What does individual diversity mean?

I have heard that humans don't have much genetic diversity. What does that mean, what if we did have it?

• I have heard that thousands of years ago the human population became very low and that because of that, we don't have much genetic diversity. How would humans be different if we did have it?

• Answer:

  Genetic diversity is related to a concept known as Hybrid-Vigor. If you take two members of the same species that are extremely opposite from one another, the resulting offspring are usually healthier, bigger, more attractive and better adapted... With humans, who have lived in isolated pockets throughout the world for thousands of years, as a whole, our genetic vigor began to wane, resulting in diseases related to inbreeding, such as hemophilia. The last century however, the onset of worldwide travel, has done wonders for the various strains of Homo Sapiens genes, and as so-called "races" mix, the resulting blends of DNA, is in the process of producing new and improved, human physical specimens...