GMO

 Since pre-history people have been modifying the food we eat via cultivation.  At some point we realized that we could stay in one place if we planted seeds that could feed us.  Maybe it was just coincidence or maybe more deliberate but we learned it and it enabled us to have an established place.

The crops we planted were likely the ancestors of the ones we still plant but they wouldn't have looked much like their modern counterparts, at least in many cases.  We started to modify them at some point by planting the best seeds we could.  

This led to more bountiful harvests.  Now we learned many things over the years, but it has been going on for a very long time.  This was a long process with minor successes along the way until we got to modern times and we learned how to genetically modify our foods.

The difference is we didn't do it by "natural" ways we did it via gene manipulation.  Is it significantly different than the manipulation we have been doing via cultivation?  To some extent.  We can manipulate genes for attributes that would take generations to cultivate into a crop, if we even could.  However, it is in essence another way for humans to increase and improve crops.

Is it safe?  That seems to be the issue raised by many.  The science says it is but some are skeptical of the science since much of it was paid for by the companies selling the seeds.  Still it is published and unless I missed it, much of the criticism relates to what is unknown, potentially.

If you don't want to eat GMO, that's your business but the evidence against it is primarily flawed and mostly anecdotal.  The food we eat has already been modified via thousands of years of human cultivation.. 

Its hard to see much difference.