For both species, family members share some, but not all, of their lineages. Lineage membership was determined using metagenomics samples with >70% lineage-level assignment. Jaccard distance was chosen because this metric is not sensitive to differences in abundance, and values were calculated using all lineages found across samples for each subject. Distribution of within-family (green,n =17 for C. acnes, 13 for S. epidermidis) Jaccard distances is significantly lower than different time points from the same subject (red,n =27 for C. acnes, 11 for S. epidermidis). Sharing between non-family members from the same school (black,n =154 for C. acnes, 92 for S. epidermidis) is exceedingly rare.
