you and I are 99.9 percent similar in our underlying genetic building blocks. But the microbiome—the underlying genetic material of the bacteria in our gut or hand—can differ by 80 to 90 percent. (Worth noting is that most bacteria are in your gut, though there are also 500 bacterial species in your mouth, and about the same number in your “airways”—the respiratory system; 300 million are on the skin; for women, about 150 million are in the genital infrastructure.)
