The world's primates are being threatened by one of their own — us.

In a bleak new study published this week in the journal Science Advances, 31 top primatologists warn that the planet could see a mass extinction of nonhuman primates as a consequence of human activities. Some 60 percent of species are in danger of becoming extinct, the researchers write, and a full 75 percent are in decline. If the effects of habitat loss, hunting and man-made climate change aren't mitigated, they say, our closest animal cousins will start to vanish in the next 25 to 50 years.

“This truly is the 11th hour for many of these creatures,” University of Illinois anthropology professor Paul Garber, who co-led the study, said in a statement.

The study is one of the most comprehensive surveys of the world's 504 nonhuman primate species. It's a big group, ranging from tiny, nocturnal lorises to the gargantuan great apes and spanning most of the planet's tropical and subtropical regions. Researchers are still uncovering new species; just last week, scientists named a new type of gibbon that dwells in southwest China.

The outlook for most populations is grim. Only 200 of those newly named gibbons, Hoolock tianxing, are known to be living in the wild, according to the BBC. Other numbers are far smaller — as of 2014, just 50 of Madagascar's Northern Sportive Lemurs were still around.

Garber and his colleagues catalogued the ongoing threat to primate populations, of which there are many: hunting for bushmeat and body parts to sell on the black market, the illegal trade of primates as pets, the increased instance of anthroponotic illnesses (diseases transferred from humans to animals) and the wide-ranging effects of climate change.

Perhaps the biggest problem is habitat loss from the expansion of cities, industrial agriculture, ranching, logging, oil and gas drilling, mining, dam building and road construction, which are carried out “in needlessly destructive and unsustainable ways,” Garber said. The vast majority of primate species live in just four countries — Brazil, Indonesia, Madagascar and Congo — and in those nations, they are confined to shrinking forest homes.

But the future looks grave not just for primate species but for all creatures in tropical and subtropical forest ecosystems, according to the report. The problems facing primates, Garber and co-author Anthony Rylands argue, mirror the threats to biodiversity at large.

“Many people would say, ‘Oh dear, you know, this species is in trouble and that species is in trouble,’ ” Rylands said in a video released by the American Association for the Advancement of Science, which publishes Science Advances. Rylands is deputy chair of the Species Survival Commission’s Primate Specialist Group, part of the International Union for Conservation of Nature, and a senior research scientist at the Virginia-based Conservation International.

“But few people can see the really big picture, which is that human activities … are resulting in the demise of tropical forests around the world, and this has serious consequences for not just the primates,” Rylands continued. “Loss of these forests affects water supply, affects climate change, affects all sorts of major conservation issues around the world.”

Primates play a significant role in ecosystems, the authors note. They help transfer pollen between the trees they feed in and pass seeds in their droppings, allowing plants to spread. They're also important model organisms, essential to understanding the evolution of our own species. Researchers study primates for insights into human behavior, parenting, conflict, learning and memory, social bonds, language and cognition.

And it's up to humans to protect them, the researchers say. They suggest that protected areas be expanded and sustainable land-sharing programs, which ensure that both people and animals can make use of forests, be improved. Better monitoring programs need to be set up to protect wild animals and prevent illegal trade, and steps should be taken to reduce the impact of human activities on forest ecosystems.

These steps will not be easy, they acknowledge. The most vulnerable primates often live alongside the most vulnerable human communities, where poverty, inequality, poor governance and violent conflict hamper efforts to improve conditions. Hunting bushmeat is often an important source of food and income, as are the farms and industries that threaten primate habitats. “Improving the human condition” is the first step the report's authors list in their recommendations for addressing conservation needs.

“We have one last opportunity to greatly reduce or even eliminate the human threats to primates and their habitats, to guide conservation efforts and to raise worldwide awareness of their predicament,” they conclude. “Primates are critically important to humanity. After all, they are our closest living biological relatives.”

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