We continue the experiments which started in chapter 47. Experiments start when CA-1 reached steady state (a solution), and CA oscillates at a period = 46. Cells on the rim are short lived, while the inner cells live for ever and 'accumulate age'. Although CA structure maintains steady state, age structure does not. Core age continually increases. The lower graph depicts two age distributions. While core age rises, cell age at the edge oscillates about a constant value.
The following experiments started 200 time units after the zygote was planted . Then 'max age' was lowered. When this happens cells with ages greater than 'max age' die. Max age lowering is a way to reset the internal clock of the cell. Each experiment was repeated many times In each round the response of CA to a given 'max age' was investigated. Many CA died, other became chaotic. The lower image depicts three interesting examples. At max age = 164. CA cells in the core started dying. Then a cell in the middle, which looks like a zygote, took over and generated a new CA. It is a stem cell and not a zygote. Zygote is a cell whose color is gray ( = 1) and age = 0. . Such a cell appears only in the beginning of the experiment. A stem cell inherits its age from its parent of the previous state and its age > 0. The stem cell generates a new CA whose age structure differs from that of a zygote generated CA. (compare with chapter 37). At max ages = 177 and 201 the CA split respectively into two and three CA.
First let's distinguish between CA appearance, or somatic structure, and its age structure. Two isolated processes with the same somatic structure may differ in their age structures. This difference can be assessed when the process is challenged. In previous experiments, CA was challenged by injuring its somatic structure (v. chapter 25), here we injure (change) its age structure. Elevating cell's age advances it closer to max age, when it dies. Lowering its age makes it younger. In both cases the outcome may vary since it depends on the somatic structure.
Programmed cell death is called apoptosis. Cells in the body are programmed when to die .Lowering of age max induces apoptosis in the CA, which leads to CA death, or the creation of a new process. In the embryo apoptotic cells are replaced with invading stem cells, which generate new organs (processes).
zygote -> effect[1, 1000]; go; storeparams; restoreparams; effect[1.mm]; go