The Cresswell Horsehead and where does our need to make marks come from?

A week Saturday I'd gone to Chichester without a sketchbook. On the train home I drew these on the back of a brown paper bag.

When I've imagined being imprisoned somewhere - like you do :-) - as well as the obvious fears - one thing that would concern me would be not having access to paper and pens.
I wish I knew more and understood more in an anthropological and psychological way about where this need to make marks comes from and why we as humans have it?

On the BBC documentary the "History of Ancient Britain" a couple of weeks ago they showed a beautiful drawing/engraving done 13,000 years ago of a horse's head scratched into a horse's bone. Here is a clip about the Cresswell Horsehead.

When I'm responding to a commission I'm conscious of and considering an end result. But there is something about the sometimes sudden need to draw that is so immediate and the act of making the marks is the total driving force. I feel a much closer connection to the Cresswell Horsehead artist than to all the more recent art historical periods in between him/her and me.

I see the British Museum are planning an exhibition "Creative Beginnings: European art in the Ice Age" from October 27 – February 2012.