SLC30A9 and Zinc deficiency: Although the zinc deficiency data used here may not be similar with those of the past and could also be biased due to economic states and dietary habits, these are the best data available so far to investigate the underlying selective force of SLC30A9. The significant result of correlation suggests that individuals in continents with low deficiency states are more likely to harbor H2 to perform zinc transporting than those individuals in continents with high deficiency states.