Both groups - the PCBs and organochlorine pesticides, can mimic natural sex hormones.
This reduces male sperm counts and generally "feminises" nature. This has led to a new UN convention dealing with persistent organic products, now called POPs.

Another major issue caused by chlorinated chemicals was found in the 1980s. The hole in the ozone layer was found to be caused by CFCs. Again the impacts from work were felt thousands of miles away - in the stratosphere. These were reactions that nobody had guessed about. The universe was changing quite unpredictably.

Ecological organisation

These developments all put pressure on ecology, the study of how organisms interact with each other and their environment. Ecological principles are becoming the key to our future, possibly more important than the similarly named economics.

The ecosystem consists of two parts; the entire complex of organisms, the biome, and the habitat in which they exist. In a mature ecosystem, all the interacting factors are in approximate equilibrium. As an ecosystem is an open system, there are inputs and outputs that "drive" the internal dynamics of the system.

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