1973: The Endangered Species Act is signed into law by President Nixon.

The act came into being as Americans grew increasingly aware of the damage being done to the environment and the threat posed to specific animal and plant species by rampant economic growth.

Declaring existing conservation policies inadequate, Nixon tasked Congress with devising new legislation aimed specifically at protecting species and their ecosystems threatened by economic encroachment. The result was the Endangered Species Act.

The wide-ranging act forbids any government agency from funding or participating in any action that may “jeopardize the continued existence” of any endangered or threatened species. There are also provisions for private citizens to take legal action against the government to make sure the act is enforced.

Individual plant and animal species are added to a protection list and categorized as either “endangered” or “threatened” based on a number of factors, including population figures and the condition of the habitat. If conditions improve significantly, they can be downgraded from “endangered” to “threatened,” or even removed from the lists. Currently, there are nearly 2,000 plant and animal species on the lists.

Two agencies, the U.S. Fish and Wildlife Service and the National Oceanic and Atmospheric Administration, are responsible for administering the act.

There have been a number of well-publicized legal challenges as a result of the Endangered Species Act, resulting in the delay of some projects and the complete scrapping of others.

The ESA suffered considerably under the George W. Bush administration, while the Barack Obama administration has received higher marks.