Want to bring it down to the biggest single issue? This is it: a tremendous fraction of the biological functioning of the human body is dependent on emergent co

Want to bring it down to the biggest single issue? This is it: a tremendous fraction of the biological functioning of the human body is dependent on emergent complexity. This makes it very difficult to understand precisely how and why our systems work, and orders of magnitude more difficult still to figure out how exactly to make them work differently. When you're talking about "what multi-trillion cell bodies do", it's an enormous and chaotic possibility space where "make cells age in reverse so they don't die" could require vastly different initial conditions than "make cells grow".