Introduction

Maybe you just watched a film about Madagascar and met some lemurs jumping and running through the forest. Maybe you visited the zoo and saw gorillas grooming each other and eating leaves. Maybe you passed an elementary school and saw kids swinging on the monkey bars. Or maybe you just looked at your thumb as you picked up a carrot to eat it and thought “wow, that’s pretty cool I can pick things up like that!” In all these scenarios, you are contemplating what it means to be a primate.

See Morbeck, Galloway and Zihlman's book The Evolving Female for more on what it means to be a mammal and how primates build on those mammal characteristics

So What Makes a Primate a Primate?

We look at THREE kinds of evidence:

• Related to TEETH and SNOUT
• Related to EYES and EARS
• Related to ARMS and LEGS
• Related to FINGERS and TOES

Primate Evolutionary Trends

Primate Behavior

SKELETAL FEATURES

Related to TEETH and SNOUT

• Shortened snout - Why? Primates rely less on their sense of smell and more on vision. Primates also have a reduced number of teeth as compared to other mammals. LOOK AT the shortened snout on the Vervet monkey (Cercopithecus aethiops) on the left.
• Several types of teeth: inisors, canines. premolars, molars - Why? With different types of teeth, can eat a variety of foods and process food efficiently.  They have incisors for biting, canines for shearing and premolars and molars for crunching food into digestable packages. LOOK AT the tooth display of another Vervet monkey (Cercopithecus aethiops) on the right.

Related to EYES and EARS

• Forward facing eye orbits - Why? Primates have an increased emphasis on vision, so natural selection acted to position the eyes best for taking in the most visual stimuli. LOOK AT the forward facing orbits on this chimpanzee (Pan troglodytes schweinfurthii) on the left.
• Steroescopic vision - Why? Stereoscopic vision means that the fields of vision provided by each eye overlap, resulting in what's called depth perception. This is extremely useful for forest-dwelling promates, as it lets them judge how far away the next branch is as they are moving from tree to tree
• Three bones of the middle ear housed in a skull outgrowth (the auditory or petrosal bulla)

Related to ARMS and LEGS

• Clavicles (collarbones) - Why? Primates have very extensive shoulder motion because the clavicle provides the only bony link between the upper limb and the trunk
• Two separate bones in the forearm and lower leg - Why? Having two bones allows for better limb motion and more precise movements

Related to FINGERS and TOES

• Nails instead of claws - Why? Nails allow primates to manipulate objects more easily
• Increased thumb mobility - Why? Again, related to manipulating objects. As you move across the primate order from lemurs and lorises to great apes, including humans, the thumb becomes more and more mobile. LOOK AT the olive baboon (Papio anubis) manipulating what he is eating with his mobile thumbs below on the left.
• Grasping feet - Why? Primates have more big toe mobility for grasping and climbing. The only exception is humans (Homo sapiens). We have lost the grasping ability in our feet because our feet are designed to serve as a platform for walking. LOOK AT the grasping foot of the mother ring-tailed lemur (Lemur catta) pictured below on the right.

PRIMATE EVOLUTIONARY TRENDS

• Trend toward more vertical posture - Why? Primates tend to move with a more vertical posture, even if they are rarely upright. LOOK AT the Indri (Indri indri) who moves by clinging to one tree trunk and and leaping to another, pictured on the top left below.
• Trend toward different use of forelimbs and hindlimbs - Why? Primates do more than just walk with their limbs. As you can see on the left above, where the baboon is eating some meat, primates use their hands to bring food to their mouths, instead of eating just with their mouth like a cat or dog.
• Trend toward longer lives with longer periods of infancy, childhood and adulthood - Why? Longer lives and longer life stages are good for increased growth, especially brain growth. Primates have larger brains for their body size than a lot of other mammals, and are born with brains that still need to develop quite a bit outside of the mother’s body. Primates also spend a lot of time learning skills and strategies for food gathering and survival from their mothers and others in their social groups. LOOK AT the mother chimpanzee (Pan troglodytes schweinfurthii) with her day-old daughter, pictured on the bottom left below.
• Trend toward enlarged brains with increased areas for vision and reduced areas for olfaction

PRIMATE BEHAVIOR

So what do primates DO that makes them primates? They spend time

• Using their limbs to climb in trees by grasping with hands and feet LOOK AT the drawing of a galago (Euoticus elegantulus) below left, moving along a tree  
• Using their hands to bring food to their mouth for feeding
• Being a part of social group life, building and reinforcing bonds between individuals and learning from their mothers and others