Well, who knows for sure about Cro-Magnon Man, but I am sure there has been variation in the size of mens penises for a very, very, very long time. I am also sure that whenever someone was in a position to see a lot of dicks, either in single gatherings or individually over time, he or she became cognizant of the variation. However, since very large cocks are uncommon, I suspect seeing one for the first time back in the day was quite a revelation. Nowadays, with the advent of modern porn and with more relaxed social mores on the topic, I think many more people are more conscious that some men are well hung and some are not.