answer:1. Differences in groups of people aren’t just genetic. Other influences include, diet, circumstances, culture, and education. 2. You wrote “The only reason different ethnic groups appear different is because they adapted to the environment.” but that’s an overstatement. Mutations happen randomly, and though there may be some tendency for conditions to favor certain traits over others, there are also just drifting trends that aren’t because of any adaptation or selection reasons. 3. Yes diet does affect height. Yes height can be both an advantage and a disadvantage. It’s different. There are also genetic influences. All these things are true, and I don’t see what argument is to be had about it. 4. Pygmies have their advantages. If the world were all pygmies, we wouldn’t be worried about terrorist attacks, global climate change, pollution, habitat destruction, extinction of species, GMO pollution, NSA spying, nor corrupt banks and corporations trying to own the world. 5. Just because there are differences, doesn’t mean that he or popular conceptions are correct about what they are. 6. One massive error is thinking that our concept of race is an accurate description of genetic or cultural or other kinds of traits. There are plenty of sub-groups, cross-groups, and above all every person is unique, and there are plenty of counter-examples to any trend. It sounds like this person may be overstating trends in an effort to prove a way of thinking that also overstates and misrepresents the actual relationships that the examples he chooses seem to show. I’d recommend trying to remove the argumentation aspect from it. Try to have a rule that anyone who tries to say they’re right and the other person is wrong is automatically off-base and loses a point. Stick to objective facts and statistics.