But you may urge that the variation which would take place in a single generation would be, as a rule, too slight to be of any practical value to the animal, and could not be fostered by natural selection until greatly enhanced by some other means.  Let us think a moment.  If ten ordinary men run in a foot-race, the two foremost may lead by several feet.  But if the number of runners be continually increased the finish will be ever closer until finally but an atom more wind or muscle or pluck would make all the difference between winning and losing the prize.

Similarly the million or more young of any species of insect in a given area may be said to run a race of which the prize is life, and the losing of which means literally death.  The competition is inconceivably severe.  How indefinitely slight will be the difference between the poorest of the 2,000 or 20,000 survivors and the best of the more than 900,000 which perish.  The very slightest favorable variation may make all the difference between life and sure death.  And yet these indefinitely slight variations continued and aggregated through ages would foot up an immense total divergence.  The chalk cliffs of England have been built up of microscopic shells.

I have tried to give you very briefly a sketch of the essential points of Mr. Darwin’s theory of evolution.  But you should all read that marvel of patience, industry, clear insight, close reasoning, and grand honesty, the “Origin of Species.”  I have no time to give the arguments in its favor or to attempt to meet the objections which may arise in your minds.  I ask you to believe only this much; that the theory is accepted with practical unanimity by scientific men because it, and it alone, furnishes an explanation for the facts which they discover in their daily work.  And this is the strongest proof of the truth of any accepted theory.

Inasmuch as it is accepted by all scientists and largely by the public, it is certainly worth your while to know whether it has any bearing on the great moral and religious questions which you are considering.  And in these lectures I shall take for granted, what some scientists still doubt, that man also is a product of evolution.  For the weight of evidence in favor of this view is constantly increasing, and seems already to strongly preponderate.  Also I wish in these lectures to grant all that the most ardent evolutionist can possibly claim.  Not that I would lower man’s position, but I have a continually increasing respect for the so-called “lower animals.”

Now if the theory of evolution be true, and really only on this condition, life has had a history; and human history began ages before man’s actual appearance on the globe, just as American history began to be fashioned by Anglo-Saxons, Danes, and Normans before they set foot even in England.  We study history mainly to deduce its laws; and that knowing them we may from the past forecast the future, prepare for its emergencies, and avoid or wisely meet, its dangers.  And we rely on these laws of history because they are the embodiment of ages of human experience.