2 The changes that have taken place are of considerable importance and varied in nature. In the first place there is the rapid increase in population which has made many fear that world population is going to grow faster than available resources, with the consequence that many families and developing countries would be faced with greater hardships. This can easily induce public authorities to be tempted to take even harsher measures to avert this danger. There is also the fact that not only working and housing conditions but the greater demands made both in the economic and educational field pose a living situation in which it is frequently difficult these days to provide properly for a large family. Also noteworthy is a new understanding of the dignity of woman and her place in society, of the value of conjugal love in marriage and the relationship of conjugal acts to this love. But the most remarkable development of all is to be seen in man's stupendous progress in the domination and rational organization of the forces of nature to the point that he is endeavoring to extend this control over every aspect of his own life—over his body, over his mind and emotions, over his social life, and even over the laws that regulate the transmission of life.
Source: Humanae Vitae (Vatican.va)