While mammals and other primates have similar highly developed prefrontal cortex, the front portion of our brains that performs "higher order thinking". This brain development allows humans to speak, problem solve, be creative, and override emotional reactions. Despite many similarities, scientists aren't quite sure what specifics differ between us and genetically similar primates, such as chimpanzees.
Yale recently published results from brain research into these differences and found that some of these differences may also explain why humans may suffer from psychological disorders. Although there are still many mysteries to uncover what makes the human brain so unique, each discovery brings us closer to better understanding it ourselves.