Psych 124: The Evolution of Human Behavior on

Intro to Evolution

Mon, 01 Jan 0001 00:00:00 +0000

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Intro to Evolution #

Evolution is History: #

What ancestors did for a living
- north vs south cultural differences = farmers vs. herders

The goal of studying evolution: #

Understand why humans behave similarly to animals
much of human behavior can be explained w/ classic evolutionary principles
humans are uniquely shaped by adaptations for culture
culture has shaped human genetic evolution

How to study human behavior #

Behavior is shaped by:

Culture and Evolution

Mon, 01 Jan 0001 00:00:00 +0000

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Culture and Evolution #

Why are humans so successful? #

Compared to other animals, humans appear fragile, weak

1. We ate all the big animals #

Extinction of megafauna correlated w/ arrival of humans

2. Only 1 species of great ape survived? #

Genetic variation among humans very low

-1. Not because of our intelligence #

Europeans on expeditions often starved, while indigenous tribes thrived
- Example: Burke & Wills expedition -> died by starvation b/c they didn’t know how to process the local foods, despite being “highly trained” and educated by European Standards

3. Culture #

Humans can survive anywhere, as long as we have past knowledge
Example: Lost woman of Catalina (Juana Maria) -> well adapted and flourished in native environment, but died of dysentery after being “rescued” by colonizers

Dual-Inheritance Theory #

Genes influence behaviors, behaviors influence genes

WEIRD

Mon, 01 Jan 0001 00:00:00 +0000

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WEIRD #

Western
Educated
Industrial
Rich
Democratic

→ 12% of humans are WEIRD, but 97% of psychological studies have WEIRD subjects

Effects on Visual Perception and Thought #

Müller-Lyer illusion: only affects Western cultures ⟷ ⟩—⟨
- homogeny of illusion: carpenters
Spatial reference:
- egocentric orientation (left/right relative to self) → box + stick experiment
- vs allocentric orientation: NSEW
holistic thought: self is dependant on group

Cumulative Culture

Mon, 01 Jan 0001 00:00:00 +0000

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Cumulative Culture #

Why do humans have so much cumulative culture? #

Mechanism: neurons fire when observing/learning from actions Ontogeny: humans imitate and learn from a young age Function: necessary for survival: collaborative hunting, harming Phylogeny: we are haplorhines (Old World Monkeys), diurnal + group oriented

Study: are humans smarter than apes? #

compared adult apes to 2 yo humans
physical cognition
- space: look for reward
- quantity, addition of objects
- causality: production, tools
social cognition
- social learning (imitation)
- communication: gestures, etc.
- theory of mind: other humans are conscious

humans are more predisposed to copying, even if it may not be strictly necessary (mirror neurons) whereas apes ignore ‘useless’ tasks

Criteria for Teaching #

Teacher modifies behavior in presence of pupil
No immediate return for teacher
Teacher encourages, punishes, sets examples to modify pupil’s behavior
Pupil acquires knowledge more rapidly
- first observed example: ants tandem walking (2005)
- mammals: meerkats learn how to eat scorpions without getting hurt
- more prevalent in captivity

Repertoire of Cultural Transmission Strategies #

social tolerance: teacher grants learners access to close observation

Evolutionary Thought

Mon, 01 Jan 0001 00:00:00 +0000

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Evolutionary Thought #

History of Evolutionary Thought #

pre-darwin: transmutation of species occurred, but no hypothesis of mechanism
- Oswald Avery, Crick + Watson: 1940s discovery of DNA

Natural Selection: #

individuals vary in phenotypes
phenotypic variation transmitted to offspring
competition for scarce resources

Consequence: offspring w/ favorable traits have more offspring, ⇒ adaptation by natural selection

Darwin and Natural Selection #

5-year voyage on Beagle as naturalist
Galapagos islands:
- founder effect: evolution depends on small group of species who happened to arrive. first arrivers = little competition ⇒ more
- adaptive radiation: diversification
  - Syms Covington unto locations, John Gould realized all collected
  - each finch had a different beak to specialize in food types

Effects of Weather: #

during drought, food is scarce and only food is hard seeds
finches begin to adapt to have larger beaks
- those that already have big beaks more successful
decrease in variation in size

Evolution is not progress. #

Success is local and temporary; environments are constantly changing.

