&gt; If gut flora is environmental, then that&#x27;s a no-go since we span 5 states.<p>Its environmental, but one of the key environments for transferring them is mother-to-child, particularly at birth.<p>A lot of things that are environmental rather than genetic are shaped particularly strongly by the <i>early</i> (prenatal, perinatal, or early childhood) environment, which can confound efforts to intuit the degree to which a feature is genetic vs. environmental based on unstructured observations of the degree to which it seems to be associated with families.