Genetics and Heredity
•	The Blank Slate
•	How to study genetic influences
•	Gene-environment interactions
•	How genes work
Argument of The Blank Slate
•	Social scientists have ignored complexity of human behavior
•	Afraid of biology
•	Over-emphasis on environment
•	Three harmful metaphors
•	Ghost in the Machine
•	Noble Savage
•	Blank Slate
The Ghost in the Machine
•	Doctrine that mind is separate from body
•	And free from material cause
•	Genetics unimportant in creating mind
•	Unconstrained in transforming individuals and society/culture
•	However…
•	Mind is dependent on body
•	But this does not eliminate free will 
The Noble Savage
•	Humans are basically “good” or at least not “bad”
•	Anti-social features of behavior are due to corrupt culture
•	However…
•	The “bad” is as central to human nature as the “good”
•	Limitations on our abilities to control the “bad”
The “New Look” according to Pinker
•	Discarding old and outworn assumptions
•	New ways of relating biology and culture 
•	Cognitive sciences – science of the mind
•	Brain sciences
•	Genetics
•	Evolution
Cognitive Sciences I
•	Exciting and interdisciplinary 
•	Combination of psychology, neurobiology, linguistics, philosophy, and computer science
Cognitive Sciences II 
•	Computational theory of mind
•	Innate machinery of mind
•	Infinite possibilities of behavior and thought
•	Universal mental mechanisms can provide cultural and individual variation
•	Modular theory of mind
Computational Theory of Mind
•	Explaining the mind in terms of information flow
•	Information seen in terms of basic units similar to computer representations
•	Computer modeling and artificial intelligence
Innate machinery of mind
•	For mind to process information must be innate machinery
•	The rationalist argument
Infinite possibilities of thought and behavior 
•	Behavior not rigid 
•	Or deeply controlled
•	Because
•	We have vast store of information
•	And flexible machinery for combining
•	So combinations can be novel and creative 
Mental machinery and cultural universals
•	Language is best example
•	All languages obey certain universal rules
•	But the actual words spoken and surface grammars are different
•	Social behavior
•	All cultures facilitate and control sex and aggression
•	But surface rules differ
•	And so does behavior
Modular theory of mind
•	Will consider more generally with evolution
•	Basic argument is that there are universal modules of thinking
•	Cognitive skills
•	Little agreement on what or how manufactured
•	Can be combined differently
•	In different situations
•	And in different cultures

The doctrine of the Blank Slate I
•	Most controversial part of the book
•	Early 20th century social science
•	Responded to 19th century emphasis of race and heredity
•	Moral lessons from new science
•	Eugenics
•	Racial and gender inferiority
•	Emphasis on “bad” human nature 
•	Thomas Hobbes (1588-1679)
•	People are selfish and respond only to rewards and punishments
Enlightenment emphasis on perfectibility and progress
•	British Empiricism
•	No innate human nature
•	Importance of learning and environment
•	John Locke (1632-1704)
The doctrine of the Blank Slate II
•	Standard Social Science Model
•	Behaviorism
•	No innate human nature
•	Learning is crucial
•	Cultural determinism – Boas
•	Cultures are arbitrary but powerful
•	Shape behavior
•	Social constructionism – our sense of reality is entirely socially constructed
Problems
•	A lot is innate – Rationalism
•	Cultures are important 
•	But are not arbitrary
•	And themselves products of evolutionary forces
•	Some parts of reality are social constructions, but
•	There are real environments
•	Real genes that produce real people
Genetic determinism and the blank slate
•	Fear that emphasis on genes destroys free will
•	And removes moral responsibility
•	Reductionism
Do genes destroy free will
•	No more than environment’
•	Both are represented synaptically
•	And synapses don’t care
•	More generally the fact that thoughts and behaviors have neural correlates doesn’t prove anything about causality
•	Free will can still exist
•	Genes enable much as an operating system does on a computer
Do genes destroy moral responsibility
•	Naturalistic fallacy – an “is” doesn’t make a “right” (or “wrong”).
•	Individually and culturally we make decisions to override genetic pushes and pulls
•	And our genes also contribute to our moral sense
Reductionism
•	Bad reductionism seeks to reduce everything to simpler or earlier states
•	Often uninformative
•	And leaves out important interactions and combinations
•	Good reductionism 
•	Progress at different levels
•	How levels are related
Important points I
•	Genes control everything, but interact with environment to do so
•	Biology is not destiny 
•	Genes don’t parse behavior the way psychologists do – repeat
•	Naturalistic fallacy
Important points II
•	Heritability refers to explanations of variance within populations
•	Does not necessary explain group differences
•	Genetic effects still require explanation in terms of mechanism
•	The fallacy of single gene explanations
How we study genetic effects on human behavior
•	Extrapolation from animal studies
•	Much of the genome is common 
•	We share at least 98% of our genes with chimps who are actually closer to us than to gorillas
•	Gene altered mice and fruit flies
•	Correlational studies
•	Compare genes of people in various groups
•	Twin studies
•	Adoption studies
Macro genetics
•	Twin studies
•	Adoption studies
•	Nature vs. nurture
Comparing genes – correlational studies
•	Look at gene differences for known groups
•	Typically the group of interest and a control
•	Hard to specify relevant controls
•	Often find differences
•	Problems
•	Failures to replicate
•	Tricky research 
•	Often samples are from same family or location
•	Chopstick genes
•	Parsing, parsing, parsing
Twin studies
•	Monozygotic have identical heredity
•	Dizygotic share 50% (like all siblings) but have similar environments
•	Siblings have 50% genetic overlap but less similar environments
•	Unrelated children (adopted) have 0% overlap but have similar environment
Assumptions
•	V = H + Es + Eu
•	Note that this equation is additive
•	So no interactions
•	Meaning that heredity does not affect environment
•	Or visa versa
•	But rarely true
Environment and Heredity
Problems with assumptions
•	Hard to assess similarities in environment
•	Do DZ have similar environments than sibs?
•	Are MZ raised apart raised in dissimilar environments
•	Genetic-environment interactions
•	People with particular disposition may create a particular environment
•	Similar appearance and genetics may create similar environments
•	The case of body type
•	Aggression
•	Introversion/extroversion
Before birth confounding
•	MZ twins share uterine environment
•	Chorion environment
•	About 70% of MZ share placenta
•	MC share blood and maternal hormones
•	MC may also make them differ because of uneven blood supply or incompatibilities DC may make twins differ
•	But MC may inflate heredity – most studies find more concordance for MC-MZ
Results from twin studies
•	Usually find high concordance for MZ raised together
•	Slightly less for MZ raised apart
•	DZ and sibs virtually identical and lower than MZ
•	And unrelated essentially 0
Adoption studies
•	Almost always find higher correlations with biological than with adoptive parents
Genetic effects
•	Still most agree that genetics plays a major role
•	Affects most measured traits
•	Obviously appearance
•	Physical mannerisms
•	Abilities
•	Personality
•	Beliefs and attitudes
•	Preferences
Environmental effects
•	Many studies find few
•	Once genetic influences are partialled out
•	And shared environment
•	Has led some to conclude that family influences are unimportant
•	To be discussed later in course
Power of heredity vs. environment
•	Paradox of environmental equality
•	Environments may act in non-linear ways
•	Need some reasonable type of environment but beyond that doesn’t much matter
•	Individual differences in response to environment
•	Our measures of environment are quite crude and effects may be subtle
•	Single episode effects

