The human brain is the only thing we can conclusively say does run a general intelligence, so, its the level of complexity at which we can say confidently that its just a software/architecture problem.
There may be (almost certainly is) a more optimized way a general intelligence could be implemented, but we can't confidentally say what that requires.
>>glial+v
If something else could replace humanity at intellectual tasks we would say it is generally intelligent as well. Currently there is no such thing, we still need humanity to perform intellectual tasks.
>>Jensso+Hj
The definition of an 'intellectual task' used to mean 'abstract from experience' (Aristotle) or 'do symbolic processing' (Leibniz). Computers can now do these things - they can integrate better than Feynman, distinguish 'cat' vs 'dog' pictures by looking at examples, and pass the MCAT and LSAT better than most students, not to mention do billions of calculations in one second. And we have moved the goalpost accordingly.