Chapter 8
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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.
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.
