I did a story for the Geographic on Meriwether Lewis and William Clark, and Stephen Ambrose was the writer. He said, "I've got the easiest job in the world. I just have to re-tell the story of the greatest fishing, camping, hunting, canoeing trip of all time. You, Sam, have the hardest job, which is, pretend like nothing has happened in the last 200 years.

[ My time and our common culture] it's what I'm photographing, and I'm very involved with that.

There are a lot of ways to be expressive in life, but I wasn't good at some of them. Music, for instance. I was a distinct failure with the cello. Eventually, my parents sold the cello and bought a vacuum cleaner. The sound in our home improved.

We know that photographs inform people. We also know that photographs move people. The photograph that does both is the one we want to see and make.

I started teaching in '76 and I'd been a photographer at the Geographic for six years. But prior to being at the Geographic I was a teacher. Plus my parents were teachers and my brother and my grandparents. So it was the culture of our family to think about teaching, to talk about teaching, to talk about teachers.

I did it once, and National Geographic recruited me. I did it primarily out of curiosity. A lot of legendary photographers had worked on that campaign. Ernst Haas had done the early photography, and I knew him. There's a lore in photography about that campaign, and I was curious.

Life rarely presents fully finished photographs. An image evolves, often from a single strand of visual interest - a distant horizon, a moment of light, a held expression.