During most of human history, people have been guided in their actions by traditional customs and beliefs, not by consideration of short-term self interest. At present there is a growing contempt for such blind faith as people believe they are more rational. But old customs, which evolved over long periods, often (although not always) had deeper reasons behind them, even if these reasons were not understood by most of the people adhering to such customs. For example, the prohibition by certain religions against the consumption of pork makes sense when it is realized that pork is a frequent transmitter of parasitic diseases. And why did putting a horse in the field where cows were grazing inhibit the development of foot-and-mouth disease ? Traditional modes of behaviour often served the function of letting people live in peace with nature and with one another. As such traditions lose their power over people's ways of conducting themselves and are evaluated critically, they must be replaced by a new awareness of necessities, based on a more scientific understanding of the world which will lead people to behave in ways consistent with long-term survival. Otherwise loss of reverence for nature and for life may lead to disaster.