  The emergence of complex organs is driven by the coordinated proliferation,
migration and differentiation of precursor cells. The fate behaviour of these
cells is reflected in the time evolution their progeny, termed clones, which
serve as a key experimental observable. In adult tissues, where cell dynamics
is constrained by the condition of homeostasis, clonal tracing studies based on
transgenic animal models have advanced our understanding of cell fate behaviour
and its dysregulation in disease. But what can be learned from clonal dynamics
in development, where the spatial cohesiveness of clones is impaired by tissue
deformations during tissue growth? Drawing on the results of clonal tracing
studies, we show that, despite the complexity of organ development, clonal
dynamics may converge to a critical state characterized by universal scaling
behaviour of clone sizes. By mapping clonal dynamics onto a generalization of
the classical theory of aerosols, we elucidate the origin and range of scaling
behaviours and show how the identification of universal scaling dependences may
allow lineage-specific information to be distilled from experiments. Our study
shows the emergence of core concepts of statistical physics in an unexpected
context, identifying cellular systems as a laboratory to study non-equilibrium
statistical physics.
