Eight hundred life spans can bridge more than 50,000 years. But of these 800
people, 650 spent their lives in caves or worse; only 70 had any truly
effective means of communicating with one another; only the last 6 ever saw a
printed word or had had any real means of measuring heat or cold; only the
last 4 could measure time with any precision; only the last 2 used an electric
motor; and the vast majority of the items that make up our material world were
developed within the lifespan of the eight-hundreth person.
R. L. Lesher and G. J. Howick

The above was the signature for a friend who was a postdoc at a physics lab I used to work at. I just thought it was a very interesting quote.