A monkey is any of the 267 species of simian primates. The monkey family includes New World monkeys found in Mexico, Central America, and South America, as well as Old World monkeys that live in Africa, Asia, and Japan. Monkeys are intelligent and highly adaptable. They often move from one habitat to another, changing their diet as necessary to survive.
Most monkeys are diurnal (active during the day) but some, including baboons and geladas, are nocturnal. Most monkeys have long, flexible limbs that are well-adapted for their arboreal lifestyle. They also have highly-dexterous hands and feet with five digits that usually include toenails. The thumb on New World monkeys is generally in line with the other fingers, whereas Old World monkeys have more opposable thumbs.
In addition to a wide range of vocalizations, monkeys communicate with other members of their troop through facial expressions and body postures. They are also capable of learning new behaviors and using tools, such as rocks to open nuts.
Because they are highly adaptable, monkeys can often thrive in places where other animals cannot. However, this flexibility can also be a curse: humans have disrupted many monkey habitats, forcing them to travel farther to find food and shelter.
Most monkeys are social creatures that live together in groups called troops. The size of a troop can vary from a few individuals to several thousand. They are typically arranged into one-male groups, in which the dominant male rules over a group of females and unattached adult males. Troops usually maintain strong bonds through daily grooming, which is believed to express affection and build trust.