Primate Behavior and Human Origins

Glenn King

• Publisher: Taylor & Francis
• Year: 2015
• Print ISBN: 9781032512204
• eBook ISBN: 9781317526650
• Edition: 1
• Topic: Social Sciences
• Subtopic: Anthropology
• Index: Social Sciences

This comprehensive introduction demonstrates the theoretical perspectives and concepts that are applied to primate behavior, and explores the relevance of non-human primates to understanding human behavior. Using a streamlined and student-friendly taxonomic framework, King provides a thorough overview of the primate order. The chapters cover common features and diversity, and touch on ecology, sociality, life history, and cognition. Text boxes are included throughout the discussion featuring additional topics and more sophisticated taxonomy. The book contains a wealth of illustrations, and further resources to support teaching and learning are available via a companion website. Written in an engaging and approachable style, this is an invaluable resource for students of primate behavior as well as human evolution.

1
The Primates

Meet Your Relatives

What’s that thing? A monkey? An ape? It looks like my grandpa.

There are several hundred species of primates in the world today. Together they constitute what zoologists call an order of animals, which is a group with a common ancestor dating back tens of millions of years. This chapter surveys the primates in terms of their biological features, evolutionary origins, and main subgroups. The figures in this chapter and the next will illustrate the diversity of the primates.

Primate Biology and Behavior

Anatomical traits facilitate some behaviors and limit others. Wings make flying possible for most birds, but the reduced wings of ostriches show that flight is no longer possible for them. Physiology is also crucial: hormonal secretions (e.g. testosterone) and neurological processes shape behavior and vice versa. Biological traits raise issues of function and behavior, i.e. how the traits work and what the results are. For instance, birds must flap their wings in order to fly. Complex neurophysiological processes underlie the motivation to eat that we call hunger.

Common Primate Traits

Primate characteristics are illuminated by knowledge of the order’s mammalian heritage. Some of these characteristics are shared, such as internal temperature regulation (warm bloodedness), live birth, and milk secretion. Other primate features contrast with those of most other mammals (Box 1.1). Some of these have been retained while other mammals changed. For instance, the five digits on each hand and foot contrast with specializations such as paws and hooves. Some distinctive primate traits are unusual innovations, such as the location of the eyes.

Compared to most other mammals, primate eyes are located closer together and toward the front of the head. This produces binocular vision, the ability to fix both eyes on the same thing simultaneously (Figure 1.1). The result is depth perception: getting two views of the same object allows the brain to calculate the distance to that object. Primates as a group have the largest binocular visual fields among mammals (Heesy 2004). Large eyeballs also enhance primate vision, and the visual centers in the brain are correspondingly large and complex.

Box 1.1 Distinctive Primate Traits

This table summarizes important features that are common among primates and relatively rare among other mammals. The broadly functional categories emphasize connections with behavior.

Grasping

• mobile digits, especially first digits of hand and foot
• flattened nails on some or all digits
• friction surfaces on tips of digits
• sensitive nerve endings on the surfaces of appendages.

Locomotion

• long, muscular legs
• hindlimb dominance (for both braking and acceleration).

Senses

• orbital convergence (for binocular vision)
• postorbital bone structure (protection of the eye).

Dentition

• four types of teeth: incisors, canines, premolars, molars.

Figure 1.1 A greater galago focuses its binocular vision. © Y.A. de Jong and T.M. Butynski, www.wildsolutions.nl

The orbits are the bony sockets that hold the eyes, and orbital convergence is a term for the relative closeness of primate eyes. Primate orbits are reinforced by extra bone at the rear that replaces the tough fiber found in most other mammals. This orbital closure creates a complete ring of bone around each eye and functions as protection against external dangers and/or unusual chewing stresses. Eye damage and loss are more critical for primates than for many other animals.

Primates are largely arboreal, meaning that they conduct most or all of their activities in trees. Their typical climbing pattern is distinctive. Rather than digging in with claws, they grasp with flexible extremities that can be called hands and feet rather than paws (Figure 1.2). Flat nails in place of claws support the fingers and toes. The five digits on each hand and foot (called pentadactyly) can be spread to facilitate gripping. Grip is further enhanced by friction surfaces with curved ridges on the digits and on the palms and soles. The term dermatoglyphics can be used for both the skin patterns and the study of them. Nerve endings in these surfaces provide feedback on how the appendages are interacting with the environment.

The hallux (the same digit as the big toe in humans) is widely divergent in virtually all primates and is capable of a pincer-like grasp more powerful than that of the hands (Figure 1.3). In many primates the thumb is opposable to some extent: it diverges from the other digits and can rotate to make some degree of contact with them. Primates use their flexible hands and feet to grasp all sorts of objects, from branches to food items.

Primate limbs are also flexible. Paired bones in the forearms and lower legs allow a higher degree of rotation than in other mammals. The collarbone (absent from many other mammals) is a strut that allows the arm to rotate into a variety of positions. Climbing creates a tendency toward vertical posture, which also distinguishes primates from the majority of mammals.

Figure 1.2 A red-bellied lemur demonstrates its grasping ability. © Stacey Tecot

Figure 1.3 A chimpanzee shows its opposable hallux, the primate equivalent of the human big toe. © Curt Busse

Primates appear to resemble other mammals in being quadrupedal, broadly defined as walking on four limbs on a relatively level surface (Figure 1.4). However, many components of primate quadrupedalism are especially suited to arboreal movement (Schmitt 2010). During each step the animal bends its arms and legs. This flexion reduces stress on the limbs (Larney and Larson 2004). It results in a crouching posture when walking on branches, which lowers the center of mass and enhances balance. Features of the primate hindlimbs and ankles facilitate leaping.

