Fig. 1. The effect of spatial constraints on heterogeneity.

Cells divide and die on a regular square lattice. A cell selected for birth can divide only into an empty grid location and may accrue passenger or driver mutations. Top: simulations on varied sizes of domains, ranging from 100 cells in diameter to 900 cells, seeded with 100 cells (k_d = 1, k_p = 0) at time zero (T_p = 5 ⋅ 10⁶, T_d = 700, s_d = 0.1, s_p = 0.01). a, b An increase in domain size results in increased driver and passenger heterogeneity, with standard deviation shown (shaded colors) for ten stochastic simulations. c–g Representative snapshots after 4000 cell generations. Bottom: Identical domain size (seeded with one-third of the domain filled; k_d = 1, k_p = 0) segregated into varied number of non-interacting regions (T_p = 10⁶, T_d = 700, s_d = 0.1, s_p = 0.01, μ = 10⁻⁸). h driver heterogeneity increases with number of segregated regions. i Boundaries limit new clones from expanding beyond a single region, decreasing the average number of drivers in the population. j–o Representative snapshots after 2000 cell generations. See attached videos V1 and V2. Solid lines indicate mean value, bands indicate ± 1 standard deviation for N = 10 simulations in a, b, h, i.