The tarsiers of the Philippines are the smallest primates on the planet, at about five inches tall. They tend to keep their hind legs, which are twice as long as their bodies, folded up frog-style, except when leaping on their insect prey. And a tarsier eyeball, at just over half an inch wide, is as large as a tarsier brain.

But the weirdness doesn’t stop there. No, it most certainly does not.

Scientists had previously remarked that tarsiers were unusually quiet. And they also seemed to yawn quite a lot. Aww, cute, right? Sweepy wittle pwimates! But then, some scientists studying tarsiers made a startling discovery. Zoe Corbyn at New Scientist sums it up well: “Placing 35 wild animals in front of an ultrasound detector revealed that what [the scientists] assumed to be yawns were high-pitched screams beyond the range of human hearing.”

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The number of traits chalked up as “distinctly human” seem to dwindle each year. And now, we can’t even say that we’re uniquely aware of the limits of our knowledge: It seems that some monkeys understand uncertainty too.

A team of researchers taught macaques how to maneuver a joystick to indicate whether the pixel density on a screen was sparse or dense. Given a pixel scenario, the monkeys would maneuver a joystick to a letter S (for sparse) or D (for dense). They were given a treat when they selected the correct answer, but when they were wrong, the game paused for a couple seconds. A third possible answer, though, allowed the monkeys to select a question mark, and thereby forgo the pause (and potentially get more treats).

And as John David Smith, a researcher at SUNY Buffalo, and Michael Beran, a researcher at Georgia State University, announced at the AAAS meeting this weekend, the macaques selected the question mark just as humans do when they encounter a mind-stumping question. As Smith told the BBC, “Monkeys apparently appreciate when they are likely to make an error…. They seem to know when they don’t know.”

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For more top lists check out DISCOVER’s top 100 stories of the year and the 2010 top ten most-read stories from 80beats.

In some monkey species, monkey moms use snuggle time with their babies as a commodity. Mothers will “sell” time with their children to other females in their colony for the price of several minutes of grooming. As Science News puts it, they have a “do my hair before you touch my baby” rule.

The research team who made this discovery, which was described in the journal Animal Behaviour, studied vervet monkeys and sooty mangabeys in the Ivory Coast’s Tai National Park. Newborn infants draw crowds of female monkeys who want to touch, hold, and make lip-smacking noises at the babies. Touching of the baby can be had for a price of a few minutes spent grooming its mother, though it’s not really known why female monkeys are so drawn to the young of others.

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The locals living in a remote Burmese forest gave wildlife biologists very clear instructions on how to find a rare species of monkey: Just go out on a rainy day, and listen for sneezes in the treetops. The snub-nosed monkey has nostrils that point up, they said, and it sneezes when rainwater drips into its nose.

Even with these amazingly great directions, the biologists failed to photograph a live specimen of the Burmese snub-nosed monkey–the image at right is a digital reconstruction of what the monkey probably looks like. Still, their examination of skins and skulls in the villagers’ possession provided enough evidence to declare that the monkey was a new species that had never before been described in the scientific literature. BBC reports:

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Want to attract a good mate and ward off unknown relations? Secrete a smelly substance from that gland on your chest and rub it all over. At least that’s what a mandrill might do: A recent study suggests that the baboon-like primates may use their smelly secretions to distinguish compatible mates from family.

After taking swabs from mandrill sternal glands, researchers genotyped each sample to determine the monkey’s major histocompatibility complex (MHC)–a unique genetic signature related to the animal’s immune system. They also, using a sorting technique called gas chromatography–mass spectrometry, determined each secretion’s chemical makeup, and thus its stink bouquet.

As the study’s leader Leslie Knapp of Cambridge University told the BBC, more “genetically diverse” mandrills, i.e. unrelated, have different MHCs and chemically-speaking different scents:

“[I]t seems that the odour is something that tells us some really important things about the genes of a mandrill.”

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Chalk up another mark of chimpanzee intelligence–they not only use tools for gathering food, but also to improve their sex lives.

