The picture shows how men in the study were made to smell tears during experiments. You can see that under the circumstances it is impossible not to smell them, and I doubt that in today's life we can catch the smell from a socially acceptable distance between a man and a woman. All this makes me believe that tears started as a chemical signal but later evolved into a social (visual) signal.
In any case, the study offers an insight into brain's ability to morph a physical phenomena into a social one.
tags: detection, science, social, networking, signal, information, philosophy, biology