Talk by Dr Lara Cassidy

Summary Over the past six years the emerging field of ancient genomics has revolutionized our understanding of human prehistory. Novel DNA sequencing technologies have rendered the genomes of ancient humans as accessible as those from modern individuals, providing researchers with an unprecedented view of the genetic profiles of prehistoric populations.

Excavated near Belfast in 1855, the bones of this farmer had lain in a Neolithic tomb chamber for 5,000 years. Her DNA has now been sequenced. (Daniel Bradley, TCD)

The similarities and differences between these groups and their modern day counterparts have allowed geneticists to build a new demographic scaffold of European history, within which Ireland provides a key reference point. It is now understood that the island was a geographical terminus for two mass migrations into Europe. The first marks the beginning of the Neolithic period, where older hunter-gatherer groups were replaced by new farming societies, whose genetic origins lie in Anatolia, a major cradle of agriculture. These first farmers were the builders of many famous megalithic monuments still visible across Ireland today. The second major population influx occurred during the Copper and Early Bronze Ages, when a distinct genetic ancestry appears on the island, whose homeland lies in the Pontic-Caspian steppe region. This migration is linked to the appearance of new technologies, burial cultures and Indo-European languages in both Europe and Ireland. Dense genomic sampling across these periods of demographic flux allows us to examine the complex interplay between geography and culture in the assimilation of new peoples to the island.

Speaker Dr Cassidy attended secondary school at Our Lady’s Bower and went on to complete an undergraduate degree in Human Genetics at the Smurfit Institute, Trinity College Dublin. She was subsequently awarded a postgraduate scholarship by the Irish Research Council to undertake a PhD in palaeogenomics in the Bradley Lab at the same institute. The main focus of her project was the sequencing and analysis of ancient human genomes from all periods of Ireland’s prehistory in order to study the island’s demographic evolution. The first publication of this work (Cassidy et al. 2016) presented a new demographic scaffold for Ireland, demonstrating that at least three ancestrally distinct Irish populations have existed on the island, whose inhabitation corresponds closely to the Mesolithic, Neolithic and Chalcolithic/Bronze Age eras, with strong population continuity observed from the Bronze Age onwards. Dr Cassidy completed her PhD last year and is now continuing to expand on this project as a postdoctoral researcher in the Bradley lab.