Fun story from Dinotopia illustrator James Gurney:
When National Geographic asked me to paint a small illustration of a Neanderthal father telling a story to his son, the art director emphasized that he should look recognizable, "like a guy who stepped off the subway." Only the heavy brow ridge should give him away.
Where to find a model? I racked my brain for who would fit the part. One guy I knew named Jim would be ideal. But how should I ask him to pose? "Hey, Jim, would you mind posing for a Neanderthal picture I'm doing?" I was afraid he might be insulted.
I managed to ask him, and he cooperated. Later I asked him if he minded being a cave man. "Not at all," he replied with a smile. "My girlfriend says it gives me more sex appeal."
A terrific illustration, too! Link