Foreword

To start, put yourself in a hypothetical situation: you have an identical twin brother who was secretly transferred to another family when you were less than a year old. His new family was poor, and your family was rich and therefore the environment in which you grew up was much better than his. After 50 years, by chance, you both happen to meet and it turns out that you look quite different from one another and are in different states of health; he is short and is suffering from heart disease, while you are tall, healthy, and are training to run a marathon. So, what was it that made you two so different, in light of the fact that your genetic materials are completely identical?