You’ve heard of stem cell research and its promise of a medical revolution given the regenerative abilities of stem cells. But as it turns out, identifying what a stem cell is experimentally is not at all straightforward. Stem cells have two main abilities: cell renewal (division and reproduction) and cell differentiation (development into more specialized cells). The main problem is, there is no way to experimentally test whether one particular cell can both self-renew and differentiate to make more developed kinds of cells. Much like Heisenberg’s uncertainty principle, according to which we can’t measure a particle’s velocity and position at the same time, we can’t measure both properties that constitute a stem cell. Claims that any single cell is a stem cell are therefore inevitably uncertain, argues Melinda Bonnie Fagan.
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