We humans are very peculiar primates. We walk upright, precariously balancing our heavy bodies on two short feet. Our heads are oddly swollen, with tiny faces and small jaws tucked below the front of our balloonlike braincases. Perhaps most remarkably, we process information about the world around us in an entirely unprecedented way. As far as anyone can tell, we are the only organisms that mentally deconstruct our surroundings and our internal experiences into a vocabulary of abstract symbols that we juggle in our minds to produce new versions of reality: we can envision what might be, as well as describe what is.
Our predecessors were not so exceptional. The fossil record clearly shows that not much more than seven million years ago, our ancient precursor was an apelike, basically tree-dwelling creature that carried its weight on four limbs and had a large projecting face and powerful jaws hafted in front of a very modest-sized braincase. In all probability, it possessed a cognitive style broadly equivalent to that of a modern chimpanzee. Though undeniably smart, resourceful, and able to recognize and even combine symbols, modern apes do not seem capable of rearranging them to forge new realities. Thus, to arrive at our own species, Homo sapiens, from this ancestor took a lot of fast evolutionary modification.