Holism and connectivity
The sign graph above  gives our summary of the video in the previous step. Collapsing roofs and an infestation of rats were unintended consequences of the DDT spraying problems. As a result of this and other examples, the use of DDT is banned or severely restricted in most countries. For example:
The U.S. Department of Agriculture, the federal agency with responsibility for regulating pesticides before the formation of the U.S. Environmental Protection Agency in 1970, began regulatory actions in the late 1950s and 1960s to prohibit many of DDT’s uses because of mounting evidence of the pesticide’s declining benefits and environmental and toxicological effects. The publication in 1962 of Rachel Carson’s Silent Spring  stimulated widespread public concern over the dangers of improper pesticide use and the need for better pesticide controls.
Since the 1950s, the intense interconnectedness and holistic nature of ecological systems have become much better understood. Furthermore, the advent of the computer in the 1960s and the fantastic increase in power of information and communication technologies have enabled a new science of complex systems that enables to outcome of policies to be probed in greater depth than was possible fifty years ago. Even so, policies such as encouraging the production of biofuels have the unintended, but not unknown, consequence of contributing to starvation:
In 2010, the USA burned 138 million tons of corn and hundreds of million tons of grain in order to manufacture ethanol and biodiesel. If you have a car that runs on biofuel, you would have to use 352 kilograms of corn in order to fill up a 50-liter tank. A child in Zambia or Mexico – where corn is a basic staple – could live on this amount for a whole year. 
What do you think?
What is your view on unintended consequences? Is it possible for policy makers to avoid unintended consequences? Do you have experience of a policy that had unintended consequences? Should the policy makers have been more cautious? Should they have analysed the outcomes more carefully? Give your views and experiences in the comments below.
 This diagram replaces a previous version in response to a comment made by Patricia Sims in March 2018. Click here for a one-page discussion of the changes made to the previous diagram
 Rachel Carson, Silent Spring, Houghton Mifflin Company ,Boston, 1962
 US Environmental Protection Agency, DDT - A Brief History and Status, 2016.
 Janine Albrecht (interviewer), Jean Ziegler: ‘Biofuels a big cause of famine’, Deutsche Welle, 1/5/2013.