Behavioral Immunity

Mon, 01 Jan 0001 00:00:00 +0000

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Loss of Heterogeneity in Humans #

humans are very similar genetically
Population thinking: Crises lower population → smaller gene pool
- greater influence on founder effects
  - at some point in history, only 20,000 humans were alive

Impact of disease on human evolution #

Until WWII, more soldiers died of disease than wounds
Decimation of native population: 50% of Aztecs died of smallpox, 95% of Indigenous North American populations

Why did Europeans carry diseases, but others did not? → A: agriculture

The Startup Problem

Mon, 01 Jan 0001 00:00:00 +0000

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The Start-Up Problem #

We need cumulative culture to be successful. When/how did this accumulate in the first place?

“Crossing the rubicon”: once stealing knowledge from others was more efficient than learning it yourself, there was no turning back

2 pathways: #

Know-how (mechanical)
Sociality (brain cost/ability)

Terrestrial Primates: #

Since humans don’t use arms for swinging on trees, they are free to use for innovating new behavior.
Less safety from predators → incentive to increase group size, become diurnal

Know-How Pathway #

Terrestrial → Greater danger → Larger social groups → More opportunities to learn → More knowledge of tool-making → More social learning

Olfaction

Mon, 01 Jan 0001 00:00:00 +0000

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Olfaction #

Noses #

Why noses? #

3 hypotheses:

evolutionary artifact: result of neutral evolution, genetic drift
respiration: nose evolved to warm, humidify air (proposed in 1913, refuted 2016)
stereo olfaction: evolved to support enhanced, adapted movement + navigation
- leads to greater space use → larger brains

Using Olfaction #

Odors are objects
- elements (single), configurations (mix)
- source of directional information
odor mapping prevalent in highly visual species, incl. humans
olfaction before brain: olfactory system/bulb evolved before neocortex
hippocampus related to olfaction
- dolphins don’t have either

Stereo Olfaction #

more accurate mapping w/ two nostrils
related to antennae (wide to determine location accurately)
- also seen in hammerhead sharks, snakes’ bifurcated tongues
- Procellariiformes (tube nose birds) → navigation, prey detection

The Human Nose #

no other ape has a wing/pyramid-shape nose
- first appears in homo erectus
evolved in part from climate change:
- environment becomes drier, more open
- rise of cooperative hunting carnivores w/ olfactory pursuit
- endurance pursuit allowed humans to compete bipedally
- nose widened/narrow based on geographic location → increase/decrease in space use
  - (ex. Arctic noses very narrow, low need for space)
- agriculture → sedentary life → low space use
evolved as response to agriculture: increased pathogens, decreased space use
- 2 modes: navigational (1.5 mya), diagnostic (15k)

The Scent of Disease #

early physicians trained to detect odors correlated w/ disease
dogs can detect tuberculosis, cancer, low blood sugar, covid…

Human:

Tool Use, Taxonomy

Mon, 01 Jan 0001 00:00:00 +0000

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Culture and Tool Use #

Primary difference between humans / other species: tools are manufactured (use tools to make tools)

Language

Mon, 01 Jan 0001 00:00:00 +0000

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Language as an Evolutionary Process #

language evolves like organisms
- needs to be learned quickly/effectively, or else it will die out
- adapts to environment
  - example: in open plains, birds speak in short notes; in forest, birds speak in long notes due to degradation of signal due to winds in plains

Human Communication #

gestures (sign language, etc.) → efficient distance signaling in open plains
- used by indigenous North American Plains people w/ spatial grammar (location, movement, shape, orientation of palm)
- evolved cultural taboos for speaking: close female relatives after man’s death in Waripiri Aboriginals
vocals (grunts, whistles, etc.)
- whistle languages in mountain societies: short, high, freq. sounds carry further
  - Sylbo (Spanish Canary Island), Turkey, Mexico

Sonority #

The relative loudness of speech that is determined by how open the mouth is

Reproduction

Mon, 01 Jan 0001 00:00:00 +0000

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Babies #

Two types:

