We have more than enough food. It's a distribution problem...
I don't mean to sound like I disagree with you, but I hate hearing this arguement being made as a reason why GMO food is not needed. I wish I could remember who I originally heard express it, but I read a reply to this argument that went something like "so instead of just a distribution problem, you would rather it be both a distribution AND a supply problem?" I would rather only have to deal with one issue because of an excess of food than just barely being able to make it with the supply we have AND assholes stealing it all as well.
Africa, for example, had more than enough food in the 1960s and 1970s
This may be true, but does that take into account the population growth since then? I really don't know. According to this first link I found from Googling "world population 1970", the world population was roughly half what it is today. Whether or not our population should be increasing at that rate is a different argument, but it is the reality.
Being a GMO food also doesn't magically induce some special extra mutation property into a plant either. A GMO plant wouldn't "diverge a great deal further" from a non-GMO unless you can propose a mechanism that would cause a higher rate of mutation due to transgene engineering.