Arterial partial pressure of oxygen ( pO
a ). Partial pressure evolves with fluctuations until the optimal value is achieved. The figure shows the dynamics of the first 200 iterations until the system adapts (when the frequency of chemo receptors fall to zero). For each animal maturation takes place in a given time T, since 1,000 iterations were run, the unit is T/1,000. This comment applies to the rest of the figures.