President Richard Nixon signed the Endangered Species Act on Dec. 28, 1973.
As first signed, it represented a tall order: the government was to protect every endangered animal and plant in the U.S. It enjoyed broad bipartisan support and an optimistic endorsement from the president.
"Nothing is more priceless and more worthy of preservation than the rich array of animal life with which our country has been blessed," President Nixon said at the time.
The act says that federal agencies have to make sure their actions don't jeopardize a listed species' existence or damage its habitat. It also prohibits the hunting, trade or killing of its protected species.
Over its 50 year lifetime the Endangered Species Act has brought iconic and diverse species, from the bald eagle to the black-footed ferret, back from the brink of extinction.
But its broad mandate has for decades also conflicted with the construction and development priorities of an urbanizing country.
Colorado releases first 5 gray wolves as part of reintroduction plan
Gray wolves are native to Colorado, but they were systematically exterminated and functionally extinct by the 1940s.
In 1975, the snail darter became an example of just how powerful the law could be.
The tiny fish, originally native only to certain waterways in Tennessee, was listed for protection under the act. This obliged federal agencies to stop work on the Tennessee Valley Authority’s nearly finished Tellico Dam — a requirement that the Supreme Court upheld in 1978. Congress eventually had to make the dam exempt from coverage under the ESA so that it could be completed.
And the dueling pressures the ESA faces persist today.
Habitat loss, climate change, pollution and disease are putting millions of species not just in the U.S. but around the world at risk. At the same time, U.S. industry groups and land owners have pushed efforts to weaken the ESA, defund agencies that uphold it and make more room for development.
Support for the ESA has declined dramatically from the bipartisan levels it enjoyed when it was signed.
But it has made a difference for at least some of the species it protects: A 2023 study by the Center for Biological Diversity found that the ESA has prevented the extinction of roughly 291 species in the U.S.
