Evidence for Learning Recall T0 T1 Success Biased
Evidence for Learning
Recall T=0 T=1 Success Biased imitation: More successful individuals more likely to be imitated than less successful individuals.
T=0 T=1 Reinforcement Learning: More successful behaviors held more tenaciously than less successful behaviors. Key common assumption: more successful becomes more frequent
Leads to optimal behavior: T=0 T=1 T=2 T=3
We will use to justify why our behavior is consistent with Nash (and hence our corresponding beliefs/preferences will have many of the counterintuitive properties of Nash, which we willmutate use to explain our puzzles) Some individuals H Row H Player H H H D D D Column D Player D H D D D D H H H D H U H D D D
We will show… 1) Evidence for reinforcement learning and success biased imitation 2) Even ideologies/preferences are influenced by RL & SBI 3) Functional behaviors can result 4) Even if we are not consciously aware of function+our purported justifications are fallacious. Note: won’t be “interdependent” yet; game theory won’t yet be used…just providing evidence for our premises.
First, let’s review the evidence for RL, and argue show it’s ubiquitous, powerful, deeply ingrained, and well designed to lead to functional behaviors.
BF Skinner shapes behavior in a pigeon
Can yield fairly adaptive behavior… Pretty nuanced system to enable optimal learning…
Now a bit of evidence for success-biased imitation… We will review evidence, more likely to imitate: -those who have shown success or knowledge, especially within domain, even in indiginous population -those who haven’t shown incompetent, even among infants -those who others are attending to (cue that they are doing stuff right), extends to preferences -especially imitate those who are most payoff similar: cohort, sex, ethnicity, language
More likely to imitate those who are successful, especially within same domain
Chudek et al (2011) show that 5 year olds More likely to imitate “prestigious” (succesful more likely to be prestigious)
Step 1: Show subjects video of “prestigious” model getting attention, and another getting ignored Step 2: Show both models expressing preferences over food, artifact, beverage, etc. Step 3: Elicit subjects’ preferences over these categories
More evidence… Also in other primates Studies of workers show that people disproportionately look at the most powerful person in the room and imitate how they sit And, obviously, advertisers regularly exploit prestige-biased imitation
And we are more likely to imitate those who are most likely to share same payoffs (sex, age, ethnicity…)
We showed: reinforcement learning/success biased imitation are powerful parts of human nature. Next we will argue: 1) Social learning is able to lead to functional adaptations -even some that are sufficiently complex that no indiv could figure out -even some that are as complex as biological evolution creates -even some that none of the people in the culture understand -powerful enough force that shapes biological evolution -much of our technological innovations w/o causal understanding 2) In fact, we have evolved specifically to learn even when opaque -over-imitation -if we only do what understand, we fail. -often mediated by ideologies or tastes 3) We will use this to argue: -social learning can get to Nash -even w/o anyone realizing, and in fact, will often come up with “logical” justifications (e. g. moral philosophy) -or will just “feel right” (e. g. moral emotions).
We learn beliefs/ideologies/opinions from prestigious, even if prestigeis in irrelevent domain
Built up a lot of useful cultural knowledge… How to build an igloo And when you lack such cultural knowledge: “ 1845…Franklin…two field-tested, re-enforced ice breaking ships equipped with state of the art steam engines, retractable screw propellers, and detachable rudders. With cork insulation, coal-fired internal heating, desalinators, five years of provisions including tens of thousands of cans of food (canning was a new technology), and a 1, 200 volume library” stranded on king William island cannibalism all died “…King William Island lies at the heart of Netsilik territory, an Inuit population that spent its winters out on the pack ice, and their summers on the island, just like Franklin’s men. “ Knowledge we can’t figure out individually, no matter what our incentives or resources…
What are the steps in an igloo? Do the Inuit “understand” these steps?