Altricial: born undeveloped #

long post-hatching period for brain to develop
competitive ecological niche that requires skill
low juvenile mortality

Precocial: #

born immediately able to move, eat, etc after birth
abundant, low-skill food (eg chickens)

K-selected species: fewer offspring with long-term care (K = limited by carrying capacity) R-selected species: lots of offspring that are not specialized (R = limited by reproductive rate)

Mating Systems

Mon, 01 Jan 0001 00:00:00 +0000

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Mating Systems #

Monogamy: 1 woman 1 man — rarest in humans
Polyandry: 1 woman multiple men — most common (mild polygyny)
Polygyny: multiple women 1 man
Polygynandry: multiple women, multiple men

Default system for humans: serial monogamy (can remarry) #

polygyny acceptable but uncommon
more wealthy (older, successful) men → more polygynous (more success for women vs. marrying poor)

Example: Kisigi pastoralists in Kenya #

forcibly moved by Europeans, studied marriages & land ownership
default polygyny, with some monogamy
as wealth increases, monogamous wives have lower reproductive success vs polygyny
- direct relationship b/tw acres owned, # of wives
- small # of successful males have most of the children (up to 80)

Variance in reproductive success #

Farmers > herders > hunter-gatherers (accumulation of material wealth ⇒ more inequality)

Religion

Mon, 01 Jan 0001 00:00:00 +0000

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Religion #

How did WEIRD evolve? #

Medieval Catholic Church #

In attempt to gain political power & wealth:

prohibited cousin marriage
created nuclear family system
destroyed pre-Christian non-WEIRD society (highly kin-based, arranged marriage, polygynous)
exposure to church ⇒ lower kinship intensity

Overall, universalizing religions created ethical codes, moral beliefs…

Purpose: to control wealth #

traditionally, marriages controlled power and formed alliances (strong kin network)
by restricting to male heir monogamy with no remarriage, very difficult to consolidate wealth.
- had to buy dispensations, annulments, bequests from church
  - if no heir, give all money to church when dying to guarantee good afterlife

Kinship Psychology #

Marriage and Family Program (MFP) #

Great Schism of 1054: Western Catholic Church split from Eastern Orthodox Church
due to dispersion and strict laws, very hard to officially marry

→ result: marriage between strangers, individual ownership, nuclear family away from kin ⇒ individualism

Power

Mon, 01 Jan 0001 00:00:00 +0000

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Dominance and Power #

Primate Origins #

Baboons: hierarchical power structure w/ alpha male
based on physical dominance (embodied wealth) — individually earned
female power inherited from matriline

Human Origins #

survival requires cooperative hunting + scavenging + breeding
decades of training required to maximize embodied wealth + knowledge ⇒ long lifespan
invention of weapons ⇒ evolve new form of dominance
- control of group by leader = dominance (evolved 7.2 mya in primates, 1.2 mya in humans)
- control of leader by group = reverse dominance (eg. voting)
- social control of deviants ⇒ invention of capital punishment
  - punishment often meted out by kin (transgressors are dangerous, but don’t want inter-family conflict)
- lethal weapons are a uniquely human invention
  - recent adaptations for projective weaponry: good aim, throwing power from homo erectus shoulder

Human Aggression #

Human aggression is unique — increased proactive aggression, reduced reactive

Patriarchy

Mon, 01 Jan 0001 00:00:00 +0000

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Patriarchy #

Humans have a uniquely unequal gender relationship #

Men historically had most power, and were able to keep it
Men particularly interested in controlling female sexuality and reproduction
Evolutionary success results from dual inheritance
Material wealth inequality drives male control

In leadership: #

Implicit bias — women judged as less competetive, independent (no evidence in practice of performance difference)
Female leaders are more egalitarian and democratic
- Women have more power in egalitarian societies (Chimani)
  - Major role in mediating conflict
- Increased wealth → increased gender equality

Male Aggression is Cultural #

Yanomamo (Amazonia): hunting society w/ lethal fighting
- Violent female coercion
- No paternal childcare
- Polygyny
Aké (West Africa): foraging society
- No male-female aggression
- Monogamy
- Highest levels of paternal care

