I am not sure how your twin theory works but I have a couple of comments:

1. Other species do communicate verbally and with body language. I suspect the key to humans is our freakishly large brain. The need to communicate in pack animals in order to capture the prey animal would lead to spoken language if the ability to make different sounds is there and the brain to translate it.

Clearly certain birds can mimic human words but lack the brain to use them the way we do.

2. Given how twins are formed I would say it is inevitable that other species have them too.

Intersting subject!

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.