Written By: Eliza Berman

In 2015 the Oregon chub was removed from the Federal List of Endangered and Threatened Animals, becoming the first fish ever to shed its endangered status. When it was placed on the list in 1993, there were fewer than 1,000 of the minnow species left. At the time of removal there were more than 140,000.

In the years since the first official list of threatened and endangered species was published in 1967, 28 species have been recovered, 10 have become (or were discovered to already be) extinct, and more than 2,000 species have joined the original 78.

Though the notion of extinction entered public awareness at the turn of the 20th century and the federal government began taking steps to protect certain species then, it wasn’t until the 1960s that environmental activism pressured the government to be more proactive in identifying and taking measures to protect threatened species. The first significant piece of legislation, the Endangered Species Protection Act, was passed in 1966, followed by an amendment in 1969 and a reworking in the 1973 Endangered Species Act.

Liz Ronk edited this gallery for LIFE.com. Follow her on Twitter at @LizabethRonk.

Henry, a 12-pound orangutan at the St. Louis zoo, wakes from a nap in his incubator.

Henry, a 12-pound orangutan at the St. Louis zoo, woke from a nap in his incubator.

Nina Leen The LIFE Picture Collection/Getty Images

Orangutan, 1964

Orangutan, 1964.

Nina Leen The LIFE Picture Collection/Getty Images

Oryx, 1964

Oryx, 1964.

Nina Leen The LIFE Picture Collection/Getty Images

With her floppy ears cocked, the newest addition to San Diego zoo's okapi herd of five stands protectively near her mother.

Okapi, San Diego zoo, 1964.

Nina Leen The LIFE Picture Collection/Getty Images

Ocelot, 1964

Ocelot, 1964.

Nina Leen The LIFE Picture Collection/Getty Images

Hilda, the 15-year-old grande dame of Detroit's bears, cradles her latest set of twins, her fourth pair.

Hilda, the 15-year-old grande dame of the Detroit zoo’s bears, cradled her latest set of twins, her fourth pair.

Nina Leen The LIFE Picture Collection/Getty Images

Growling hungrily, polar bears at Detroit's zoo wait for their next meal while one impatient female gets up on her hind legs for a better look.

Growling hungrily, polar bears at Detroit’s zoo waited for their next meal while one impatient female rose on her hind legs for a better look.

Nina Leen The LIFE Picture Collection/Getty Images

Przewalski's wild horses, believed extinct in their habitat on the Mongolian steppes, are bred at the Catskill Game Farm, a private zoo in Catskill, N.Y. There are 120 of these horses in the U.S. and Europe, and in 20 years breeders hope to release some back into the wild.

Przewalski’s wild horses, believed extinct in their habitat on the Mongolian steppes, were being bred at the Catskill Game Farm, a private zoo in Catskill, N.Y.

Nina Leen The LIFE Picture Collection/Getty Images

Tusk to tusk, two white rhinos eye each other at the Oklahoma zoo. The largest of all rhinos, they came from Zululand in South Africa where only 300 survive. No white rhino has yet been born in the U.S. through several zoos have pairs today and hope to mate them.

Tusk to tusk, two white rhinos eyed each other at the Oklahoma zoo. The largest of all rhinos, they came from Zululand in South Africa where only 300 survived.

Nina Leen The LIFE Picture Collection/Getty Images

Whooping Crane, 1964

Whooping Crane, 1964.

Nina Leen The LIFE Picture Collection/Getty Images

The cheetah, which is native to Africa and India, grows lethargic in captivity and does not mate. At the Oklahoma zoo the docile male (above) is being given plenty of exercise in the hopes of solving the problem. In fact the zoo believes the female (rear) may be pregnant.

Cheetahs at a zoo in Oklahoma, 1964.

Nina Leen The LIFE Picture Collection/Getty Images

Cheetahs, 1964

Cheetahs at an Oklahoma zoo, 1964.

Nina Leen The LIFE Picture Collection/Getty Images

Koala, 1964

Koala, 1964.

Nina Leen The LIFE Picture Collection/Getty Images

Two young tortoises crawl by 500-pound, century-old adult at the San Diego zoo. These huge tortoises, one of the most ancient of animals, are facing extinction in their native homes. San Diego, the zoo that has most successfully bred them, is raising 18 young ones and has 92 eggs in their incubators waiting to hatch.

Two young tortoises crawled by a 500-pound, century-old adult at the San Diego zoo.

Nina Leen The LIFE Picture Collection/Getty Images

The only pair of captive bongos in the world butt each other at the Cleveland zoo. Though the 18-month-old male (left) is not yet fully mature, he already as a sparing interest in the female. His horns eventually will be 36 inches long. Bongos are so elusive in the deep Central African forests that no one knows how many are left.

Bongos, a kind of antelope, at a zoo in Cleveland, 1964. At the time they were the only pair in captivity.

Nina Leen The LIFE Picture Collection/Getty Images

Pygmy Hippos, 1964

Pygmy Hippos, 1964.

Nina Leen The LIFE Picture Collection/Getty Images

Zata, one of three pygmy hippos born this year at Washington's zoo, lies at ease in his daily bath. He is not yet allowed in the zoo's small pool he might b stepped on and drowned. These hippos which grow only two feet in height, come from the west coast of Africa.

Pygmy hppos at the Washington zoo, 1964.

Nina Leen The LIFE Picture Collection/Getty Images

Tapir, 1964

Tapir, 1964.

Nina Leen The LIFE Picture Collection/Getty Images

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