Our fellow primates are in trouble.
In a study of unprecedented scope, a team of 31 primatologists has analyzed every known species of primate to judge how they are faring. The news for man’s closest animal relatives is not good.
Three-quarters of primate species are in decline, the researchers found, and about 60 percent are now threatened with extinction. From gorillas to gibbons, primates are in significantly worse shape now than in recent decades because of the devastation from agriculture, hunting and mining.
“I think we’re going to get quite a number of extinctions within next 50 years if things go on the way they are,” said Anthony B. Rylands, a senior research scientist at Conservation International and a co-author of the new study, which was published in Science Advances.
“It’s a landmark paper,” said Anne D. Yoder, the director of the Duke Lemur Center, who was not involved in the study. “It’s alarming without being alarmist.”
Just last week, a team of researchers described a new species of gibbon in China. Dr. Rylands said he knows of at least seven new primate species to be announced this year.
Scientists are finding so many new primate species in part because the destruction of forests is making it easier to reach populations that were once remote.
“There is a certain rush of people in a panic, realizing that if they don’t find and describe them, they will be lost without us ever knowing them,” said Dr. Rylands.
Another reason for the burst of discovery is that scientists have started investigating the DNA of primates, finding that some populations had unique mutations..
“There are distinct species that have been around for millions of years, even though they look to our eyes very similar,” said Dr. Yoder. Unfortunately, she noted, new species revealed by DNA often turn out to exist in perilously low numbers.
The new research was not all bad news for primates.
“Some species are doing O.K.,” said Katherine C. MacKinnon, an anthropologist at Saint Louis University and a co-author of the study. “The ones that are doing O.K. are the ones that aren’t super-specialists, the ones that are most flexible.”
But most species are not so flexible. Every species of ape (including gorillas, chimpanzees, bonobos, orangutans and 19 species of gibbons) is threatened, while 87 percent of lemur species are. Other species that are critically endangered include the brown-headed spider monkey of Ecuador, the Niger Delta red colobus, and the crested macaque, an Indonesian species famous for having taken a selfie with a photographer’s camera.
“It’s worse than we thought 10 years ago,” Dr. MacKinnon said.
She and her colleagues identified a number of human activities pushing primates to the edge, such as hunting. In West Africa, for example, there is a strong demand in local markets for primate meat.
“The forests are still standing, but they’ve shot everything out of it,” said Dr. Rylands.
The incentives to kill primates are not only local, though. A lot of primate meat is making its way to China, along with body parts falsely believed to have healing powers.
“They’ll import enormous amounts from around Southeast Asia,” said Dr. Rylands. “They’re a driving force through the whole region.”
Primates are also threatened by the wholesale destruction of forests to make way for agriculture. In the Amazon, the jungle is being converted to cattle ranches and soybean fields, while in Madagascar, rice paddies are taking the place of lemur forests.
Western countries are also helping push primates toward extinction. Palm oil can be found in everything from doughnuts to lipstick to biodiesel fuel. New palm oil plantations are completely replacing forests in Southeast Asia — one of the most primate-diverse parts of the world.
Even cellphones can add to the risks. In central Africa, miners go into rain forests to dig for an ore called coltan that ends up in phone circuits. Those miners hunt for their meals. “They live on primates,” said Dr. Rylands.
Humans have already driven some primate species extinct, but it’s hard to say exactly how many. Madagascar was once home to giant lemurs that could weigh as much as 350 pounds.
While Western scientists never laid eyes on these remarkable creatures, the fossil record shows that 17 lemur species became extinct after humans arrived there 2,000 years ago.
More recently, a monkey called Miss Waldron’s red colobus has disappeared from its range in West Africa. It has not been spotted for over 25 years and is believed to be extinct. In China, a subspecies called the white-handed gibbon may have gone extinct as well.
Some of the most endangered primate species are down to just a few dozen survivors. Their prospects are grim, because many of them live in parts of the world where human populations are projected to grow the fastest.
In Madagascar, for example, humans may have to move deeper into lemur habitats for new farmland. “It’s a pressure cooker, and there’s no way to relieve the pressure,” said Dr. Yoder.
The authors of the new study offer a number of reasons it is worth trying to halt the crisis.
Recent research has shown that primates are extremely important to the ecosystems in which they live. As they feed on leaves and fruit, for example, they move pollen between trees. They pass seeds in their droppings, allowing plants to spread across a healthy range.
“People used to think of primates as icing on the cake, as not being vital for ecosystems,” said Dr. MacKinnon. “But now we know they are.”
Primates have also been invaluable for understanding ourselves.
The first primates evolved roughly 80 million years ago, and then split into the living lineages over millions of years. By comparing our biology to those of other primates, we have learned about the evolution of our brains, our vision and our vulnerability to diseases.
If those species become extinct, we will lose the opportunity to learn more.
While the prospects are dire, Dr. Rylands said there were concrete steps that can be taken to help primates. “You have to stop hunting them and give them a place to live,” he said.
That is easier said than done, he acknowledged, since the local communities where primates live are often struggling to feed their families. In some cases, it may be possible to take the pressure off primates by building fish farms as an alternate source of protein.
In other cases, communities may be able to make more money over the long term from tourist operations in intact forests than from slash-and-burn agriculture.
Dr. Rylands pointed to the golden lion tamarin as an example of how a primate species can be saved. It once lived in huge numbers in the Atlantic coastal forests of Brazil. After the forests were nearly wiped out to make way for sugar plantations and other forms of agriculture, the species nearly vanished.
In 1983, the U.S. National Zoo led an international effort to bring them back. Monkeys were bred in captivity, forests were conserved and hunting was banned.
Today, the species has a small but stable population of some 3,500 individuals in the wild.