And with it Darwin was a great constructive thinker.

He had the intellectual strength which put the judgment of his time to the strain--everybody's but his own.

This is seen in the fact that Darwin was not the first to speculate in the line of his great discovery, nor to reach formulas; but with the others guessing took the place of induction.

The formula was an uncriticised thought.

The unwillingness of society to embrace the hypothesis was justified by the same lack of evidence which prevented the thinkers themselves from giving it proof.