|White-headed capuchin (Cebus capucinus)|
The capuchins (pron.: // or //) are New World monkeys of the subfamily Cebinae. Prior to 2011, the subfamily contained only a single genus, Cebus. However, in 2011 it was proposed to split the capuchin monkeys between the gracile capuchins in the genus Cebus and the robust capuchins in the genus Sapajus. The range of capuchin monkeys includes Central America and South America as far south as northern Argentina.
The word capuchin derives from a group of friars named the Order of Friars Minor Capuchin, an offshoot from the Franciscans, who wear brown robes with large hoods covering their heads. When explorers reached the Americas in the 15th century they found small monkeys who resembled these friars and named them capuchins. When the scientists described a specimen (thought to be a Golden-bellied capuchin) they noted that: "his muzzle of a tanned color,... with the lighter color around his eyes that melts into the white at the front, his cheeks..., give him the looks that involuntarily reminds us of the appearance that historically in our country represents ignorance, laziness, and sensuality." The scientific name of the genus, Cebus, on the other hand, comes from the Greek word kêbos, meaning a long-tailed monkey.
In 2011, Jessica Lynch Alfaro et al proposed that the robust capuchins (formerly the C. apella group) be placed in a separate genus, Sapajus, from the gracile capuchins (formerly the C. capucinus group) which retain the Cebus genus. Other primatologists, such as Paul Garber, have begun using this classification.
According to genetic studies led by Lynch Alfaro in 2011, the gracile and robust capuchins diverged approximately 6.2 million years ago. Lynch Alfaro suspects that the divergence was triggered by the creation of the Amazon River, which separated the monkeys in the Amazon north of the Amazon River, which evolved into the gracile capuchins, from those in the Atlantic Forest south of the river, which evolved into the robust capuchins. Gracile capuchins have longer limbs relative to their body size than robust capuchins. Gracile capuchins have rounder skulls, whereas robust capuchins have jaws better adapted for opening hard nuts. Robust capuchins have crests and the males have beards.
- Genus Cebus
- White-fronted capuchin, Cebus albifrons
- White-faced or white-headed capuchin, Cebus capucinus
- Kaapori capuchin, Cebus kaapori
- Wedge-capped capuchin, Cebus olivaceus
- Genus Sapajus
- Black-capped, brown or tufted capuchin, Sapajus apella
- Blond capuchin, Sapajus flavius*
- Black-striped capuchin, Sapajus libidinosus
- Black capuchin, Sapajus nigritus
- Golden-bellied capuchin, Sapajus xanthosternos
* Rediscovered species.
Physical characteristics 
Capuchins are black, brown, buff or whitish, but their exact color and pattern depends on the species involved. They reach a length of 30 to 56 cm (12–22 in), with tails that are just as long as the body.
Like most New World monkeys, capuchins are diurnal and arboreal. With the exception of a midday nap, they spend their entire day searching for food. At night they sleep in the trees, wedged between branches. They are undemanding regarding their habitat and can thus be found in many differing areas. Potential predators include jaguars, cougars, jaguarundis, coyotes, tayras, snakes, crocodiles, and raptors, although there has only been one published observation of a predator taking a capuchin in the wild. The main predator of the tufted capuchin is the Harpy Eagle, which has been seen bringing several capuchins back to its nest.
The diet of the capuchins is more varied than other monkeys in the family Cebidae. They are omnivores, eating not only fruits, nuts, seeds, and buds, but also insects, spiders, birds' eggs, and small vertebrates. Capuchins living near water will also eat crabs and shellfish by cracking their shells with stones.
Social structure 
Capuchins live in groups of 10 to 40 members. These groups consist of related females and their offspring, as well as several males. Usually groups are dominated by a single male, who has primary rights to mate with the females of the group, though the white-headed capuchin groups are led by both an alpha male and an alpha female. Mutual grooming as well as vocalization serves as communication and stabilization of group dynamics. These primates are territorial animals, distinctly marking a central area of their territory with urine and defending it against intruders, though outer areas may overlap.
Life history 
Females bear young every two years following a 160 to 180 day gestation. The young cling to their mother's chest until they are larger, when they move to her back. Adult male capuchins rarely take part in caring for the young. Within four years for females and eight years for males, juveniles become fully mature. In captivity, individuals have reached an age of 45 years, although life expectancy in nature is only 15 to 25 years.
Capuchins are considered the most intelligent New World monkeys and are often used in laboratories. The tufted capuchin is especially noted for its long-term tool usage, one of the few examples of primate tool use other than by apes. Upon seeing macaws eating palm nuts, cracking them open with their beaks, these capuchins will select a few of the ripest fruits, nip off the tip of the fruit and drink down the juice, then seemingly discard the rest of the fruit with the nut inside. When these discarded fruits have hardened and become slightly brittle, the capuchins will gather them up again and take them to a large flat boulder where they have previously gathered a few river stones from up to a mile away. They will then use these stones, some of them weighing as much as the monkeys, to crack open the fruit to get to the nut inside. Young capuchins will watch this process to learn from the older, more experienced adults. It may take a capuchin up to 8 years to master this skill.
In 2005, experiments were conducted on the ability of capuchins to use money. After several months of training, the monkeys began exhibiting behaviors considered to reflect understanding of the concept of a medium of exchange that were previously believed to be restricted to humans (such as responding rationally to price shocks). They showed the same propensity to avoid perceived losses demonstrated by human subjects and investors.
When presented with a reflection, capuchin monkeys react in a way that indicates an intermediate state between seeing the mirror as another individual and recognizing the image as self.
Most animals react to seeing their reflection as if encountering another individual they don't recognize. An experiment with capuchins shows that they react to a reflection as a strange phenomenon, but not as if seeing a strange capuchin.
In the experiment, capuchins were presented with three different scenarios:
- Seeing an unfamiliar, same-sex monkey on the other side of a clear barrier
- Seeing a familiar, same-sex monkey on the other side of a clear barrier
- A mirror showing a reflection of the monkey
With scenario 1, females appeared anxious and avoided eye-contact. Males made threatening gestures. In scenario 2, there was little reaction by either males or females.
When presented with a reflection, females gazed into their own eyes and made friendly gestures such as lip-smacking and swaying. Males made more eye contact than with strangers or familiar monkeys but reacted with signs of confusion or distress, such as squealing, curling up on the floor, or trying to escape from the test room.
Theory of mind 
The question of whether capuchin monkeys have a theory of mind—whether they can understand what another creature may know or think—has been neither proven nor disproven conclusively. If confronted with a knower-guesser scenario, where one trainer can be observed to know the location of food and another trainer merely guesses the location of food, capuchin monkeys can learn to rely on the knower. This has, however, been repudiated as conclusive evidence for a theory of mind as the monkeys may have learned to discriminate knower and guesser by other means. Until recently it was believed that non-human great apes did not possess a theory of mind either, although recent research indicates this may not be correct. Human children commonly develop a theory of mind around the ages 3 and 4.
Relationship with humans 
Easily recognized as the "organ grinder" or "greyhound jockey" monkeys, capuchins are sometimes kept as exotic pets. Sometimes they plunder fields and crops and are seen as troublesome by nearby human populations. In some regions they have become rare due to the destruction of their habitat.
They are also used as service animals, sometimes being called "nature's butlers." Some organizations have been training capuchin monkeys to assist quadriplegics as monkey helpers in a manner similar to mobility assistance dogs. After being socialized in a human home as infants, the monkeys undergo extensive training before being placed with a quadriplegic. Around the house, the monkeys help out by doing tasks including microwaving food, washing the quadriplegic's face, and opening drink bottles.
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