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Hominid Evolution
Crystal A. Brandon
Evolutionary Relationship Amongst
Hominid Species
Emergence of Hominid Species
Hominid Brain Evolution
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Brain Volume
1200
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
Folk Biology
Folk Physics
Sociality and Behavior
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
Dominance
Social Dynamics:
Social Struggle for Control of Survival and
Reproduction-Related Resources
Supporting Traits
Brain and Cognition
Sociality and Behavior
Kinship Networks
Folk Psychology
Reciprocal
Relationships
Co-evolving Traits:
Function to Adapt Supporting Traits to Local Ecology
Increased Parental Investment
Increased Developmental Activity
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
Female-Female
Competition
Within Group and Between Group Competition for Control of
Resources and Position
Within group competition often involving subtle manipulation of
other members to gain access to resources
Intersexual choice
Male Choice
Men will be selective in their choice of a mate because of
paternal investment and paternal certainty
Female Choice
Women will select their mate based on male social status and
male paternal competency
Family Relationships
Spousal
Parent-offspring
and sibling
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