1. We will accidentally evolve beyond the need for arms, which will shrivel up and fall off. Then we won't be able to cover our coughing, dry our hands, or pull up our own pants, and the resulting germ parade will destroy our species and monkeys will inherit the earth.
2. Paper towel dispensers will become sentient, enslave humanity, and dry off the entire world.
It's either monkeys or towels.
Whether we're fighting for more time or fewer germs, our capacity to pervert new technology always seems to eclipse our respect for it, and we end up with lamps that can turn on and off because we clap our hands at them, or antibacterial soap so strong it could eat the bark from a tree. It's no wonder aliens are trying not to be noticed. They don't want to be caught gawking.