The logic behind comparing surnames and Y chromosomes is elegantly simple. Because both are transmitted from father to son, two men sharing a rare surname should, more often than not, also share a similar Y-chromosome profile, especially if the surname arose once in a single founder. This principle has powered famous forensic and genealogical successes, from confirming the remains of the Romanov family through Y-DNA analysis to demonstrating genetic coancestry among British men sharing the surname Sykes. Studies of the Cohen modal haplotype among Jewish priestly lineages and the genetic legacy of Genghis Khan’s male descendants in Asia have similarly exploited the parallel inheritance of names and Y lineages. In Europe, particularly in Britain and parts of Germany and Italy, researchers have repeatedly found that surnames carry detectable Y-chromosomal signatures, a phenomenon sometimes described as surname-associated genetic strata.

The Argentine Northwest, however, presents a very different demographic history. The region encompasses the high Andean plateau of the Puna, the Quebrada de Humahuaca, and adjacent valleys in provinces such as Jujuy and Salta, areas where Indigenous communities have lived for millennia and where Spanish colonization from the sixteenth century onward layered a new system of names, kinship, and settlement over existing populations. Earlier work by several of the same authors, including studies of isonymy, the analysis of surname sharing as a proxy for genetic relatedness, had already documented complex patterns of surname adoption, change, and mixing in historical parish records from towns such as Casabindo and Cochinoca. Colonial registries reveal that Indigenous individuals frequently acquired Spanish surnames, sometimes through baptism, sometimes through labor obligations, and sometimes through informal assignment, while genealogical surveys in Argentina have previously shown unusually high rates of non-paternal surname transmission compared with European populations.

To quantify how much these historical disruptions have scrambled the surname-to-gene correspondence, the team genotyped a panel of sixteen Y-STR markers in each of the 232 men, producing a haplotype for every individual. Y-STRs are stretches of DNA in which a short sequence repeats a variable number of times, and because these repeats mutate at a relatively rapid and roughly clock-like rate, they allow researchers to distinguish closely related paternal lineages and to estimate how long ago two haplotypes diverged from a common ancestor. The team also characterized haplogroups, the deep branch labels on the Y-chromosome tree defined by single nucleotide polymorphisms, which distinguish lineages of Native American origin from those of European, African, or Asian origin. This combination of fine-scale microsatellite data and coarse-scale haplogroup assignment gives both a recent genealogy and a deep history for each chromosome sampled.

The analytical toolkit was equally classical. The researchers constructed Median-Joining networks, a widely used algorithm introduced by Bandelt, Forster, and Röhl in 1999, which arranges haplotypes as nodes connected by mutation steps, allowing shared ancestors, or nodal haplotypes, to be identified visually at the centers of star-like clusters. They searched for identical or near-identical haplotypes both within surnames, which would indicate a shared paternal founder, and across different surnames, which would reveal either ancient common ancestry or, more provocatively, breaks in the chain of surname transmission. Divergence times between haplotypes were estimated using established Y-STR mutation rates, providing a rough chronology for when lineages separated.

The networks revealed a clear and evocative structure: two central nodal haplotypes, one representing a Native American paternal lineage and the other a European one, with the remaining haplotypes radiating outward from these hubs like spokes around two hubs of a wheel. This architecture reflects the region’s colonial history, in which Spanish male settlers and Indigenous men both contributed paternal lineages to the modern gene pool, a pattern consistent with the directional mating documented in earlier studies of the area, where European men disproportionately contributed to the paternal gene pool while Indigenous women contributed more heavily to maternal lineages traced through mitochondrial DNA.

Crucially, the study found both directions of correspondence and its failure. On one hand, there were cases in which men sharing the same surname also shared matching Y-STR haplotypes, exactly what the classical model predicts and a reminder that surname-based genealogy can still point to genuine biological kinship. On the other hand, the researchers identified identical genetic lineages carried by men bearing entirely different surnames, meaning that the same paternal chromosome had been split across multiple family names over the generations. The frequency of such cross-surname genetic matches suggests that the irregular transmission of surnames in the Argentine Northwest has been substantially higher than the rates reported in comparable studies from Europe and elsewhere, where the surname-Y chromosome link tends to hold together more tightly over centuries.

Why would surnames drift so far from their genetic anchors in this region? The historical record offers several converging explanations. Colonial-era naming practices in the Andes often assigned or changed surnames administratively rather than biologically, decoupling the name from any single founding lineage. High rates of endogamy and small effective population sizes in isolated highland communities meant that surnames could be adopted, abandoned, or reshuffled within a few generations. Illegitimacy, informal adoption, maternal surname retention, and undocumented paternity all break the father-to-son chain of name transmission without leaving obvious traces in parish books. Previous genealogical work by Muzzio and colleagues across Argentina documented regional differences in non-paternal surname transmission, and the new data suggest the Northwest sits at the high end of that spectrum, likely reflecting the compounded effects of Indigenous naming traditions, colonial imposition, and centuries of admixture.

The implications extend beyond genealogy into forensic science, where Y-STR profiling is routinely used to identify male perpetrators from trace evidence and to associate remains with family lines when reference samples are unavailable. The implicit assumption in some investigative genetic genealogy approaches is that a surname can narrow the search for a male relative carrying a particular Y profile. The Argentine Northwest results are a caution: in populations with turbulent naming histories, a shared surname is a weaker clue, and a shared Y haplotype may not correspond to any documented family name at all. Conversely, the persistence of some surname-haplotype matches shows the method retains real power when its limits are understood.

For population geneticists, the study is a vivid demonstration that cultural inheritance and biological inheritance, however parallel they appear on paper, follow genuinely distinct evolutionary dynamics. Surnames are subject to social rules, administrative decisions, and historical accidents; Y chromosomes are subject only to mutation, drift, and the reproductive success of their carriers. When the two trails are laid side by side, as Geronazzo, Bailliet, and their colleagues have done with unusual care in this admixed Andean population, the divergences between them become a measurable record of social history itself, capturing in genetic detail the naming practices, migrations, and mating patterns that written archives record only incompletely. In the Argentine Northwest, both trails remain blurry, but the blur itself turns out to be informative, encoding centuries of colonial encounter and cultural change in the DNA of living men.

Subject of Research: The correspondence between Y-chromosome lineages and surname inheritance in the admixed populations of the Argentine Northwest

Article Title: Y-chromosome lineages and surnames, two blurry trails

Article References: Geronazzo, A., Muzzio, M., Sepúlveda, P. B. P., Andrade, L. D., Cuello, M., Chaves, E., Dipierri, J. E., Bravi, C. M., Gómez, E. L. A., & Bailliet, G. (2026). Y-chromosome lineages and surnames, two blurry trails. International Journal of Legal Medicine. https://doi.org/10.1007/s00414-026-04006-6

Image Credits: AI Generated

DOI: 10.1007/s00414-026-04006-6

Keywords: Y chromosome, Y-STR, surnames, haplotypes, Argentine Northwest, paternal lineages, genetic genealogy, Median-Joining networks, Native American lineages, admixture, forensic genetics, isonymy