Hominid Evolution Crystal A. Brandon

Evolutionary Relationship Amongst Hominid Species

Emergence of Hominid Species

Hominid Brain Evolution Estimation of Values in Figure 3.4 of text

Important Brain Changes Across Hominid Species Increase in brain volume across species of Australopithecines Substantial changes in facial structure of Homo Expansion of frontal and parietal lobes of H. habilis Continued expansion from emergence of H. erectus to modern day humans

Encephalization Quotient An index of brain size relative to that of an average mammal of the same body weight Ex. Chimps = 2.0 Humans = 5.0 to 6.0, on average

Adaptation & Selection Pressures: Climatic Pressures Turnover Pulse Hypothesis (Vrba, 1995) Hypothesis: Large scale climatic changes result in habitat and ecological changes, resulting in pulses of speciation and extinction

Adaptation & Selection Pressures: Ecological Pressures Focus on the ability of hominids to extract biological resources from the ecology improving survival prospects and support population increases and expansion Superpredator: greater ability to capture and process Patterns of migration & mass extinctions of species Evidence in nonhumans species: Foraging and complex predatory demands correlated with larger brain volume and higher EQ

Adaptation & Selection Pressures: Ecological Pressures Kaplan et al. (2000): Hypothesis If the ability to extract and process biological resources was the driving force in the evolution of brain and cognition, then improvements in the ability of hominids to extract these resources should corresponds to changes in brain volume and EQ during hominid evolution. Ex. Fire and sophisticated tool use

Adaptation & Selection Pressures: Social Pressures Ecological Dominance The ability to very efficiently extract biological resources from the ecology and manipulate the ecology in ways that: 1. reduce mortality risks 2. support subsequent population expansions Alexander (1989): Ecological pressures were more prominent earlier in hominid evolution, and social pressures more prominent later in hominid evolution

Social Complexity & Ecological Dominance Ecological Dominance: Control of Survival-Related Resources Supporting Traits Brain and CognitionSociality and Behavior Folk BiologyFolk Physics Hunting/Foraging/Ecological Manipulation Co-evolving Traits: Function to Adapt Supporting Traits to Local Ecology Increased Parental InvestmentIncreased Developmental Activity

Social Complexity & Ecological Dominance Increase in Paternal Investment Increase in length of developmental period Increased Developmental Activity More opportunities to practice hunting and foraging

Social Dynamics & Ecological Dominance Social Dynamics: Social Struggle for Control of Survival and Reproduction-Related Resources Supporting Traits Brain and CognitionSociality and Behavior Co-evolving Traits: Function to Adapt Supporting Traits to Local Ecology Increased Parental InvestmentIncreased Developmental Activity Folk Psychology Kinship Networks Reciprocal Relationships

Social Dynamics & Ecological Dominance Kinship groups in competition with other kinship groups over resources and reproduction Kinship groups facilitate: 1. Peer relationships 2. Rough-and-tumble play

Forms of Social Conflict and Competition Intrasexual Competition Male-Male Competition Within Group and Between Group Competition for Control of Resources and Position Female-Female Competition Intersexual choice Male Choice Female Choice Within group competition often involving subtle manipulation of other members to gain access to resources Family Relationships Spousal Parent-offspring and sibling Men will be selective in their choice of a mate because of paternal investment and paternal certainty Women will select their mate based on male social status and male paternal competency Conflict over maternal vs. paternal investment; resource control; and marital fidelity Extended developmental period results in conflict over parental allocation of resources

Motivation to Control Human motivation to control focuses on attempts to control: 1.Social Relationships: Benefits? - protection, territorial gain, shared access to resources 2.Other People: Benefits? - reproductive potential, social power, access to resources 3.Biological and Physical Resources: Benefits? - healthier, inherited strategies to obtain resources

Evolutionary Mechanisms to Support Motivation to Control Conscious-psychological mechanisms Affective mechanisms Cognitive mechanisms