The brain unfolds during development, by means of essential cell:cell interactions, of which we understand only a tiny fraction.

FORBES: What's the Likelihood of the Singularity? Part Two: Uploading the Brain

And we have absolutely no way to calculate in principle all the possible interactions and functions of a single protein with the tens of thousands of other proteins in the cell!

FORBES: What's the Likelihood of the Singularity? Part Two: Uploading the Brain