The world’s primates face an “extinction crisis” with 60% of species now threatened with extinction, according to research.
A global study, involving more than 30 scientists, assessed the conservation status of more than 500 individual species.
This also revealed that 75% of species have populations that are declining.
The findings are published in the journal Science Advances.
Professor Jo Setchell from Durham University, a member of the team, explained that the main threats were “massive habitat loss” and illegal hunting.
“Forests are destroyed when primate habitat is converted to industrial agriculture, leaving primates with nowhere to live,” she told BBC News.
“And primates are hunted for meat and trade, either as pets or as body parts.”
Other threats – all driven by human behaviour – are forest clearance for livestock and cattle ranching; oil and gas drilling and mining.
“The short answer is that we must reduce human domination of the planet, and learn to share space with other species,” Prof Setchell commented.
The study also cited poverty and civil unrest as a driving force for hunting – in the poorest parts of the world many people are being driven to hunting primates in order to feed themselves.
“We need to focus on the development of these parts of the world and make sure people have an alternative source of protein,” said Prof Serge Wich from Liverpool John Moores University.
He pointed out that the loss of primate species represented the loss of forests that are essential for the future of our own species.
“These forests provide essential services for people,” he told BBC News.
“They help in being carbon stocks to mitigate climate change; they help in providing clean water and providing pollination services for people, so they can grow their crops.”
The researchers also pointed to some personal choices that people could make as consumers, particularly in the west, to avoid contributing to tropical deforestation.
“Simple examples are don’t buy tropical timber, don’t eat palm oil,” said Prof Setchell.
But more broadly, “we need to raise local, regional and global public awareness of the plight of the world’s primates and what this means for ecosystem health, human culture, and ultimately human survival.
“In industrialised nations, we must decrease our demand for resources that we don’t need, and stop confusing wants with needs.”
Dr Christoph Schwitzer, from the International Union for the Conservation of Nature is also director of conservation at Bristol Zoological Society. He told the BBC that it was his “strong belief” that “with a concerted effort by the world’s governments and conservationists, primate declines can be halted and populations stabilised”.
He added that changes in consumer behaviour could help, for example “choosing FSC-certified wood and paper products, and making sure palm oil comes from sustainable sources”.
Dr Schwitzer added: “Protected areas [of habitat] and efficient law enforcement will be key.”