We humans don't have enough arms and hands. Two is not enough. Once upon a time, 2 arms and 2 hands were enough, enough to throw a rock or a spear or for fishing and farming, and do everything else humans wanted, and had, to do. No longer.
Since the Electronic Age, and the invention of the cell phone, we need another arm, another hand. For texting, typing, driving while texting, drinking while texting, changing the channel on the remote control while texting. Shaving while texting. Texting in the rain while holding an umbrella.
We could use another arm, another hand, for nearly ALL the activities we do today. And, yes, with a third arm and hand you could ... TEXT WHILE TEXTING! Yes, you'll also need a second cell phone for that.
C'mon, God, give us another arm, another hand. C'mon, science, let us add another arm, another hand. C'mon, genes, give future generations another arm, another hand. Another arm, another hand. We humans need three. That's evolution, baby!