A question for neutral monism

Here is a kind of monism that was mentioned:

The world is composed of just one kind of substance, and its essence has both physical and phenomenal or protophenomenal attributes (alternatively: the one kind of substance is neither physical nor mental, but but the physical and mental are composed of it).

If this is the case, why does this stuff start behaving differently once brains show up? The AFR is supposed to show that the mental qua mental causes things to happen that wouldn't happen otherwise if matter simply obeyed the laws of matter. Because of the reasons that I have for acting, the protons, neutrons, and electrons in my body and elsewhere go to different places than they otherwise would go. Starting from the Big Bang through the formation of stars and planets, is there any evidence that the "one kind of stuff" has any mental characteristics? It looks pretty mechanistic to me before life emerges.

If theism is true, we can see a stable physical world as a backdrop for the creation of intelligent life. If neutral monism is true, why is everything so darn physical before life emerges?