically a Vitamin A deficiency. Work was set out to find a solution. Since many of those countries grew rice as a staple of their diet, genetic engineering focused on adding beta-carotene to rice. Golden Rice was produced. The best part of Golden Rice is that there is no royalty or license paid to the people who developed it. Syngenta even continues to work on Golden Rice releasing v2 in 2005 with a massive improvement in beta-carotene levels. Millions of people benefited from Golden Rice in underdeveloped countries. I would call that rather successful.
Now there are arguments against it. Greenpeace for one, hates it. First, some argue that the people should grow other crops naturally high in beta-carotene instead. Perhaps, but these people already knew how to grow rice. They had the infrastructure, the fields, they know the crop, and it's already a staple part of their diet. Rice transports easily and has a long shelf-life unlike carrots. That made rice an easier avenue to give the added nutrients to the people. Some also say that Golden Rice prevents people growing the diversity of rice that they used to. The reality is the diversity is dropping with or without Golden Rice. Farmers need yield to make money and feed people. They would just as easily select a strain of rice with high yields and plant all their fields with that thereby creating a monoculture of another sort. I agree the diveristy is being lost, but that's a factor of economics, not GMOs.
Let's look at field crops like Corn, Canola, Soybeans, and so forth. When you grow these large staple crops, one of the hardest things to control in the fields are weeds. Home gardens, we just hoe them or pull them out, but when you have over 2000 acres of corn, that really isn't an option. Enter herbicides. Controlling weeds in corn needed a very large number of herbicides and, at the time, some of them had an extremely long persistence in the ground. Take the old Atrazine which was extremely common (and probably is still used around the world). They say for every pound of atrazine per acre you applied, you could not grow corn for one year. The maximum rate was 7lbs/acre. That means nothing else except corn would grow for seven years. Ouch.
Enter RoundUp Ready Corn - a GMO corn that was developed by Monstanto (I think soybeans were actually first, but I'm using corn in this example). In this case, the plant was genetically modified to metabolize glyphosate. Relative to atrazine, RoundUp or glyphosate is way more benign. You can plant almost anything into a field two weeks after you sprayed glyphosate. Not only that, very few weeds escaped glyphosate compared to atrazine so even more chemicals were used if you didn't use RoundUp. The advent of RoundUp Ready crops reduced the use of pesticides dramatically and allowed farmers to use far safer products increasing their own personal safety. Knowing all the concoctions used before RoundUp Ready corn came out, I would personally gladly eat the GMO corn instead.
Enter the world of economics and politics. Monsanto was a company and, as all companies, wanted a profit "for the benefit of the shareholders". Monsanto owned the patent on RoundUp and the patent on the GMO seed. So every seed produced a kick-back for them. A business practice you can't really fault them for since that's what any business would do with any other product. Every pesticide used on those crops also went back to them. Good business model, but disconcerting when one company holds so much power over staple food crops. Farmers could no longer collect and save their own seed since that was patented. They had to buy their RoundUp Ready seed every year from Monsanto. It did make the seed more expensive and locked them into one source, but it did overall make that crop safer for the farmer to grow and reduced overall pesticide applications. Farmers did have a choice and could still grow conventional crops and some did.
Then another problem happened. Some of those conventional farmers grew their soybeans near another farmer that grew the RoundUp Ready soybeans. They cross-pollinated. The seed from the conventional grower now contained the patented gene from the RoundUp Ready one. Ouch. You can see here where the politics and economics rears it's ugly head with laywers getting involved and law suits abound. This created the biggest negative press possible, with some validity, bringing GMOs into the spotlight and raising all kinds of questions. People brought up the evil corporate empire theories and that mutated into safety issues, possible health side-effects, and so on and so forth.
So are GMOs good or bad? Are they safe? Like anything, GMOs were developed to try and solve a problem. Some of them did it freely for the good of people like Golden Rice. Some wanted to make money on their efforts to reduce pesticides and make farming safer. Personally, I don't think GMOs are bad. Imagine a GM Elm tree resistant to the Dutch Elm Disease, or an Ash tree unpalatable to the Emerald Ash Borer. That would be good. I may not agree with all the business practices or pricing scales, but they solve some very valid problems and there have been many benefits to GMOs, especially the "under the radar" aspects in medicine.
The question that's probably on everybody's mind is if the seeds and plants sold in garden centres are GMOs. I think I can say with 99.99% confidence that nothing is genetically modified in the garden centre. Development on GMOs is based on larger scales of production. With fruits and vegetables and flowers, it's way easier to develop new varieties and fine-tune a trait by cross-pollinating, selective breeding, or opportunistic breeding isolating random mutations. They won't be pesticide tolerant nor would they add in nutrients not found naturally, like GMOs, but that probably isn't really financially viable for researchers. Plus, I think most breeders would be afraid of the fear and negative connotation around GMOs. So rest easy, plant your tomato, and enjoy the fruits of your labour. And also remember that millions of people are alive and healthy in the world thanks to Golden Rice.