— Evidence for dual inheritance theory: gender differences depend on culture

Norm Psychology

Mon, 01 Jan 0001 00:00:00 +0000

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Norm Psychology #

We live in a world with social rules (often arbitrary)
Others react negatively to violations
- inference: others care if we follow them
Norms allow for large societies

Norms are quickly learned #

example: new pandemic norms

Norms enforced by group #

depend on which group

Norms create reputation #

protection from others: get backing of group for following
norm enforcement punishes non-conforming members

The norms of cooperation #

Kin selection (Hamilton’s Rule rB > C)
Direct reciprocity among non-kin
- repeated acts of altruism between two known individuals
Indirect reciprocity
- cooperative behavior: public norm following will gain social capital ⇒ others will provide support in the future
- ⇒ reward generosity, altruistic punishment for violation
Strong Reciprocity

C observes A help B C helps B due to reputation

Gods

Mon, 01 Jan 0001 00:00:00 +0000

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Spirits for Norm Enforcement #

Mentawai society: Sikameinan water spirit enforces meat sharing norms
- punishments, illnesses for those who do not follow
  - need to hire expensive shaman to cure problem
  - rituals very common
- functionally equivalent to a god, but domain is far more limited
  - each spirit has a very specific role

Belief ⇄ Ritual (belief motivates ritual; ritual enforces belief)

War

Mon, 01 Jan 0001 00:00:00 +0000

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War #

First evidence: 15,000 – 8,000 years ago (agriculture)
- Not found in all societies: wealth → defense → segmentation → growth → full scale competition
Simple War: no chain of command (rituals, displays, combat)
Raid: ambush, large number of attackers, minimal risk
Complex War: armies, professional soldiers

Evolution of War #

Zapotec: 700 BC – 1521 AD #

First city in Mesoamerica: Monté Albán
Began as simple villages ⇒ cities in 1200 years
Full scale war b/tw communities
- Storable wealth
- Territorial expansion
- Domestication of corn

Village Life
- Nuclear families w/ houses, storage pits
- Defense: palisades
San José Phase
- 1000 people in city

Psych 124: The Evolution of Human Behavior on

Intro to Evolution

Intro to Evolution #

Evolution is History: #

The goal of studying evolution: #

How to study human behavior #

Culture and Evolution

Culture and Evolution #

Why are humans so successful? #

1. We ate all the big animals #

2. Only 1 species of great ape survived? #

-1. Not because of our intelligence #

3. Culture #

Dual-Inheritance Theory #

WEIRD

WEIRD #

Effects on Visual Perception and Thought #

Cumulative Culture

Cumulative Culture #

Why do humans have so much cumulative culture? #

Study: are humans smarter than apes? #

Results: humans have similar physical cognition, but much better social cognition. #

Criteria for Teaching #

Repertoire of Cultural Transmission Strategies #

Evolutionary Thought

Evolutionary Thought #

History of Evolutionary Thought #

Natural Selection: #

Darwin and Natural Selection #

Effects of Weather: #

Evolution is not progress. #

Behavioral Immunity

Loss of Heterogeneity in Humans #

Impact of disease on human evolution #

The Startup Problem

The Start-Up Problem #

2 pathways: #

Terrestrial Primates: #

Know-How Pathway #

Olfaction

Olfaction #

Noses #

Why noses? #

Using Olfaction #

Stereo Olfaction #

The Human Nose #

The Scent of Disease #

Tool Use, Taxonomy

Culture and Tool Use #

Language

Language as an Evolutionary Process #

Human Communication #

Sonority #

Reproduction

Babies #

Altricial: born undeveloped #

Precocial: #

Mating Systems

Mating Systems #

Default system for humans: serial monogamy (can remarry) #

Example: Kisigi pastoralists in Kenya #

Variance in reproductive success #

Religion

Religion #

How did WEIRD evolve? #

Medieval Catholic Church #

Purpose: to control wealth #

Kinship Psychology #

Marriage and Family Program (MFP) #

Power

Dominance and Power #

Primate Origins #

Human Origins #

Human Aggression #

Patriarchy

Patriarchy #

Humans have a uniquely unequal gender relationship #

In leadership: #

Male Aggression is Cultural #

Norm Psychology