curiosity is the part of our nature which makes us try to understand why things happen. it is what lead to our first logical thought and reasoning ability. and by finding out why things happened, we were able to recreate those causes; giving us tools and fire. without curiosity we would not learn, and therefore would revert to pre-tool-using form of ape behaviour.
I think even apes have some curiosity, they just do less with it. Young animals are especially curious, and they learn a lot faster than older animals. Once you think you know it all, thinking grinds to a halt Please Register or Log in to view the hidden image!
It is a tool for survival and it is not limited to humans. If you don't check things out, you'll never learn anything.