CONTENTS 



Preface v 



I. Different Kinds of Evolution 1 



II. The Four Great Historical SjJeculations 7 



THE ENVIRONMENT 7 



USE AND DISUSE 10 



THE UNFOLDING PRINCIPLE 12 



NATURAL SELECTION 14 



III. The Evidence for Organic Evolution 17 



THE EVIDENCE ITIOM COMPARATIVE 



ANATOMY 17 



THE EVIDENCE FROM EMBRYOLOGY 23 



THE EVIDENCE FROM PALEONTOLOGY 32 



THE EVIDENCE FROM GENETICS 35 



IV. The Materials of Evolution 41 



V. MendeVs Two Latvs of Heredity 55 



mendel's first law 57 



mendel's second law 66 



• • 

 Vll 



