[1]
A. INTRODUCTION

LECTURE I

DESCENT: THEORIES OF EVOLUTION
AND METHODS OF INVESTIGATION

Newton convinced his contemporaries that natural laws rule the whole
universe. Lyell showed, by his principle of slow and gradual evolution,
that natural laws have reigned since the beginning of time. To Darwin we
owe the almost universal acceptance of the theory of descent.

This doctrine is one of the most noted landmarks in the advance of
science. It teaches the validity of natural laws of life in its broadest
sense, and crowns the philosophy founded by Newton and Lyell.

Lamarck proposed the hypothesis of a common origin of all living beings
and this ingenious and thoroughly philosophical conception was warmly
welcomed by his partisans, but was not widely accepted owing to lack of
supporting evidence. To Darwin was reserved the task of [2] bringing the
theory of common descent to its present high rank in scientific and
social philosophy.

Two main features in his work have contributed to this early and
unexpected victory. One of them is the almost unlimited amount of
comparative evidence, the other is his demonstration of the possibility
of a physiological explanation of the process of descent itself.