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 the last 70 had any truly effective means of communicating with one another, only the last 6 ever saw a printed word or 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 with the life span of the eight-hundreth person.
R.L. Lesher and G.J. Howick, Assessing Technology Transfer (NASA Report SP-5067) (1966)