Figure 4. Irreversible differentiation can evolve if organism grows to a large enough size in the course of its life cycle.

(A) The fraction of composition effect profiles promoting irreversible strategies at various cell differentiation costs ($c=c_{s\to g}=c_{g\to s}$) and maturity sizes ($2^n$). Irreversible strategies were only found for maturity size 2⁶ = 64 cells and larger. (B) The fraction of composition effect profiles promoting irreversible strategies at unequal differentiation costs $c_{s\to g}=2c_{g\to s}$. A rare occurrences of irreversible strategies (∼1%) was detected at the maturity size $2^5=32$ cells in a narrow range of cell differentiation costs but not at the smaller sizes. (C) The range of cell differentiation costs allowing evolution of irreversible strategies at at the maturity size $2^n=32$ ($n=5$) cells. For irreversible strategies to evolve at such a small size, the differentiation from soma-role to germ-role must be much more costly than the opposite transition ($c_{s\to g}\gg c_{g\to s}$).