Genealogical surveys show a high rate of non-paternal surname transmission with regional differences in Argentina.

Surnames are a vertically transmitted cultural trait that in Argentina follows the paternal line of descent when the paternity is known. There was a lack of empirical information regarding non-paternal surname transmissions among the general population, so we performed 2,550 genealogical interviews, which included 6,954 surname passes, in different regions of this country. We compared the proportion of non-paternal transmissions between the propositus and parental generation and found no significant difference between them (p < 0.01). Inter-population comparisons allowed us to describe 4 regional groups. We also drew models and simulations to estimate how many generations it would take to find that only half of the population maintained the paternal transmission. The lowest proportion of non-paternal transmission was 7.3%, estimating 9 generations (between 225 and 315 years) to find that, at most, half its population keeps following the paternal transmission; the highest proportion was 23%, taking 3 generations (75–105 years). Our results show a high proportion of unrecognized paternities among the general population, a very quick loss of association between male lineages and surnames, and regional proportions with significant differences between each other.