What mechanism behind intelligence could only be found in the natural world but not made into a machine? That's the thought experiment I like in this arena. It

What mechanism behind intelligence could only be found in the natural world but not made into a machine? That's the thought experiment I like in this arena. It's not useful for identifying a time to AGI, but it makes me believe AGI is possible eventually. Trillions of connections in the brain? Okay, we can make networks with trillions of parameters. Body with sensory information? We can add that. Emotions via an endocrine system? Separate interconnected subsystems? All workable in some form. A pre-encoded prior of a billion years of evolution? That one is harder, but if we're working in GHz rather than 4 Hz, can we get close enough to bootstrap? In a fully materialist interpretation of the world, I don't see anything stopping AGI from being possible.