hormones and receptors - what came first?

The early "hormones" might simply have been the actual catalysts of the cellular function they signaled; they might have been both signal and agent, themselves.The early receptors might have evolved, then, as helpers to those catalysts. As their effecacy improved via evolution, the effecacy of the hormone might have decreased, until the hormone itself had no purpose but to trigger the receptor. It doesn't, actually, because evolution works often by co-opting what is already present, not by creation ex nihilo. An analagous example is the construction of a stone arch - remove one piece and the whole thing fails. Yet, arches are constructed one piece at a time. How? Via scaffolds - simpler, less effective structures that are themselves able to be built piece by piece. You build the scaffold, it supports the arch; when the arch is completed the scaffold has no purpose and is removed.

What's irreducable about it? The "friction sensor" is just the same kind of tactile nerves our whole skin possesses. The hypothalamus does more than just regulate milk production. It sends and recieves signals of every kind, all over the body. Because every part you've mentioned either serves multiple purposes in the body, or is a part easily gained by simple modification of other existing parts.It's like trying to say that sight is irreducably complex because you need not only eyes to see, but a brain as well. The reason that argument is stupid is because we use our brains for much, much more than seeing.Do you see how it works, yet?