Georgina Mace, Who Shaped List of Endangered Species, Dies at 67

She rewrote the global Red List, which describes which species are in trouble, and warned that the world must restore its ecological balance or pay a steep price.

When Georgina Mace was thinking about taking on a new challenge — to improve a system for determining which species around the world were at risk of going extinct — “my boss at the time advised me not to touch it,” she said in 2016, because the task “could end up being a lot of work for no purpose at all.”

Luckily for the planet, she disagreed.

Dr. Mace, one of the world’s most prominent conservation biologists, went on to provide a firm scientific foundation for a list of endangered species that had for many years been compiled by the International Union for Conservation of Nature. Called the Red List, it helps governments and environmental groups decide how to focus their efforts.

The Red List was initially “a haphazard affair” when it was created in 1964, said Simon Stuart, director of strategic conservation for Synchronicity Earth, an environmental charity, and a former official of the International Union for Conservation of Nature. There were no solid criteria for determining which animals should or should not be listed. Rather, “politics and personalities played a big role in decisions,” he said in a phone interview, and the list tended toward so-called “charismatic” species, like the great apes.

In the early 1990s, Dr. Mace, then working for the Zoological Society of London, began the long process of developing the criteria for a more scientifically disciplined list. The challenge: to develop a practical method rigorous enough to be convincing but simple enough to be rapidly applicable to thousands of species.

“Her genius was to find that balance,” said H. Reşit Akçakaya, a professor in the department of ecology and evolution at Stony Brook University on Long Island.

Dr. Mace died on Sept. 19 in hospice care in Oxford, England. She was 67. Her death, which was not widely reported in the mainstream press, was caused by breast cancer, her brother Dr. Peter Mace said.

Humans are causing species of animals and plants to decline at an accelerating rate, with as many as one million now at risk of extinction — a prospect that threatens to disrupt ecosystems that people around the world depend on for survival. The causes are numerous and complex; they include deforestation and other forms of habitat disruption, hunting and overfishing, transport of invasive species, and climate change.

In giving the Red List its more scientific underpinnings, Dr. Mace used a methodology based on the science of population dynamics and on evidence of species decline. Extinction risk, it turned out, could be measured from a small number of ecological characteristics, including a species’ evolutionary history and its rate of population growth or loss.

Her system has proved not only remarkably effective and durable but also flexible enough to incorporate climate change as an extinction threat. The list has grown to include more than 120,000 species of animals, plants and fungi; some 32,000 are currently listed as endangered.

Dr. Mace’s methods were considered radical at first. Dr. Stuart recalled that in the mid-1990s, representatives of government agencies regulating fisheries argued that it was wrong to list commercially viable fish like bluefin tuna and North Atlantic cod as endangered when they were seemingly still plentiful. In his view they were at risk because they were being overfished.

“I was feeling intimidated,” Dr. Stuart said. “But Georgina remained calm and answered all points with accuracy and self assurance, and disarmed her opponents.” The listing stayed.

In a 2016 interview with the BBC, Dr. Mace said, “People still criticize the criteria, but everybody accepts that there’s a universal system.”

Nathalie Pettorelli, a senior scientist with the Zoological Society of London, said of Dr. Mace, “She was never the one that shouted, but she was always the one that would be listened to.”

Beneath that quiet demeanor was a crackling wit. Dr. Stuart recalled a scientific meeting when he asked Dr. Mace politely — perhaps too politely — to take on more duties.

“Simon, you slimy toad,” she responded, smiling. He recalled the moment as “one of my greatest honors,” adding, “and, of course, she went on and did it.”

Georgina Mary Mace was born in the Lewisham borough of South London on July 12, 1953, to Dr. Bill Mace, a rheumatologist, and Josephine (Bruce) Mace, a nurse and medical illustrator.

She received her undergraduate degree in zoology from the University of Liverpool in 1975 and her Ph.D. in biology from the University of Sussex in 1979. After completing postdoctoral work at the Smithsonian Institution in Washington, she returned to Britain went to work for the Zoological Society of London, eventually rising to director of science. She held a position at Imperial College London from 2006 to 2012, when she joined University College London.

A fellow of the Royal Society, she was made a dame of the British Empire in 2016.

Dr. Mace married Rod Evans, who survives her, in 1985. In addition to him and her brother, she is survived by three children, Ben, Emma and Kate; one grandchild; and another brother, Edward.

Dr. Mace championed restoration of biological diversity and was a major contributor to a project called the Millennium Ecosystem Assessment, which laid out the value of a healthy natural planet for the world’s people and its economies.

In a tribute on the website of the British Ecological Society, Professors Jon Bridle and Kate Jones of the Center for Biodiversity & Environment Research at University College London wrote that Dr. Mace’s work had “helped to reveal the ecological emergency that we face, and that we have less than a decade to prevent.”

“Perhaps her most remarkable achievement,” they added, “was the way she could calmly convince an audience of this fact, while expressing an unwavering optimism that we still have time to forge a more creative interaction with the rest of nature, one that benefits more than a wealthy minority, and one that can last more than just a few more decades.”

Dr. Mace continued to work even after she learned she had cancer. “She never mentioned her illness to others unless she absolutely had to,” her brother Peter, a physician, said. “She didn’t want to be categorized by it. She wanted to get on with her life, to get on with her job, which she enjoyed hugely.”

To her, he said, the disease “was an irrelevance, a nuisance.”

Shortly before her death, the journal Nature published an article co-written by Dr. Mace suggesting that “bending the curve” of species loss could still be addressed, and nature’s balance restored, through an ambitious international effort.

Dr. Mace acknowledged in a 2009 interview with The Guardian that “it is hard to be optimistic — we are not yet even embarking on doing the right things for the planet.” Still, she added, “All the evidence to date is that when societies put their mind to solving a problem, they can generally do it.”