"Oh, dear me, how unspeakably funny and owlishly idiotic and grotesque was that ‘plagiarism’ farce! As if there was much of anything in any human utterance, oral or written, except plagiarism! The kernel, the soul — let us go further and say the substance, the bulk, the actual and valuable material of all human utterances — is plagiarism. For substantially all ideas are second-hand, consciously and unconsciously drawn from a million outside sources, and daily used by the garnerer with a pride and satisfaction born of the superstition that he originated them; whereas there is not a rag of originality about them anywhere except the little discoloration they get from his mental and moral caliber and his temperament, and which is revealed in characteristics of phrasing."
-Mark Twain
Brain compartmentalizes information. Each individual is led through different experiences throughout his/her life and as such, the being develops an understanding unique to his/her own experiences and perceives the world around accordingly. As soon as we look at an object, our brain links up the relative memories and makes a coherent story from what we know, based on our past experiences. For example, when you look at a random person in the market, certain words cross your mind, the words being a function of what the person is like to you, based on your past experience, and you come up with a coherent story relating everything you just perceived.
Now, before we dwell any further, an important thing to be acknowledged by the reader here is the sense of the terms used: idea and new idea, which may be best understood by examples. An idea would be if an individual, happily so, thinks of some apparently 'new' social networking site, a car that can hover, or what not. Some idea worth implementing would be not worth mentioning here, for it will be foolish to make it available as such potentially throwing away an opportunity that may comfortably sustain the remainder of my life.
So moving on, a new idea would be to think of and accurately depict (as of now, only some guy time-travelling from the future would be able to confirm it though) a black hole, the singularity of the big bang, the events before the big bang, i.e something no one has experienced.
There is no such thing as a new idea, just indefinitely convoluted combination of various past experiences. What we feel is a new idea is, what comes when a lot of random notions from the past experiences churn together until they coalesce. No doubt our cognitive abilities are far superior than any other living thing, but we're still apes with smartphones.