I happen to know a toxicologist (someone who deveops chemicals and tests them to see if they are safe.) personally. She is a friend of my grandmother, and is considered one of the best in her field, as well as an international expert on teratology (the study of how outside influences can effect developing animals) , particularly how chemicals effect people as they grow up, starting from before they are born. She's not any smarter than 90% of the people you know. She's not stupid by any stretch of the word, but she got where she is by working incredibly hard her whole life.
Yes, some people have an edge over others when learning certain things, how much of that is how you where brought up how much is genetic is anyone's guess (smart parents may just be more likely to raise their children to be smart.) Yes, there are stupid people as well, but for the most part it is about how interested, focused, and hardworking you are.