The human brain is at the top of the head, behind the forehead. The brains of other animals are behind their faces. Compared with the brain of an animal, the human brain has became enormous and room has had to be found somewhere for it. It is the size of our brain that more than anything else distinguishes us from other animals.
Across the millions of years evolution, the topmost section of the brain has grown so much that it has doubled over upon itself forward instead of growing straight up. The human skull, therefore, has had to grow forward to contain it. The skull grown over the face unlike other animals whose skulls are entirely behind their faces.