The chimps don’t have to duck into a sex shop to gather their erotic implements—the tools they use literally grow on trees. Researchers have documented chimps in a Tanzanian colony using brittle leaves in their mating rituals.

In a botanical bit of foreplay, the male chimps grab dry leaves and break them apart with their hands or mouths, creating a distinctive raspy sound that signals their sexual readiness. Think of it as the chimp equivalent of putting “Let’s Get It On” on the stereo.

As researcher William McGrew explains (slightly graphically) to The New York Times:

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Fool me with monkeys once, shame on you. Fool me twice… well, Puerto Ricans won’t get fooled again.

Some people on the island commonwealth are up in arms over the proposal by a company called Bioculture Ltd. to make Puerto Rico a major supplier of primates to researchers in the United States. Beyond the ethical issues connected to animal testing, the AP reports, Puerto Ricans have “a bad history with research monkeys”:

The U.S. territory has long struggled to control hundreds of patas monkeys, descendants of primates that escaped in recent decades from research projects and now thrive in the lush tropical environment.

No labs want the patas monkeys because they’re no longer right for research, and many are diseased. There isn’t much demand from zoos, either. So rangers from the island’s Department of Natural Resources trap and kill them.

Bioculture counters that its proposed facility in the mountainous region of Guayama would bring 50 jobs and other economic benefits, like buying fruit from local farms to feed the African monkeys, to a place currently reeling from 16 percent unemployment. Bioculture executive Moses Mark Bushmitz tried to reassure people from the Guyama neighborhood of Carmen, which is near the proposed facility, that their homes would be no more run over with research primates than homes in Cambridge, Mass.:

“You have monkeys in MIT, you have monkeys in Harvard,” Bushmitz said. “So why isn’t it an issue if the monkey will escape in Harvard, but it is an issue if a monkey will escape in Carmen?”

To be fair, though, there isn’t a history of monkeys that “run though backyards, stop traffic and destroy crops” in Harvard Yard.

Related Content:
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80beats: NASA’s Plan to Irradiate Monkeys Raises Cruelty Concerns

Image: flickr /Mr. Theklan

The muriqui have a reputation as being one of the gentlest, most social of the primates—so much so that they’ve been dubbed the “hippy monkey.”But even the sweetest of animals will turn murderous when deprived of basic needs—in this case, sex. New Scientist reports that a gang of six muriqui was spotted pulling a “Lord of the Flies” on an older male:

The victim, an old male, died an hour after receiving savage bites to his face, body and genitals. The observations, published this week in the American Journal of Primatology, show how lifestyles may dramatically alter the behaviour of a species.

So why would these peaceful creatures, close relatives of spider monkeys found only in the Atlantic forests of Brazil, turn to such savagery? NS explains:

The muriqui’s peaceful reputation stems mainly from northern populations that feed on abundant leaves, and where males patiently queue to mate with females.

But in the southern population where the attack took place, fruit is more widely available than in the north, and this may provide a clue to the assault, says Mauricio Talebi of the Federal University of São Paulo-Diadema, Brazil, who led the research.

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Just as humans and gorillas share a common evolutionary ancestry, the pubic lice that infuriate some members of the two species are also related. Pubic lice–known to scientists as Pthirus pubis and to most other people as “crabs”–are thought to have evolved from Pthirus gorillae, the structurally similar species that infests gorillas. Genetic analysis by David Reed at the University of Florida indicates that the lice lineages split about 3.3 million years ago, whereas it is believed that humans diverged from gorillas at least 7 million years ago. This suggests that “early humans somehow caught pubic lice from their gorilla cousins.”

But apparently the lousy parasite didn’t make the jump because humans and gorillas tried to reunite their bloodlines; no, University College London biologist Robin Weiss suspects that humans picked up crabs by hunting gorillas. Because a predator can easily pick up parasites from its prey, the lice could have jumped to early humans while they butchered gorillas for bushmeat. Some researchers say that HIV made its more recent jump from chimpanzees to humans the same way.

Image: Flickr / mrflip