Interesting discussion. I have a far-out perspective on the subject, a few of you might not be surprised.

I truly believe that if a human can walk and talk to normal standards (I'm excluding the mentally handicapped) than that human has the brain power to potentially master just about any subject we currently offer in colleges. This includes doctors, brain surgeons, rocket scientists, engineers, lawyers, etc. Some subjects like art or music I'm not quite convinced because first of all, what is mastery and second of all, it seems like some people have brains that are specifically wired for this (can see a 3D image in their head and go carve it out in stone). Taking out extreme examples and just looking at the potential of people that can walk and talk to normal standards and the current state of our technology I feel confident with my claims.
First of all have any of you tried to learn a language? It takes an amazing amount of effort and time for most people yet almost every small child is able to do it. In fact, every adult is able to do it as well - potentially even faster because they are able to work harder and with greater efficiency while using books and other studying techniques - I disagree with those that say only children can learn). I feel the biggest barrier is not the government, lack of money or time or not enough brain power. I feel the biggest barrier is ourselves. I know that sounds corny but I'm talking specifically of our physiological restraints. The same ones that say to follow another person because you are convinced that doing so would improve your situation. The same restraints that tell you that you are too stupid for anything better and that doing a job you hate is your station in life. If we were to do a poll right now I wonder what percentage of the world's people enjoy their current way of making a living. How many feel fulfilled, challenged, comfortable and proud. I'm guessing that number is very low. Yet the facts are that humans have the most advanced computational system on earth. No other animal or machine is even close.
If a child it told they are stupid (which happens in most schooling environments) and that they should do this or that or that they cannot do something then eventually most will believe it. Of course there is the whole nature or nurture debate and as you can tell I am more on the nurture side. To me the nature side is fully loaded and ready to go. The brain is a 454 V8 sitting on the line with a tank full of alcohol.
The fact is, at our current state of technology, it’s probably necessary for people to under perform. Somebody has to do the dirty work. Right? In the past the people that believed that they were inferior to others would follow strong leaders and build huge armies that could easily kill off a disorganized group of thinkers. So, this is how we got to the situation we are at today. Huge brain potential but great psychological restraints.
For those that think I'm full of it let me ask you this. Let's say tomorrow you simply decide to become a lawyer. No matter what anyone said you decided that you wanted to do it. You were fully aware that you may never get to practice but that you just loved law and wanted to put every ounce of energy into it. From morning till night. Even when you were sleeping you were dreaming about law. The beauty of it... The artistic beauty. Thus, even though you were a drop-out, told by your teachers and parents that you were stupid and that you could not possibly do it you decided to dedicate the rest of your life to the study and practice of law. You currently have a wife and child (even your wife thinks your crazy) and your current job at McDonalds barely covers your expenses. You don't even know where to start! Man, is this a hopeless case or what? It’s my contention that if this man were to dedicate his life and full effort to this task that he would easily have the ability to pass the bar in less than 10 years. I have no doubt in my mind at all. I'm talking Forest Gump like effort and dedication. Think about it. This person can already speak a language and can understand tens of thousands of words and concepts at the blink of an eye. Is memorizing the US legal rules and regulations that much of a stretch in the imagination?
Look at it this way. Take this same person and transport him back in time and have him sit next to the greatest brain in the history of man, Leonardo Da Vinci. That mere McDonalds worker would in fact be the most gifted human on earth. His genius would seem to surpass Leonardo’s by several factors. Poor Leonardo would be drawing up his airplane wings and this McDonald's worker could fold a paper airplane in a minute and make Leonardo look like a fool. Am I wrong? Human genetics take a long time to evolve (tens of thousands of years) so its not like the McDonald’s worker is genetically superior to Leonardo yet he has abilities and understanding that would make him seem god-like.
I just realized I'm sounding like a motivational speaker. You can do it!

The fact is, you truly can. Most people have more than enough raw brain power to tackle our simple level of technology. If a McDonald's worker from the future came here tomorrow he would make Einstein look bad in about 15 minutes. If you don't believe me try a small experiment. Pick something easy and dedicate 100 percent of your effort toward it for one week. I think you would be surprised at what you are capable of doing. The reality is the biggest obstacle will be your own psychology. You will tell yourself that you are tired, what are you doing this for, wouldn't you rather watch some TV and eat some delicious foods, etc. Try it and watch yourself hold you back. Priceless.