I suggest that a new set of brain structures evolved during hominid evolution, turning the output from more primitive sensory areas of the brain into what I call a "metarepresentation." I think they edited, enhanced and packaged sensory information into more manageable chunks, used for juggling symbols and language. And most important, they made the link to meaning--whereby the sensory objects we perceive evoke multiple parallel implications in our minds. For example, an apple has potentially infinite nuances of meaning for humans, such as baking, keeping the doctor away, tempting Eve. But for a lemur, apple has no "meaning"; it's simply identifiable as food.

I believe the anatomical structures involved in creating this metarepresentation include the inferior parietal lobule, Wernicke's language comprehension area and the anterior cingulate cortex. Find out how these structures perform their job and we will have figured out what it means to be a conscious human being.

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