Note: I’ve placed this in General Questions because I believe it may have a factual answer. If not, it can be moved.
Why is it that most people gesture with their hands when they are speaking? It seems like it’s a complete waste of energy, as it contributes absolutely nothing to the other person’s ability to interpret what is being said.
Could this behavior have evolved as a distraction, making it easier to lie to someone without their knowledge?
Thanks.
It’s called gesticulating and it’s done unconsciously to help the listener understand and emphasize various points of the dialogue. A chopping motion is a gesture that might be used to create strong emphasis. Each type of gesture has a particular meaning, but none are universal. Some gestures are distracting or protective in nature. When a person puts their hands in front of their crotch during a conversation, that usually indicates some level of insecurity or anxiety. One of my favorite books on this subject is Manwatching by Desmond Morris. It’s probably out of print, but he’s got some interesting theories on this subject. It’s worth looking for.
Well, the puppets won’t animate themselves, you know.
False premise. Gestures add a great deal to one’s expression of feelings and nuances, and hence to another’s understanding of them.
Imagine watching one of those bad-ass rap videos and having the guy just sitting in a chair with his hands folded in his lap chattering away… definately won’t have the same effect.
And how would it be possible for fishermen to communicate fishing stories without some pretty big hand gestures? 
A guy from the south once told my sign language interpreter to quit waving her
hands around because he thought it distracted me.
I do a certain amount of gesticulating when I talk, and I find that there are situations in which I do it more. On stage, for instance, I move my hands a lot. Drove the director batty.
When I speak French or German, neither of which I am fluent in, my hands are all over the place. Even if I’m only saying like two words – I absolutely cannot keep them still. I think it’s not only for emphasis, but for added understanding in case, say, my American accent is too thick to be intelligible. It might also be something to fill the space when I’m searching for words.
I’ve been asked a few times if I can speak sign-language because I move my hands so much when I talk. I don’t really pay attention to it, but I have noticed when I laugh sometimes my mouth stays open in the laughing position. Is there a name for that? 
It may be a holdover from our human or even prehuman ancestors.
The flavor of the week among new parents is something called “infant sign language”. There are courses avaible all over the place for it . Babies can pick up sign language and communicate intelligibly far sooner than they can by verbal communicaion.
I gesture even when I’m not talking. It creeps people out mightily. Think “The Gentlemen” from Buffy.