I've been fascinated by fetal development and cellular signaling and it is brutally complex when you get down to the level of cellular receptors and signaling cascade chains, dna expression, etc. You have signals signaling signals, hormonal triggers, electrolyte triggers (i.e. calcium) and multiple pathways, feedback loops, etc. I'm amazed these all function and we are alive when you look at it all.

I wonder how many of these systems are really necessary and just reflect the random progression of evolution or do they represent a hardiness that comes from redundancy?

To develop medications that work on one of these pathways is a huge challenge. You'd not only have to track the ramifications of modifying the pathway but how all the other ones and various feedback systems would respond in kind. On top of that you can have the same receptors and signaling proteins used for different systems around the body, they are only differentiated by cell type and physical isolation (diffusion limits), so you can't just pump a drug into the blood stream without affecting "innocent bystanders" (i.e. serotonin drugs).

One more thing, it is amazing how much is controlled by the hypothalamus and brain stem, the most primitive parts of the brain. It must reflect its early origins and how basic these systems are. The cerebellum and cerebrum, by virtue of their external physical locations, can grow or modify more freely without much limitation but the hypothalamus and related structures, have to pretty much stay constant in their basic structure and functions. It is surprising to see that a cluster of neurons (KNDy) would be behind this process but I really shouldn't be. It is no coincidence the pituitary is so closely linked physically and chemically to that region.