Biological systems do that because they evolve. Interactions between independent systems happen due to chance changes in some of them. But the nature of the int

Biological systems do that because they evolve. Interactions between independent systems happen due to chance changes in some of them. But the nature of the interaction is not something controlled. Switch one bit of a genetic code and a whole bunch of behaviors change (the ultimate in side effects). This is the anti-Dijkstra; a system that cannot be fully reasoned about. What we're seeing in "successful" biological systems is survivorship bias. They are useful because the system they operate in happens to be such that their function is useful to the system (they are in a temporary equilibrium). And that system is not under anyone's control, nor can it be, because every tiny change in one component, or the environment they operate in, alters that equilibrium in ways we can't predict. But there's no controlling entity pushing biology towards a particular function, so this doesn't matter in nature. A computer system modeled after this would be by nature difficult to fathom and brittle to change.