This is an interesting shot because you can see the difference between 'hard light' and 'soft light'. The tonal changes in the sculpting of the face show subtle and graduated shadows to bring out the features - the effect of soft light. Under the jaw is one very hard line of shadow caused by a hard light from above. See the harsh sharp shadow? The difference between these two light sources is astonishing. They create such different effects. I have written a lot about this on my new website.
This shot was taken at one of my favorite places in the world - the Natural History Museum in London. I spent a lot of time there as a child.