How culture transformed human evolution

• The human puzzle

• Culture allows rapid cumulative adaptation

• Culture leads to maladaptive behavior

How culture transformed human evolution

• The human puzzle

• Culture allows rapid cumulative adaptation

• Culture leads to maladaptive behavior

Humans are better at adapting to a wide range of environments than other creatures

Our ancestors were like contemporary apes

• Limited ranges

• Limited use of tools

• Small social groups

• Little variation

Humans are very different from other animals

• Range = whole world

Humans are very different from other animals

• Ranges whole world

• Complex tools crucial for survival

• Large social groups

• Extensive variation in Subsistence

Social arrangements

Exceptional ability to adapt to local conditions

Much human behavior is maladaptive

• False beliefs

Much human behavior is maladaptive

• False beliefs

• Dangerous hobbies

Much human behavior is maladaptive

• False beliefs

• Dangerous hobbies

• Reduced fertility

Much human behavior is maladaptive

• Dangerous hobbies

• False beliefs

• Reduced fertility

• Self-sacrificial altruism

• Not rare mistakes, but systematic deviations

The human puzzle…

• Humans are products of evolution,

• but…

• Humans are very different from other animals Tremendous ecological success, but.. do lots of wacky things

• How can we understand these facts in Darwinian terms?

The usual answer: Yogi & Alley Oop

• People are successful because we are so smart

• People behave maladaptively because our minds are adapted to Pleistocene foraging conditions

How culture transformed human evolution

• The human puzzle

• Culture allows rapid cumulative adaptation

• Culture leads to maladaptive behavior

People are able to adapt because they are so smart

These inferences are played out internally in mental models of the world, governed by intuitive conceptions of physics, biology, and psychology, including the psychology of animals. It allows humans to invent tools, traps, and weapons, to extract poisons and drugs from other animals and plants….

These cognitive stratagems are devised on the fly in endless combination suitable to the local ecology. They arise by mental design, and are deployed, tested, and fine‐tuned by feedback in the lifetimes of individuals…

Steve Pinker, “The cognitive niche”, PNAS in press

Intelligence alone is not the answer

• Your task is to survive on King William Island in the central Canadian arctic

You get year of supplies

Then, I take away all industrialized products.

Will you make it??

• I don’t like your chances...

• Franklin and McClure expeditions starved here

Inuit flourished where explorers died

• Key: adaptive, culturally transmitted information.

Subsistence skills Specialized technology Extensive knowledge of

arctic. Social organization

Culturally evolved adaptations allowed Inuit to flourish

Learning is subject to a generality-accuracy trade-off

• Specialized mechanisms allow complex adaptations to particular problems

• General mechanisms allow simpler adaptations to wider range of environments

Individual learning alone doesn’t usually lead to complex habitat-specific adaptations

Only humans have much cumulative cultural evolution

• Many examples of social traditions Norway rat pups acquire preference for

food they taste in mother’s milk Chimpanzees learn termite fishing

technique from mother

• Cumulative cultural evolution is rare Most traditions limited to behaviors in

animals normal repertoire Only bird song cumulates

Culture finesses accuracy-generality tradeoff

• Culture allows selective learning Learning situations vary Rely on learning when it is accurate or cheap, otherwise imitate

• Culture allows accumulation of small improvements Big improvements harder than small ones Accumulation of many small improvements can lead to complex

adaptations without specialized mechanisms

• Human populations accumulate adaptive information over generations that no individual could invent on their own

Culture allows the evolution of complex adaptations that individuals cannot invent

Copper Inuit bow

Culture allows the evolution of complex adaptations that individuals cannot invent

• Bow is an adaptation ≡ a complex object superbly designed for a task

• Bow played an crucial role in Copper Inuit subsistence• Necessary for caribou hunting in

late summer

• Provides food until sea freezes

• Hides/furs for clothing

• Show design features fit the task

Longer bows store more energy for a given draw

• Area under curve = energy stored

• Higher string angle lower force/draw

For a given draw weight, longer bows store more energy

• Allows higher velocity or heavier arrow

• Needed for hunting caribou & polar bear from a distance

Inuit made short but powerful bows

• Cooper Inuit didn’t have access necessary wood to make long bow Softwood drift wood Horn

• Had to splice smaller pieces

• Design features of Inuit short bows allowed them to be powerful Shape: wide, thin & tapered Cable-backed Recurved

Short powerful bows are wide, thin & tapered

• Wider bows are more powerful

• Wide bows must be relatively thinner Back is in tension, belly in compression Thicker bows experience more strain Shorter bows have higher radius of

curvature Shorter bows must be thinner

• Short bows should be tapered Most energy stored near handle Thinner tips lower mass Higher arrow speed.

