The fundamental challenge of retrospective assays. The vast majority of HSC assays require destruction of the initial cell state to perform either a functional or a molecular assay. Establishing that a cell population, being the “soil,” contains an HSC, the “seed,” necessitates lengthy functional assays but also destroys the seed in the process. Once the presence of an HSC has been established, the cell is no longer present, and the molecular program of similar cells isolated at the same time cannot easily be distinguished from other non-HSCs profiled at the same time.