In van Andel-Schipper’s case, it seemed that in the twilight of her life, about two-thirds of the white blood cells remaining in her body at death originated from just two stem cells, implying that most or all of the blood stem cells she started life with had already burned out and died.

Fascinating. I'd be interested in more measurements of the population structure of hematopoietic stem cells with age. It would be integrating to see if this is a purely stochastic process of lineage loss and expansion with time, or if particular lineages reliably grow faster and crowd out the competition.