Very unclear what you mean by intelligence. Human beings are clearly of a unique order and class, so I assume that is what you are referring to, our overall complexity and ability to continually emerge new layers of complexity from previous ones. Other than that, I think these kind of questions are really left unanswered at the moment as there is too much we simply do not yet know. The areas we “know” the least about in relationship to the science we know the most about (chemistry, physics, biology) are specifically things like “intelligence”, mind, psychology, etc so it’s naive to expect answers as clear as we can get in the hard sciences here.