E.A. (Euan) Young, MSc

PhD thesis: Family matters - The role of trade-offs in shaping human life-histories and health (2025)

All organisms are born and die, but the parts in between are incredibly varied. Evolutionary life-history theory tells us that this diversity across species is partly shaped by trade-offs, because organisms cannot, for example, maximize both their reproduction and lifespan. However, how well these trade-offs shape some of the most important outcomes in our own lives, such as how long we live for, is less well understood. To this end, I applied a diversity of approaches to data from three unique human datasets. First, using Swiss historical data, I found little evidence for these life-history trade-offs limiting overall family sizes, despite the high birth-rates present in this preindustrial population and no strong findings of cooperation amongst siblings. However, analyzing historical data from Finland suggested that family size may trade-off against a mother’s own lifespan, at least during challenging environmental conditions, revealing one potential factor shaping human lifespan. Whether these trade-offs remain important in more contemporary populations was less evident. Using European genomic data, I found that genetic factors shaping time to maturity and first childbirth, and fertility were not associated with genetic predispositions to breast cancer, suggesting that life-history trade-offs have not led to genes underlying this particular disease. More work must be done to develop methods and broaden research across the full richness of human diversity but this thesis illustrates that by applying rigorous and novel approaches, evolutionary biology can provide some important insights into the factors shaping our journey from cradle to grave.