Earth is a primate planet, thanks primarily to the 7.3 billion humans who inhabit and reshape its surface. But behind this conspicuous sea of people, the story of Earth's roughly 700 other primate species and subspecies is a lot less triumphant.

More than half of those primates are now in serious danger of becoming extinct, warns a new report by 63 of the world's top primatologists and conservationists. Our closest living relatives are being wiped out by large-scale habitat destruction — especially from the burning and clearing of tropical forests — as well as by hunting for food and for the illegal wildlife trade.

That's according to the latest list of Earth's 25 most endangered primates, which is updated every two years by scientists from the International Union for the Conservation of Nature (IUCN), the Bristol Zoological Society (BZS), the International Primatological Society (IPS) and Conservation International (CI).

"This research highlights the extent of the danger facing many of the world's primates," says BZS conservation director Christoph Schwitzer in a statement about the new report. "We hope it will focus people's attention on these lesser known primate species, some of which most people will probably have never heard of."

The list includes a mix of primates long known to be in existential danger, like Sumatran orangutans and eastern lowland gorillas, along with relative newcomers like the Philippine tarsier and the Lavasoa Mountains dwarf lemur from Madagascar, which was only identified as a distinct species two years ago.

"The purpose of our Top 25 list is to highlight those primates most at risk, to attract the attention of the public, to stimulate national governments to do more, and especially to find the resources to implement desperately needed conservation measures," says Russell Mittermeier, chair of the IUCN Species Survival Commission Primate Specialist Group and executive vice chair of Conservation International.

And on top of primates' inherent scientific value, Mittermeier adds, "there is increasing evidence that certain species may play a key role in dispersing the seeds of tropical forest tree species that have a critically important role in mitigating climate change." So, even if we ignore all the other reasons why preserving primates is a good idea, self-interest at least should compel us to save them.

First, though, we should get to know our distant cousins a little better. In no particular order, here's a who's-who of the 25 most endangered primates on the planet:

Red-ruffed lemur (Varecia rubra)

red ruffed lemurThe red-ruffed lemur's reliance on tall, primary forest has become a liability. (Photo: Jean Verhaegen/Getty Images)

  • Status: Critically Endangered
  • Range: Forests of the Masoala Peninsula in northeastern Madagascar
  • Population: Unknown; thought to be in sharp decline due to habitat loss, with its total population shrinking by an estimated 80 percent in 24 years

Rondo dwarf galago (Galagoides rondoensis)

  • Status: Critically Endangered
  • Range: Seven isolated forest patches in Tanzania
  • Population: Unknown; remaining habitat is just 100 square km (40 square miles)

Philippine tarsier (Tarsius syrichta)

Philippine tarsierThe Philippine tarsier is at risk from habitat loss and the pet trade. (Photo: Jasper Greek Golangco/Wikimedia Commons)

  • Status: Near Threatened
  • Range: Mindanao island group, the Philippines
  • Population: Locally common and widespread, according to IUCN, but decreasing rapidly as it's "heavily harvested as food and especially for the pet trade"

Javan slow loris (Nycticebus javanicus)

  • Status: Critically Endangered
  • Range: Three provinces in Indonesia
  • Population: Unknown; severely fragmented and believed to be decreasing

Pig-tailed langur (Simias concolor)

  • Status: Critically Endangered
  • Range: Mentawai Archipelago, Indonesia
  • Population: 3,300 and decreasing, largely due to illegal hunting — even in protected areas such as Siberut National Park, a UNESCO Biosphere Reserve

Hainan gibbon (Nomascus hainanus)

Hainan gibbonThe Hainan gibbon is considered Earth's rarest ape, with just 28 living in a single nature preserve. (Photo: Jessica Bryant/ZSL)

Cat Ba langur, aka golden headed langur (Trachypithecus poliocephalus)

  • Status: Critically Endangered
  • Range: Exists only on Cat Ba Island, off the northeastern coast of Vietnam
  • Population: 60, although recent conservation efforts have slowed decline

Delacour's langur (Trachypithecus delacouri)

  • Status: Critically Endangered
  • Range: Highly restricted area of north-central Vietnam
  • Population: 234 to 275, fragmented into 19 isolated subpopulations

Eastern lowland gorilla, aka Grauer's gorilla (Gorilla beringei graueri)

eastern lowland gorillaThe eastern lowland gorilla is Earth's largest living primate, but it's also in danger of extinction. (Photo: Shutterstock)

  • Status: Endangered (upgrade to Critically Endangered expected in 2016)
  • Range: Rain forests in eastern Democratic Republic of the Congo
  • Population: 2,000 to 10,000, down from 17,000 in mid-1990s

Kashmir grey langur (Semnopithecus ajax)

  • Status: Endangered
  • Range: Chamba Valley, northwestern India
  • Population: Unknown; estimated to be fewer than 500 individuals

San Martín titi monkey (Callicebus oenanthe)

