Results of genetic analyses show that social groups of female andimmature sperm whales are comprised of multiple matrilines asevidenced by the presence of multiple mitochondrial (maternallyinherited) control region haplotypes. These data suggest: (1) asocial environment in which the transmission of culturalinformation, such as vocal dialects, is more likely to be horizontalor oblique rather than strictly vertical (mother-offspring) and (2)lead us to question the data presented to support gene-culturecoevolution.