Chapter 8 Primate Models For Human Variation

Chapter Outline  Human Origins and Behavior  Brain and Body Size  Language  Primate Cultural Behavior  Aggressive Interactions Between Groups  Affiliation, Altruism, and Cooperation  The Primate Continuum

Human Origins and Behavior  Humans and chimpanzees share more than 98% of their DNA, yet contrast in aspects of anatomy and behavior.  Behavioral and anatomical adaptations were selected for as early hominids spent more time on the ground and exploited different food resources.

Brain and Body Size  The relationship between body and brain size is expressed as the index of encephalization.  Most primates have brain sizes close to their expected values given their body sizes.  Modern humans have a brain size much larger than expected for their body weight.  Early members of the genus Homo, as well as Australopithecines were not as encephalized as modern humans.

Brain Growth and Development  In nonhuman primates, the most rapid period of brain development occurs either before or immediately after birth.  In humans, brain growth occurs before and after birth, resulting in greater brain expansion during the first year after birth.

Developmental Changes in the Skulls of Chimpanzees and Humans

Primate Language Abilities  Social interactions and problem-solving abilities demonstrate primate intelligence.  Vervet monkeys have three different vocalizations to indicate types of predators.  The fact that apes can’t speak has more to do with their anatomy and the language related structures of the brain than intelligence.

Development of Language Abilities  Ape language experiments suggest that the earliest hominids must have had ape-like communicative abilities.  We don’t understand why communication became increasingly important in the hominid lineage, and why natural selection acted to enhance our ancestors’ ability to use spoken language.

Evolution of Human Language

Criteria for Cultural Acts in Other Species InnovationNew pattern is invented or modified. DisseminationPattern is acquired (through imitation) by another from an innovator. InnovationNew pattern is invented or modified. DisseminationPattern is acquired (through imitation) by another from an innovator.

Criteria for Cultural Acts in Other Species Diffusion Pattern spreads from one group to another. TraditionPattern persists from innovator’s generation to the next. NonsubsistencePattern transcends subsistence. NaturalnessPattern is shown in absence of direct human influence.

Nonhuman Primate Cultural Behavior  Cultural behavior is learned and passed from one generation to the next.  Chimpanzee culture includes tools such as termite fishing sticks and leaf sponges.

Aggression  Primates might defend a core area within their permanent home.  Jane Goodall witnessed unprovoked, brutal attacks of chimpanzees by other chimpanzees.  Territoriality and acquisition of females are the motives suggested for chimpanzee male aggression.

Altruism  Altruistic behaviors benefit another while involving some risk to the performer  The majority of altruistic acts consist of the mother protecting her offspring.  Primates deviate somewhat from this pattern in that the recipient and the performer of the altruistic acts may not be closely related to each other.

Cooperative Behaviors  Include alliances, coalitions, and grooming partnerships.  Chimpanzees form alliances to increase their status or to gain protection from others.  Chimpanzees frequently cooperate with each other in hunts.  The patterns of cooperation in chimpanzee hunting behavior may provide clues to the development of human hunting behavior.

The Primate Continuum  Human brains are larger than primate brains, but the neurological processes are functionally the same.  That humans are part of an evolutionary continuum is the basis for animal research, yet we cage nonhuman primates with little regard for their needs.  Nonhuman primates should be maintained in social groups and introduced to habitat enrichment programs.

Primate Behavioral Models for Human Evolution