1.
S₁: Man has existed for about a million years.
S₆: What its future effects will be is a matter. of conjecture, but possibly a study of its effects hitherto may make the conjecture a little less hazardous.

P: Science' as a dominant factor in determining the beliefs of educated men, has existed for about 300 years; as a source of economic technique, for about 150 years.
Q: When we consider how recently it has risen to power, we find ourselves forced to believe that we are at the very beginning of its work in transforming human life.
R: In this brief period it has proved itself an incredibly powerful revolutionary force.
S: He has possessed writing for about 6,000 years, agriculture somewhat longer, but perhaps not much longer.