Evolution and Human Nature
The Evolution of Humans
•	Remains controversial
•	Methods
•	Fossils and physical features
•	DNA
•	Several “dead ends”
Darwin’s Theory (1859, 1871)
•	Major thrust simple to grasp
•	No larger purpose
•	Chance factors only
•	Philosophically a descendant of Hobbes
•	Two major mechanisms
•	Natural selection – slow but sure
•	Sexual selection – rapid but difficult
The Basic Idea
•	Individual members of species differ in some features
•	Some features affect reproductive success
•	Ability to live long enough to reproduce
•	Ability to find mate
•	Ability to provide for off-spring
•	Features that increase reproductive fitness
•	Will be passed to descendants if genetic
•	Need only slight advantages
Natural Selection
•	Animals compete
•	Against one another 
•	Food
•	Security
•	Another other species
•	Against environment
•	Features that affect reproductive success
•	Calibrated against all of these 
•	Need only slight advantages
Sexual Selection
•	Males (typically) compete for breeding privileges with females
•	Males features that may count against other males
•	Strength
•	Intelligence and cunning
•	Features that females may prefer
•	The peacock’s tail
•	Boot-strapping
Problems with Sexual Selection
•	Calibration against survival
•	Can produce features that are ecologically dysfunctional
•	Or otherwise useless
•	Requires evolution of female preference and male features simultaneously
•	Classically tends to ignore male preferences which are likely important
The Altruism puzzle
•	Darwin recognized that altruism might be dysfunctional
•	The revolution in kin selection
Human Evolution
•	The primate link
•	The humanoids
•	The Diaspora of sapiens
The Primate Connection
•	Most primates are violent from time to time
•	Male fighting
•	Infant killing by males
•	Violence toward females by males including rape
•	Chimps have raiding parties
•	But exceptions
•	Muriqui – South America
•	Bonobos
Explanations for primate Behavior
•	Most violence associated with
•	Breeding access
•	Or protecting parental investment
•	Tends to produce sexual dimorphism
Chimps 
•	Males fight
•	Only species besides humans that regularly kills adult con-specifics
•	Raiding parties and wars 
•	Male dominance behaviors toward females at adolescence
•	Rape
Gorillas
•	Males often kills infants
•	Usually when take over a harem
•	But about 15% of infants killed in this way
•	Male-male violence over breeding
•	Rarely rape
•	Dominance behaviors toward females but rarely violence
Orangutans
•	Large males fight over territory and breeding
•	Smaller males rape
•	Cannot compete with larger males
•	About 40% of all copulations are rape
Bonobos
•	Males fight but not fiercely
•	Females cooperate with one another and have equal status with males
•	Sex used as a bonding ritual
Do Primate Data Count?
•	Variable evidence but probably
•	Males likely to be competitive with one another
•	Originally perhaps for breeding privileges
•	But once physiological mechanisms set up this can become autonomous
But Some Cautions
•	And evolution has has had plenty to time to create differences since spilt with primates
•	No violence imperative or instinct as Lorenz and Freud suggested
•	Individual differences
•	Situational interactions
•	At best primate evidence suggests we have the potential to be violent
The Humanoids
•	Considerable debate about how fossils fit together
•	And with DNA and other micro-biological information which is most important
•	Huge debates about the exact lineage
Human Ancestors
Two Hypotheses About Human Diaspora
•	All agree that we started in Africa
•	The multi-evolution suggests early migrations 
•	The “out of Africa” suggests more recent migration
Two Hypotheses
Early migration
•	Evidence of h. Erectus (a probable ancestor of modern humans) 1.5-2 m in Java, China, Georgia
•	Different evolutionary lines
•	Can be used to support racial differences 
•	One reason has been unpopular
•	But physical differences need not produce mental
Out of Africa
•	Earlier migrations “overwritten” by later migrations
•	Within last 100,000 years
•	In most cases 60,000
•	Most physical evidence favors this hypothesis
•	Also migrants almost certainly meat eaters and fairly recent
Migrations from Africa
Genetic evidence
•	Mitochondrial Eve
•	Mitochondrial DNA accumulates mutations rapidly
•	Suggests a single female relative
•	About 200,000 years ago
•	Not only female alive
•	No proof in Africa, but where else?
