What can Y-DNA analysis reveal about the Scottish Hay noble lineage?

The family name Hay (plus associated spelling variants) is a prominent Anglo-Norman-in-origin surname that has been well-documented as a Scottish noble lineage since the 12th century CE. Their historical significance, linked to the rise in the Anglo-Norman era (1093–1286 CE) in Scotland, and the historical complexities of surname adoption post-Norman conquest of England, justifies the need for a comprehensive understanding of the genetic history of the Hay noble lineage. This study focuses on examining the patterns of paternal inheritance in lineages with the Hay surname. We conducted a comprehensive analysis of Y-chromosome data that is publicly available on the Family Tree DNA (FTDNA) platform, and specific FTDNA surname projects, as well as looking in more detail at three well-documented male-line descendants of William II de la HAYA, 1st of Erroll (d. 1201) that have been verified to a high degree of confidence. Our results reveal that all descendants of William II de la HAYA, 1st of Erroll (d. 1201) derive from the multigenerational Y-SNPs R1a-YP6500 (plus equivalent SNPs BY33394/FT2017) and R1a-FTT161. Furthermore, subclades of R1a-FTT161 have been identified that confirm direct male-line descent from two of William II de la HAYA’s sons. Subclade R1a-BY199342 (plus equivalents) confirms direct male-line descent from David de la HAYA, 2nd of Erroll (d. 1241), and subclade R1a-FTA7312 confirms direct male-line descent from Robert de la HAYA of Erroll. The result also confirms that the Hay noble lineage shares the Y-SNP R1a-YP4138 (estimated to have occurred in 832 CE) with several non-Hay test takers that have surnames of Norman origin, therefore providing further evidence to support the Norman origin hypothesis for these surnames. In addition to the identification of multigenerational Y-SNPs associated with documented Hay noblemen, this study has observed significant Y-DNA haplogroup diversity among males with the surname Hay (plus associated spelling variants: Hays, Haye, Hayes, Hey and Haya). Our results show that only 22% of the men sampled (n = 109) with the surname Hay (plus associated spelling variation) are descended from the 12th-century progenitor of the noble Hay lineage of Scotland. Therefore, this confirms that a significant proportion of males with the surname Hay do not descend from the noble progenitor of the Scottish Hay lineage of Erroll.