The evident concern of Pope Paul VI for the sufferings of mankind, his tireless labours for peace, and his willingness to adopt new initiatives have won him admiration and a respectful hearing far beyond the bounds of the Christian communion. The recent encyclical Humanae Vitae has attracted the attention of many scientists, partly because it is relevant to the population problem and partly because it contains a section specifically addressed to them. Many scientific periodicals concerned with science and human affairs have therefore devoted leading editorials to the encyclical, and many other scientists have commented on it in articles and letters.

Scientists are well aware that the population problem has arisen largely as a result of their work. Advances in medical science have decreased infant mortality, eliminated many killer diseases and increased the average life span, so that populations hitherto static or increasing slowly have begun to increase rapidly, thus outrunning available food supplies and leading to widespread poverty and malnutrition. This is an agonizing situation that cannot be ignored and indeed all those who struggle to solve it are following the command of Christ to feed the hungry, give drink to the thirsty and clothe the naked. Familiar with the properties of the exponential function, scientists know that the only way to solve the problem, and to avert catastrophic famines in the next decades, is to find some way of regulating births. To be effective, the method chosen must be usable by poor, simple and illiterate people.