Laetoli

From Wiki:


3.5 Million Year old Hominid Footprints in Tanzania





"A line of hominid fossil footprints, discovered in 1976 by Mary Leakey, is preserved in powdery volcanic ash...he hominid prints were produced by three individuals, one walking in the footprints of the other, making the original tracks difficult to discover. As the tracks lead in the same direction, they might have been produced by a group—but there is nothing else to support the common reconstruction of a nuclear family visiting the waterhole together.


I would suggest that "one walking in the footprints of the other, making the original tracks difficult to discover. " is an imperative part of the birth of Culture, before we could write we needed to walk on paths. 


http://en.wikipedia.org/wiki/Trace_fossil
http://en.wikipedia.org/wiki/Laetoli