“If the nature-over-nurture idea that your personality is not your own hard-earned creation but a product of your genes makes you feel uneasy, how about the concept of a personality composed by the bacteria living in your gut? Mice without gut microbes are antisocial, preferring to spend time alone rather than with other mice. Whereas a mouse with a normal microbiota will choose to meet and greet any new mice added to its cage, germ-free mice stick with mice they already know. Simply having gut microbes seems to make them more friendly. Beyond friendship, it’s possible that your microbiota may even affect who you are attracted to.”