Why would evolution produce such an excess?

The Encyclopedia Britannica states that man’s brain “is endowed with considerably more potential than is realizable in the course of one person’s lifetime.” It also has been stated that the human brain could take any load of learning and memory put on it now, and a billion times that! But why would evolution produce such an excess? “This is, in fact, the only example in existence where a species was provided with an organ that it still has not learned how to use,” admitted one scientist. He then asked: “How can this be reconciled with evolution’s most fundamental thesis: Natural selection proceeds in small steps, each of which must confer on its bearer a minimal, but nonetheless measurable, advantage?” He added that the human brain’s development “remains the most inexplicable aspect of evolution.”