Self organization creating complex structures is well known in chemistry!
“Far from thermodynamic equilibrium, many precipitation reactions create complex product structures with fascinating features caused by their unusual origins. ….’
https://advances.sciencemag.org/content/2/8/e1601144.full
Wow. How does a brain (or even a kidney or pancreas) self-organize? I’ll give you TRILLIONS of years, and it will never happen, without pre-existing intelligence.