The Differences in Human & Chimp Skulls

Cranium and Brow

• The cranium of the human skull is significantly larger than in the chimp skull. This is because of the size of the human brain, which is three to four times as large as the chimp brain. This requires a larger cranial cavity that bulges forward over the eye sockets. The smaller cranium in the chimp skull is recessed behind large brow ridges. The larger human brain causes changes to other parts of the skeletal architecture as well. Despite the differences in brain size, the skull thickness in the cranial cavity does not differ significantly between the two species.

Foramen Magnum

• Meaning "big hole" in Latin, the foramen magnum is the opening in the bottom of the skull through which the spinal cord passes to enter the spinal canal. The human foramen magnum is centrally at the bottom of the skull, whereas the chimp foramen magnum is near the rear of the bottom of the skull. This more forward placement of the human foramen magnum is linked to our upright posture. The chimp has a sloping posture with its head hanging forward, angling its spinal cord back.

Occipital Crest and Posture

• The back of the human skull is round and smooth. The chimp skull has a bony crest on the occipital bone. Attached to this bone are the chimp's larger neck muscles, which support its heavy, forward-hanging head. Our upright posture, which is related to the more central foramen magnum, requires significantly smaller muscles, rendering the occipital crest unnecessary.

Jaw

• The larger human brain necessitates a larger cranium. Combined with our relatively recessed jaw, this creates a rather flattened face in the human skull compared with the chimp skull, which slopes outward and downward from the smaller cranium to the thick, protruding jaw. Additionally, the chimp skull has much larger canine teeth than the human skull. While the cranial cavity is not significantly thicker in either species, the jaw of the chimp is much heavier and thicker than in the human skull.