The primate forelimb is used for foraging and other manipulations, as well as diversified locomotion (any movement from one place to another). This requires mobility at the expense of stability, which makes the forelimb more vulnerable to stresses. Limb flexion alleviates some stress, but hindlimb dominance is also a factor: while most mammals place the greater part of their weight on the forelimbs, the distribution in most primates is roughly equal or is greater on the hindlimbs (Hanna et al. 2006). During arboreal movement the rear legs provide propulsion and a resting foundation, while the forelimbs provide guidance (Schmitt 2010).

Primates can process diverse foods because they have retained four kinds of teeth from their mammalian ancestors. The front teeth perform a variety of grasping functions. Incisors, relatively thin and flat, are used for nipping. The pointed canines can be used for fighting as well as food processing actions such as stripping bark. Premolars and molars (cheek teeth) are essential for chewing. Each has protruding structures, typically three or four, called cusps. Cheek teeth can pierce food with the cusps, shear with crests that link the cusps, and crush or grind between the occlusal surfaces. The pattern of molar cusps and their low profile in primates enhance crushing at the expense of other actions. This allows primates to obtain greater nutritional benefits from hard or tough foods such as nuts, seeds, roots, and insects with hard exoskeletons.

Figure 1.4 A captive monkey on a net displays the flexed limbs and crouching posture of arboreal locomotion. © Jaydenwong via iStock

The number of teeth in each category varies among primates. The typical array for a particular group is expressed by a dental formula that represents one side of the mouth, upper and lower. For example, the human dental formula is 2.1.2.3 / 2.1.2.3. Each quadrant of the jaw contains two incisors, one canine, two premolars, and three molars. Although some human individuals never grow third molars, this simply exemplifies the variation that exists in virtually every biological trait.

Primate Evolution and Classification

Evolution, as Darwin wrote, is descent with modification: the biological features of a group of organisms undergo hereditary changes across generations. There are several causes of evolutionary change but we will be concerned with natural selection, a process in which traits that favor successful reproduction become more common.

Evolution and Natural Selection

In modern terms evolution is a process of change in the characteristics of a breeding population, a group of organisms capable of reproductive interaction. Visible changes are the result of shifts in the gene pool, which is the totality of genes that are circulating among the members of the population, from one generation to the next. Evolution affects anatomy, which shapes and limits behavior, and affects behavior more directly through changes in the brain and the endocrine system.

Natural selection is an evolutionary process in which some genes become more or less common over generations because the traits that they influence affect reproductive success. Individuals who have more offspring than others in the same population because of genetic differences will transmit more genes to future generations, with the proviso that their offspring are viable (i.e. they can also reproduce). As a result of this process, the genes in question become more common and may ultimately be found in all members of the population.

Natural selection takes place in varied environments, so it usually favors traits that result in survival and reproduction in a certain kind of animal in a certain setting. An angry rabbit that fights a bobcat will probably do this only once. Rabbits that become frightened and run away are more likely to survive and reproduce. Those that start sooner and run faster are the ones most favored by natural selection. They transmit the genes underlying their anatomy and behavior to the next generation. Contrary to a widespread misunderstanding, it is the members of the same population (rabbits in this case) who compete for reproductive success. Predators (e.g. bobcats) are not competitors—they are part of the environment.

Evidence for evolution includes fossils, the physical remains of living things. Most of them are bones or teeth preserved by mineralization. However, fossils can also be other signs of the past, such as footprints. The fossil record has many gaps, so comparison of rela...

Table of contents

• Cover
• Title
• Copyright
• Dedication
• Contents
• List of figures
• Preface
• Acknowledgements
• Introduction
• 1 The Primates: Meet Your Relatives
• 2 The Study of Primate Behavior
• 3 Primate Ecology and Behavior: Common Features
• 4 The Strepsirrhine Suborder
• 5 The Lorisiform Infraorder: Strepsirrhines in the Dark
• 6 Lorisiform Variation: Leapers and Creepers
• 7 The Lemuriform Infraorder: Island Refuge
• 8 Lemuriform Variation: The Night Life
• 9 Lemuriform Variation in the Light of Day
• 10 The Tarsioid Suborder: Common Features and Variation
• 11 The Anthropoid Suborder: Monkeys and Apes
• 12 The Platyrrhine Infraorder: New World Monkeys
• 13 Platyrrhine Variation: Atelids and Pitheciids
• 14 Platyrrhine Variation: Cebids
• 15 Cebines: Squirrel Monkeys and Capuchins
• 16 The Catarrhine Infraorder: Old World Monkeys and Apes
• 17 The Cercopithecoid Superfamily: Old World Monkeys
• 18 Cercopithecoid Variation: Leaf Eaters and Cheek Pouchers
• 19 A Cercopithecine Tribe: The Guenons
• 20 A Cercopithecine Tribe: The Papionins
• 21 Genus Papio: The Real Baboons
• 22 The Hominoid Superfamily: Apes Small and Large
• 23 Great Apes of Asia: Orangutans
• 24 Great Apes of Africa: Gorillas
• 25 Great Apes of Africa: Common Chimpanzees
• 26 Bonobos: Lightweight Chimpanzees
• 27 Human Origins: The Last Common Ancestor
• 28 Early Hominin Evolution: The Australopiths
• 29 Our Evolutionary Heritage: The Primate in Us
• 30 Primate Conservation: Will Any Be Left?
• Glossary
• Index