Patrilocality (in which a woman moves to her mate's residence upon marriage) and matrilocality (in which women stay put and the men move) should be reflected in intra- and inter-group differences in the diversity of Y-chromosome and mitochondrial DNA sequences, inherited from the father and mother, respectively. In the Advance Online Publication of Nature Genetics, Oota et al. put this to the test by comparing Y-chromosome and mtDNA diversity in three matrilocal and three patrilocal tribes in northern Thailand (DOI:10.1038/ng711). They analysed 360 base pairs from the mitochondrial DNA first hypervariable region and short tandem repeat (STR) loci from the Y chromosome, and found that the mitochondrial DNA haplotype diversity was higher in all the patrilocal groups, whereas the Y-STR diversity was greatest in the matrilocal groups. This analysis of Thai hill tribes emphasizes how genetic diversity is influenced by complex social behaviours.