I always thought that it was because life was so hard back then. But then my brother, who is a photographer, explained what everyone else has said. They had to stand so still for such a long period of time that they didn't smile. I am surprised that I have rarely seen an old-time picture where someone was photographed with their eyes closed. Which also explains why they have such strange looking expressions in some of the photographs. Can you imagine not blinking for that whole time. Dry eyes, anyone?