Recurved bows are more powerful, but more strained

straight recurved

Initial string angle

Strained bows can be strengthened by sinew backing

Mandan Bow Pitt River CA Tejon CA

• Sinew backed bow has sinew glued to back of bow Sinew strong in tension Wood back less stressed Requires high quality animal glues Widely used in N. America, Asia

Shorter bows can be strengthened by sinew backing

• Sinew backed bow has sinew glued to back of bow Sinew strong in tension Wood back less stressed Requires high quality animal glues Widely used in N. America, Asia

• Cable backed bow has braided sinew line lashed to back of bow Glues hard to use in cold Animal glues fail in wet

environments

Mandan Bow

Cordage backed bowYukon DeltaMason 1893

Cable backed bow From Yukon delta

Short, flat, tapered bow

Cable-backed

Recurved

A Copper Inuit bow

Cordage made from twisted plies of spliced, twisted sinew

• Sinew provides the best natural fiber in most environments

• Problem: Sinew fibers are too short

• Solution: twist fibers to increase friction at splices

• Problem: How to keep fiber from untwisting?

• Solution: use two plys with opposite twist

Complex cultural adaptations key to human success

Polar Inuit lost much technology

• Polar Inuit isolated from other Inuit populations

• Elisha Kane winters with Polar Inuit during 1850’s

• Lacked many typical Inuit technologies Long entrance to snow houses Bow and arrow Leister Kayaks

• Lost technologies during a plague which spared only the young

Polar Inuit

Elisha Kane

Not able to reinvent it in 40 years

Merqusaq

• Rasmussen visits Polar Inuit in 1905

• Merqusaq tells of journey from Baffin Is to Greenland 40 years before

• Taught Polar Inuit how to make and use lost technologies

• Evidence it was useful Early Polar Inuit kayaks resemble Baffin

Island type, not West Greenland Hunted caribou with bows, seals from

kayaks Population decline reversed.

Polar Inuit

How culture transformed human evolution

• The human puzzle

• Culture allows rapid cumulative adaptation

• Culture leads to maladaptive behavior

Expect learned behavior to be adaptive

• The brain is a complex adaptation shaped by evolutionary processes

• People learn some things more readily than others

• Result: behavior that would have been adaptive in previous environments• Easier to learn fear of snakes than automobiles

• People prefer to raise their own children

• Brother-sister marriage is rare

• Controversial for humans, but standard assumption for other animals

“The epigenetic rules will then tend to channel cognitive development toward certain culturgens as opposed to others…Genetic natural selection operates in such a way as to keep culture on a leash.”

Lumsden and Wilson 1981: 13

Do genes hold culture on a leash?

Adaptation always constrained by tradeoffs

• E. g. No large flying animals.

• Reason: biomechanical tradeoffs

Cultural adaptation creates a tradeoff

• Benefit: low cost information.

• But, have to be credulous…

• Result: Maladaptive ideas can spread

Repeated transmission can amplify weak content biases

• Transmission chain experiments (Beppo & Griffiths 2008) Initial population trained on 50 data pairs Then given 50 values for argument, asked to estimate function Each subsequent generation trained on estimates of previous

generation

Generation 1 Generation 2 Generation 3 Generation 4

Prestige bias can lead to maladaptive runaway processes

• Imitating successful good general rule

• Number of other imitators a cue of success

• Imitate the prestigious a good rule

• But can lead to sexual selection-like runaway process

St. Simeonthe “stylite”

Rapid cultural evolution can increase variation among groups

• Repeated interaction and conformism lead to many behavioral equilibria

• Cultural adaptation much more rapid than genetic adaptation

• Culture can amplify variation among groups

Bell et al PNAS 2009

Maladaptation a consequence of cultural adaptation

• Evolutionary Psychology™: maladaptations due to novel environments

• The argument here: Maladaptations due to trade-off imposed by cultural adaptation

• Test: Did the same maladaptations we see now exist in Pleistocene foraging societies? Supernatural beliefs? Exaggerated prestige systems? Large scale social cooperation?

Man Thought of His Kayak, Irene Avaalaaqiaq, 1976

Complex cultural adaptations key to human success