He states that the environment and embodiment are crucial for the development of intelligence. Even for humans, 'our environment puts a hard limit on our individual intelligence'.
https://medium.com/@francois.chollet/the-impossibility-of-in...
The implausibility of intelligence explosion (2017)
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In essence we need simulators on par with reality to train human-like intelligence. BTW, take a look at ThreeDWorld, just came out: 'A High-Fidelity, Multi-Modal Platform for Interactive Physical Simulation'. We're getting closer, and AI scientists are aware of the environment problem.
I have been interested in this debate for perhaps a decade now, and to me one of the most important things to get clear is whether skeptics are just claiming X is really hard, or whether they are claiming it's impossible as a matter of principle, which are two very different things. I think this discussion is about the latter rather than the former, but that many people talk about the former as if it's relevant to the latter.