Eve’s Family Tree

Other Genetic Evidence
•	Additional evidence from Y chromosome supports the “bottleneck”
•	Also have traced DNA across world
•	Africa has by far most DNA diversity suggesting oldest
•	Humans have about 10% of the diversity of chimps in terms of DNA
Pre-History in Europe
•	Ice age until about 30,000
•	H. Sapiens (Cro-Magnons) arrive about 30,000-40,000 ago 
•	Neanderthals still present
•	Some co-existence but no interbreeding
The Human Revolution
•	35,000-45,000 years ago and abrupt
•	Advances
•	More elaborate tools
•	Tools made from wider variety of materials
•	Transported raw materials over long distances
•	Constructed elaborate shelters
•	Cultural advances
•	Ornamentation
•	Art
•	Symbolic rituals

Evolutionary Psychology
•	Two main concerns
•	Evolution of mind
•	Evolution of social behavior
•	Also time frame
•	“Evolutionary time” maybe 200,000 years
•	Adaptations to that environment may not pay off now
•	Highly speculative
•	But careful to attach speculations to known principles
•	And stories are often quite convincing
•	Leads to important predictions
Evolution of Mind
•	Generally several disputes about this
•	Brain got much bigger
•	H. Habilis about 700cc (2m)
•	H. Erectus about 900 cc (1.8-.3m)
•	Neanderthals about 1400 cc (until 30,000_
•	Modern about 1300
•	Role of language?
•	Tools
•	Bipedal?
Brain getting bigger
The Argument About Modularity
•	Classic models of information processing
•	Built around computers
•	And general modules
•	But general processing can’t solve all our problems
•	Need several modules that combine in various ways
Some examples
•	Predator detection
•	Fast but false alarms?
•	Slow but accurate?
•	Maybe two systems
•	Food selection
•	Cooperation and altruism
•	Mate selection
•	Child rearing and teaching 
•	Cheater detection
•	Language Acquisition
Demands of Social Life
•	Reciprocal altruism and cooperation
•	Theory of mind
•	Language and communication
Reciprocal Altruism
•	In small groups helping can be directly reciprocated
•	But not in larger groups
•	Free rider problem and cheater detection
•	Detecting cheating
•	Basic emotions
•	Shame
•	Anger
•	Happiness
Theory of Mind
•	Behavior has meaning through intentions and goals
•	Thus have to understand what others are thinking
•	Assume their thought processes are like yours
•	The false belief test
•	Autistics
Language and Communication
•	Premium on people who can be clear
•	Has to be a specialized module for learning language
•	Kids learn despite many errors by models
•	Playing chess analogy
•	Have to know what is important
Sexual Selection and Gender
•	Both males and females “want” to produce as many offspring as possible
•	Should seek healthy and fertile partners
•	But each also has their own agendas
Male Signs of Fertility
•	Lack of disease – attractiveness
•	Testosterone produced physical features
Female Signs of Fertility
•	Lack of disease
•	Attractiveness
•	Correlated with body symmetry
•	And with health
•	Youth
•	Low waist to hip ratio
Differing Gender Agendas
•	Males can produce many children 
•	Should prefer multiple and many partners
•	And with young and fertile
•	Females can produce fewer children
•	Should invest in ones they have
•	Need protection and help from mate
•	And therefore should prefer males with strength and resources
•	Age
•	Testosterone – highest when ovulating
The Jealousy Argument
•	People should not expend resources on those with no genetic links
•	Women know whose children are theirs and should protect them
•	Jealousy directed at men who will not protect
•	Men emotionally involved with other women
•	Men can never be sure
•	Jealous of women involved sexually with other men
•	Less concerned with emotional infidelity
Murder and Abuse
•	Violence – to be discussed later
•	Men should be more likely to murder wives than reverse – true
•	Men should be more likely to murder stepchildren than own – true
•	When women murder children
•	One of twin
•	Later born
•	Younger mother
Cognitive Differences Associated with Gender
•	Men better at spatial skills because of hunting requirements
•	Women better at verbal and communication
•	Women bound to be more involved with child-rearing
•	Better communication skills
•	Better emotional reading
Evaluation of Evolutionary Psychology
•	Exciting way to summarize
•	New predictions supported by data
•	But…
•	Over-extended
•	Not tightly derived
•	And usually other explanations
•	Based on psychology
•	Based on ecology – the cooking “gene”