  • Status: Critically Endangered
  • Range: San Martín region, Peru
  • Population: Unknown; thought to have declined by at least 80 percent since 1985 due to the region's high rate of deforestation

Tonkin snub-nosed monkey (Rhinopithecus avunculus)

Tonkin snub-nosed monkeyOnly five small populations of Tonkin snub-nosed monkey are known to exist. (Photo: Quyet Le/Flickr)

  • Status: Critically Endangered
  • Range: Five small forest patches in far northeastern Vietnam
  • Population: Fewer than 250 and declining, due mainly to hunting

Ka'apor capuchin (Cebus kaapori)

  • Status: Critically Endangered
  • Range: Maranhão and Pará, Brazil (eastern Amazon rain forest)
  • Population: Unknown; only three groups are considered viable over the next 100 years

Ecuadorian brown-headed spider monkey (Ateles fusciceps)

  • Status: Critically Endangered
  • Range: Pacific coast of Ecuador, possibly southern Colombia
  • Population: Unknown; has already become locally extinct in several areas amid heavy deforestation and hunting

Sumatran orangutan (Pongo abelii)

Sumatran orangutanOf the nine existing Sumatran orangutan populations, only seven have long-term viability. (Photo: Shutterstock)

  • Status: Critically Endangered
  • Range: Northern Sumatra, Indonesia
  • Population: 6,600, fragmented among nine habitat units by extensive logging and forest clearing in recent years, largely for palm-oil plantations

Northern brown howler monkey (Alouatta guariba guariba)

  • Status: Critically Endangered
  • Range: Minas Gerais, Brazil
  • Population: Fewer than 250 mature animals living in 10 forest patches

Colombian brown spider monkey (Ateles hybridus)

  • Status: Critically Endangered
  • Range: Northeastern Colombia and western Venezuela, with an isolated population in northeastern Venezuela
  • Population: Unknown; most of its former habitat is now either cattle ranches or palm-oil plantations

Roloway monkey (Cercopithecus diana roloway)

roloway monkeyWest Africa's roloway monkey is near extinction mainly due to bushmeat hunting. (Photo: Sebastien Bozon/Getty Images)

  • Status: Endangered
  • Range: Upper Guinean tropical forests, Ghana and Ivory Coast
  • Population: Unknown; considered to be "on the very verge of extinction," according to the BZS, due to habitat loss and poaching for bushmeat

Preuss' red colobus monkey (Procolobus preussi)

  • Status: Critically Endangered
  • Range: Moist, high-canopy forests of Cameroon and Nigeria
  • Population: Unknown; its disappearance from much of its range since the early 20th century is widely blamed on overhunting and habitat loss

Tana River red colobus monkey (Piliocolobus rufomitratus)

  • Status: Endangered
  • Range: Gallery-forest fragments along 60 km (37 miles) of Kenya's Tana River
  • Population: 1,000 and declining; could "very quickly move into the Critically Endangered category," according to IUCN

Western purple-faced langur (Trachypithecus vetulus nestor)

western purple-faced langurDeforestation is the main reason why the western purple-faced langur is critically endangered. (Photo: Wikimedia Commons)

  • Status: Critically Endangered
  • Range: Forests around Colombo, Sri Lanka's most densely populated region
  • Population: Unknown; 80 percent of its historical range is now urbanized

Lavasoa Mountains dwarf lemur (Cheirogaleus lavasoensis)

  • Status: Undetermined (discovered in 2001; identified as a unique species in 2013)
  • Range: Lavasoa-Ambatotsirongorongo Mountains, southern Madagascar
  • Population: Unknown; forest cover is declining in its already small, isolated and fragmented habitat

Lake Alaotra bamboo lemur (Hapalemur alaotrensis)

Lac Alaotra bamboo lemurThe Lac Alaotra bamboo lemur lives only in papyrus reeds around Lac Alaotra, Madagascar. (Photo: Wikimedia Commons)

  • Status: Critically Endangered
  • Range: Papyrus and reed beds surrounding Lac Alaotra, Madagascar
  • Population: 2,500 to 5,000 and decreasing, due to hunting and habitat loss

Perrier's sifaka (Propithecus perrieri)

  • Status: Critically Endangered
  • Range: Dry deciduous and semi-humid forests of northeastern Madagascar; described as "very restricted" distribution by IUCN
  • Population: 1,700 to 2,600 and decreasing, largely due to conversion of its marsh habitat to rice fields

Northern sportive lemur (Lepilemur septentrionalis)

northern sportive lemurThe entire species of northern sportive lemurs is down to about 50 individuals. (Photo: Shutterstock)

  • Status: Critically Endangered
  • Range: Patches of forest near the villages of Madirobe and Ankarongana in the Sahafary region of northern Madagascar
  • Population: Around 50 and decreasing, mainly due to loss of forest for eucalyptus plantations, firewood and charcoal production

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.