Two daughter cells receiving equal shares from the mother: that's the familiar picture of division. But what if one gets almost everything and the other just crumbs? Stochastic modeling shows that sometimes unequal division is more advantageous.
Each cell stores a protective reserve that helps it weather hardships. During division, this reserve is distributed between daughters. If the environment is shared by all cells, weak common influence favors equal division. But when common fluctuations are strong, it's better to give one daughter about eighty percent and the other twenty. The shift to such unequal division happens abruptly, like flipping a switch, not gradually like turning a dial.
The reason is that the shared environment affects everyone equally, but unequal inheritance reduces sensitivity to collective fluctuations. Even if the protective mechanism or memory of the reserve changes, the unequal branch persists, though its boundaries shift. Thus, a simple division rule explains why asymmetry in inheritance is found in living nature.
as written by the authors arXiv:2608.13370v1
Environmental sharing changes the value of diversification even when the marginal statistics experienced by each lineage remain unchanged. A minimal model of cell division couples this effect to the inheritance of a conserved protective reserve. Each mother partitions its reserve between two daughters, and each fixed partition policy generates a random demographic operator whose top Lyapunov exponent determines long-term growth. Weak environmental sharing favors symmetric inheritance, whereas sufficiently shared innovation selects a separated asymmetric branch near {\alpha \simeq 0.2}. The transition therefore occurs by a finite branch crossing rather than by a continuous departure from equal partition. The asymmetric phase persists when the protection law or reserve turnover is changed, although its boundary depends on protection nonlinearity and reserve memory. Because shared and private environmental innovations have identical marginal statistics, the mean reproductive operator is independent of the shared-innovation fraction. A dominant-mode second-order approximation then separates the asymmetric advantage into a mean-operator growth cost of specialization and a reduction of sensitivity to collective fluctuations. This approximation predicts the finite asymmetric branch selected by the full random-operator dynamics, while the full operator product determines the numerical crossing. Environmental sharing can therefore drive symmetry breaking in the inheritance of a conserved protective resource when the loss of diversification between lineages increases the value of diversification generated at division.
Asymmetric cell division is observed in stem cells: one daughter remains a stem cell, while the other becomes specialized.