Genetic signatures of coancestry within surnames

Surnames are cultural markers of shared ancestry within human populations. The Y chromosome, like many surnames, is paternally inherited, so men sharing surnames might be expected to share similar Y chromosomes as a signature of coancestry. Such a relationship could be used to connect branches of family trees [1], to validate population genetic studies based on isonymy [2], and to predict surname from crime-scene samples in forensics [3]. However, the link may be weak or absent due to multiple independent founders for many names, adoptions, name-changes and non-paternities, and mutation of Y haplotypes. Here, rather than focusing on a single name [4], we take a general approach by seeking evidence for a link in a sample of 150 randomly ascertained pairs of males who each share a British surname. We show that sharing a surname significantly elevates the probability of sharing a Y-chromosomal haplotype, and that this probability increases as surname frequency decreases. Within our sample, we estimate that up to 24% of pairs share recent ancestry and that a large surname-based forensic database might contribute to the intelligence-led investigation of up to ~70 rapes and murders per year in the UK. This approach would be applicable to any society using patrilineal surnames of reasonable time-depth.