To what extent not ideal nature is ideal?

I have been thinking about this question for few days. As we know that Mother Nature loves creation of variation of everything. Different types of plants, different colors of same type. Different variation of same animal species. That is what makes nature fantastic, because of its variations. But I have been thinking whether this variation is fair enough? Because let’s for instance look at human. Some people are big, strong. Some are small, weak. Some have pretty good IQ, but others bad. People with benefits of this kind of can achieve more in their life than those who didn’t get rlly well. So to what extent is nature’s variation Fair ?