How is top panel different from bottom panel? Cultural Evolution can create complex adaptations just as well as Biological Evolution
Social learning so powerful…here is a list of ways it has shaped our biology:
“One morning in 1998, when I was living in rural southern Chile and working with the indigenous Mapuche, I arrived at my friend Fonso’s farmhouse to find him preparing what he called mote, a traditional Mapuche corn dish. He showed me how you have to scoop fresh ash out of the wood stove and put it into the corn mix for soaking, before heating it. ” Why do they put ash in their corn?
“…A diet based on corn can leave one short on niacin (vitamin B 3). Failure to get enough niacin results in a disease called pellagra, a horrible condition characterized by diarrhea, lesions, hair loss, tongue inflammation, insomnia, dementia and then death” “…To release this niacin, populations throughout the New World culturally evolved practices that introduced an alkali (a base) into their corn preparations. In some places, the alkali came from burning seashells (generating calcium hydroxide) or the ash of certain kinds of wood. Elsewhere, there were natural sources of lye (providing potassium hydroxide). Mixing the alkali into the recipe in the right way chemically releases the otherwise unavailable niacin in the corn”
Do you think the Mapuche understood this? “I thought that was curious, so I asked him why he mixed the wood ash in with the corn. His answer was “it’s our custom. ” Conclusion: Social learning can lead to highly functional behavior noone in the community “understands. ”
We evolved to imitate even when seems unessential(overimitation). (Unless there is an obvious explanation why they had to) Why?
Allows us to take advantage of socially involved adaptations that we don’t understand! Here’s what happens when we only imitate what we understand: “…By 1735, some populations in Italy and Spain had already become reliant on cornmeal, as a staple, and pellagra had emerged. The condition was theorized to be a form of leprosy, or somehow caused by spoiled corn …experiments were done, and laws were passed to address the problem, by prohibiting the sale of spoiled or moldy corn. This did little to reduce pellagra “
And now for some evidence that our beliefs and preferences can be socially learned (leading us to behave adaptively, even without our realizing the function)
Fijian Foods not eaten by pregnant women Why not?
Consensus grouping are most likely to carry Ciguatera, a dangerous toxin
Poisoning falls during pregnancy, (when immune system compromised, and fetus at risk) Are Fijians aware?
When asked why: “it is our custom” “babies would be born with rough skin if eat shark, or smelly joints if eat eel” “Gods will smite me” Notice: when learn stuff don’t understand, often come up with (fallacious) ideological jsutications (that lead to functional behavior) Aside: how different is this from Kant? Aside: how might this yield behaviors that are different from when understand?
Consistent with social learning model: Fijian women are not learning from their own experience, but from, those who are (close), older, successful, knowledgeable, prestigious (not direct experience!)
Why do we (especially Latin+Native Americans) like chili peppers? -Capsaicin directly activates Trp. V 1 pain channel in mammales, causing a burning senation, like acid and allyl isothiocyanate (mustard, wasabi) -innately repellent to mammals not birds, birds disperse better -in some societies capsicum even put on mothers’ breasts to initiate weaning
Spiciness People’s preferences for spices varies from location to location Source: Billing and Sherman 1998 and 1999 Why?
Spices are used most where they are most useful
(Also… dishes with meat usually spicier than vegetarian dishes)
What’s the mechanism? Change in taste! -desensitize to pain -learn to enjoy the pain receptor stimulation
Notice: we don’t just eat spicier foods when raised in hotter climates, we LIKE spicier foods. What difference does that make?
Notice difference between functional behavior being consciously chosen and functional behaviors resulting from learning/evolution of ideologies/preferences: -if I move from India to U. S. late in life, will I like spicy food? -Will I be able to tell you why I like spicy food? -Will it help us understand spicy food to model optimization given preferences?
To put in perspective: Ideologies that cause optimal behavior will also spread (even if not aware of function, and justification proffered is fallacious): S S S=love spicy food (will be reinforced in climate with a lot of parasites, bc don’t get sick) S S S S S=don’t eat Shellfish while pregnant, “b/c god will smite you” S S
Next Classes: -How much are our ideologies influenced by incentives? As compared to valid logic, evidence? -Some more discussion of proximate/ultimate distinction. Then: introduce game theory
- Slides: 47