Homo sapiens

Human

Your head weighs about 5 kilos.
It is precariously perched on top of a tall, bipedal body.
What are the consequences ?

Vulnerability

Because we insist on standing upright, on only two legs, the human head is especially vulnerable to injury from falling. Perhaps this is why our parietal bones are so thick ?

Upright Stance

Most animals hold their heads more or less horizontally, and if their head is as heavy as this musk ox's they need big muscles to hold it up. The human skull is unique in having the main joint with the neck only slightly behind the centre of balance so that although the main positioning muscles are those at the back of the neck, a complex network of other muscles is required to help us turn and tilt our heads. These can be seen to particular advantage in female tv presenters.

Weight

The sheer size of the brain and its bony case mean that weight-saving must be a priority. Is this why our faces and teeth are so puny ? Put your thumb against your top teeth and your forefinger against your eyebrow. Look at the gap - that's the size of your face, about 50% of the length of your braincase, compared to x% for the wolf and y% for the sheep.

A professional assassain will sometimes shoot her victim in the face because the bullet passes easily through these thin bones, striking the hind brain or brain stem behind. Any damage here is inevitably fatal, whereas people sometimes survive damage to the upper parts of the cerebrum.

Not only our facial bones, but also our teeth and jaws are small and unspecialised. Human jaw muscles are thin sheets (which you can feel if you put your fingers on your temples and clench your teeth) - compare them with the muscles which must have filled the spaces on each side of this tiger's head !