I think the most likely case is that the properties of a system that leads to emergent behavior (part of complexity science) are very much present in the brain

I think the most likely case is that the properties of a system that leads to emergent behavior (part of complexity science) are very much present in the brain where the various components with a proper balance leads to the intelligence we have. An interesting intelligence emerges from a colony of ants compared to one. An interesting intelligence emerges from the relations of the various parts of the brain. An interesting intelligence emerges from the combo of techniques that have led to GPT and other surprising AIs. Same with a human, to two humans collaborating, to tribes to companies to cities etc. And likely same by combining/integrating GPT-4 type of LLMs with other tools and with other specific purpose LLMs - a greater unit of significance will emerge. (The non-predictability of this with current science is what is kind of scary to me.)