Well it depends on your definitions.

What signs of logic are you looking for? The fact we have a language? Animals can communicate. The fact we ponder our existance and have things such as religion? That is where I would like some answers.

Im a stout evolutionist, but I have never really given thought to this. If you look at the evolutionary chain, you've got a ton of lower-thinking life forms, and then boom! us, the acme of evolution, self-realized beings.

How was the jump made?