The question of which primate group is most closely related to humans is one that is debated amongst biologists and primatologists alike.

While some believe that the order of primates can be organized in a simple and straightforward way, others argue that it is a much more intricate and complex system. In this article, we will explore the various primate groups, their characteristics, and the evidence pointing to which one is most closely related to humans.

What Are Primates?

Primates are an evolutionary order of mammals that include a wide array of animals such as monkeys, apes, bushbabies, mouse lemurs, and humans. These animals are typically characterized by their complex brains and hands with opposable thumbs that allow them to perform complex tasks and use tools. These features, when combined with their varied lifestyles and behaviors, mean that primates have become some of the most successful animals on the planet.

Different Groups of Primates

Primates can generally be classified into three distinct groups: prosimians, New World monkeys, and Old World monkeys and apes. Below, we will take a look at each of these groups in greater detail:


Prosimians are the earliest branch of the primate evolutionary tree, and they are characterized by their small size, nocturnal behavior, and low levels of cognition. This group of animals includes lemurs, tarsiers, and bushbabies and is believed to be the most primitive of the three groups.

New World Monkeys 

New World monkeys are found in South and Central America and tend to be small and arboreal, meaning they spend most of their time in trees. While their brains are smaller than those of other primates, they are still relatively complex and are capable of learning, problem solving, and self-recognition.

Old World Monkeys and Apes 

Old World monkeys and apes encompass a wide range of primates and include species such as baboons, capuchins, and macaques. These animals are typically larger than the other groups and are more versatile in terms of their locomotion, able to swing from branch to branch, walk and run on four limbs, and even stand on two feet. They also have significantly larger and more complex brains, allowing them to exhibit complex behaviors such as tool usage, social learning, and even language.

Comparative Anatomy 

When comparing the various primate groups, one of the most important distinguishing characteristics is the anatomy of the skull and skeleton. Prosimians, for example, are characterized by their elongated lower jaw and some of the smallest brains in the primate order. New World monkeys, on the other hand, have a short skull, larger brains, and curved finger and toe bones suited for arboreal locomotion.

The skull of Old

World monkeys and apes, on the other hand, is much more elongated and their brains are larger and more complex, with a well-developed prefrontal cortex. This allows them to exhibit more complex behaviors such as tool usage and language. In addition, apes have a more human-like build with longer legs, shorter arms, and shorter muzzles.

Which Group Is Most closely Related to Humans?

Now that we have looked at the various primate groups and their comparative anatomies, it should be relatively easy to determine which one is most closely related to humans. The answer, of course, is the Old World monkeys and apes.

Comparing the skulls and skeletons of humans to those of the other primate groups reveals a great deal of anatomical similarities. Humans, like Old World monkeys and apes, have an elongated skull, a prefrontal cortex, and a more human-like body build. In addition, humans are the only primates who have fully-opposable thumbs, allowing them to craft and use tools.

It is clear, then, that Old World monkeys and apes are the primates most closely related to humans. This conclusion is supported not only by both their skulls and skeletons, but also their behaviors, which closely mirror those of humans. Ultimately, this similarity is what makes primates such fascinating and important animals, and why it is essential that we continue to study them in order to better understand our own evolution and behavior.