Primates: Definition, Evolution & Characteristics

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  • 0:00 Primate Definition
  • 0:43 Evolution
  • 2:30 Prosimians
  • 4:33 Simians
  • 5:52 Apes and Humans
  • 7:34 Lesson Summary
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Lesson Transcript
Instructor: Nicholas Gauthier
Primates, including apes, monkeys and prosimians, make up our extended family tree. New and exciting fossils have expanded our understanding of this peculiar group to which we belong. Learn more about our closest cousins in the animal kingdom.

Primate Definition

Primates is the name of the order of mammals to which we happen to belong. The name means 'first' or 'most important' and was given to the order by Carl Linnaeus. While naming it that way may have been a matter of human ego, we can't help but feel a certain fascination with the group to which we belong.

Primates typically have grasping hands and feet in addition to relatively large brains. They have flatter faces than most other mammals, lacking the muzzle of dogs, bears, deer and other mammals. They have good vision but a more limited sense of smell than most other mammals. Most are highly social.


Primates may have evolved from insectivores, or animals that live off insects. The primate family tree itself goes back at least 55 million years. We know this because fossils classified in the genus Archicebus are believed to date back to the late Cretaceous Period, just before the end of dinosaurs.

The most primitive living primates are called prosimians. They are primitive in the sense that they retain characteristics of the very first primates from millions of years ago. Prosimians include lemurs, lorises, galagos and tarsiers.

The other main group of primates, the simians, likely evolved after the prosimians. This group includes the new world monkeys, which have tails and are considered to be relatively primitive. These monkeys are native to North and South America, aka the 'New World.' Many have prehensile tails, which is an adaptation that few other primates share.

The rest of the simians, called anthropoids, include old world monkeys, apes and hominids, including humans. Old world monkeys evolved first, followed by apes and then hominids. These species are native to Europe, Africa and Asia.

This family tree shows the origin of primates, as well as the time when each major primate group split off on its own evolutionary branch.

The family tree of primates.
Primate Family Tree

As you can see, prosimians developed first, followed by simians. To put it differently, lemurs and lorises' ancestors branched off first, followed by tarsiers, then new world monkeys, then old world monkeys, then apes. Humans came about relatively late in the game.


There are four main groups of prosimians: galagos, lemurs, lorises and tarsiers. Prosimians' brains are not exceptionally large compared to other mammals. Most have wet, dog-like noses.

Galagos are fast, agile jumpers that live in Central Africa. They can leap very far for their size and tend to hunt insects. They are nocturnal and probably evolved in that niche to avoid competition with other primates. Galagos have good night vision, excellent hearing and long tails for balance. They tend to be far faster and more active than lorises and tarsiers. Galagos are often called bush babies.

A galago, native to central Africa.

Lemurs live exclusively in Madagascar, although their fossils are found on mainland Africa. They have wet noses like dogs and a keen sense of smell. Lemurs range greatly in size, from the tiny mouse lemur to the 20-pound indri. At present, there are about 50 recognized lemur species. Their diversification into many species within a relatively small habitat was the result of resource partitioning. This process occurs when food and habitat are limited, so animals specialize in their diet and behavior.

The tiny mouse lemur.
Mouse Lemur

The highly social ring-tailed lemur, a zoo favorite.
Ring-tailed Lemur

The indri, whose call is hauntingly beautiful, like whale song.

Lorises are slow-moving, nocturnal primates that mostly eat insects. They have large eyes and a distinct appearance, with grasping hands and feet that wrap around branches. There are about ten species living in India and Southeast Asia.

The nocturnal slow loris.
Slow Loris

Tarsiers are also generally nocturnal. While considered prosimians, they are actually genetically closer to simians than to the other prosimians. One trait that sets them apart from other prosimians is their dry nose. Tarsiers have strong hind legs for jumping after prey. They also have very large eyes that are as large as their brains. Their eyes are so large that they cannot turn them, but they can turn their heads around like owls.

Tarsiers in a tree.


Simians include monkeys, apes and hominids. They have less of a sense of smell than prosimians but bigger brains.

New world monkeys live in North and South America. Some new world monkeys have prehensile tails that let them grasp tree branches. Most lack opposable thumbs. Their nostrils face out to the side. Most are also arboreal, living in trees. They tend to be more monogamous than old world monkeys and show more intense parental care.

New world monkeys range in size from the 6-inch pygmy marmoset to the 30-pound southern muriqui. There are five living families of new world monkey.

The brown spider monkey, a typical new world monkey with a prehensile tail.
Brown Spider Monkey

Anthropoids are old world simians. These include old world monkeys, apes and hominids. Anthropoids are considered to be the most advanced primates.

Old world monkeys have downward-facing nostrils. Some are arboreal, but many live on the ground. They range in size from the talapoin, which weighs about 3 pounds, to the mandrill, which can weigh more than 100 pounds. Some old world monkeys lack tails. None of them have prehensile tails, which would be used for grasping, like the tail of a possum.

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