Hominid Evolution

Crystal A. Brandon

Evolutionary Relationship Amongst Evolutionary Relationship Amongst Hominid SpeciesHominid Species

Emergence of Hominid Species

Hominid Brain Evolution

0

200

400

600

800

1000

1200

1400

Bra

in V

olu

me

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 Cognition Sociality and Behavior

Folk Biology Folk Physics Hunting/Foraging/Ecological Manipulation

Co-evolving Traits:

Function to Adapt Supporting Traits to Local Ecology

Increased Parental Investment Increased 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 DominanceSocial Dynamics:

Social Struggle for Control of Survival and

Reproduction-Related Resources

Supporting Traits

Brain and Cognition Sociality and Behavior

Co-evolving Traits:

Function to Adapt Supporting Traits to Local Ecology

Increased Parental Investment Increased Developmental Activity

Folk Psychology Kinship NetworksReciprocal

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 CompetitionMale-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