my money is on us progressively getting more and more out of shape until we lose all muscle mass and exist simply as brains in jars with a pair of eyes and fingers. what else do we need, really. that's all people do even now - online dating, online entertainment, online schooling, online communication, online work - just imagine when we get even more technologically advanced.
as soon as physical labor ceases to exist and man power is irrelevant, we're going to become exactly that.