Moreover environment can affect gene expression
•	Homosexuality – older brothers
•	Schizophrenia, depression, etc. 
•	Ring finger/index finger ratio – in utero
•	Marker for testosterone
•	Autism
•	Dyslexia
•	Homosexuality
•	Lighter babies more at risk for heart disease
•	Light weight turns on preservation genes
•	But later abundant diet strains heart
•	Cancer a disease of genes – environment
Important gene-environment interactions
•	Heredity may create environments
•	People select situations
•	Parents go with the flow
•	The reading example
•	Vulnerability genes
•	New Zealand study
•	Probably homosexuality, schizophrenia, etc.

The fallacy of single gene explanations
•	Few humans features are due to a single gene
•	Genes in combination
•	Genes at different points in development
Gene mechanisms
•	People have 23 pairs of chromosomes
•	Each containing a variable but matched set of genes
•	Except for the sex chromosome
•	Genes consist of sequences of DNA made up of three pairs of bases -- exons
•	There are 4 bases A, C, G, & T
•	Each of these triads is capable of producing an amino acid
•	Through the mediation of RNA
Exons vs. introns
•	DNA triads that specify proteins are called exons
•	Those that don’t are called introns
•	Often called junk DNA 
•	perhaps remnants of genes once useful
•	But now discarded
•	But may indirectly influence exons
•	Perhaps as much as 98% of the genome
Making proteins
•	Proteins are sequences of amino acids
•	There are 20 important amino acids but 64 (43) possible base triads
•	So a given amino acid can be “made” by different exons
•	For example an AGT might produce the same amino acid as GGG
•	Provides flexibility and redundancy
Proteins
•	May consist of several amino acids
•	May be or help produce
•	Hormones
•	Neurotransmitters
•	May turn on or off other genes
•	Or make new proteins by slicing and dicing other proteins
The function of genes
•	The Selfish Gene
•	Copy themselves
•	Make proteins
•	Hormones
•	Neurotransmitters
•	Developmental switches
•	Recipes for extracting information from the environment
•	Cosmides & Toby
The selfish gene
•	Genes compete for survival
•	And bodies are simply vehicles for achieving these goals
Obviously genes copy themselves
•	Every time a new cell is created
•	Because digital remarkably accurate
•	But errors maybe1 in 2 or 3 billion copies
•	And environmental insult – radiation
Genes as on-off
•	All cells (except red blood cells, sperm and eggs) contain the entire genome
•	Most genes in most cells not needed
•	So almost all switched off (or never switched on) in a given cell
•	Why important
•	And may be switched on and off at different times

Gene as developmental switches
•	Proteins made by genes sometimes switch other genes on and off
•	Most genes require several different promoters and enhancers
•	And some can be switched on by different sets of activators
•	Different genes in different parts of the body may respond differently to different activators
•	And depending on what other genes have been activated
Some genes have a single purpose
•	For example the SRY gene on the male Y chromosome does nothing but turn on another gene
•	This other gene then turns on other genes that make turn undifferentiated embryos into males
•	Sexual organs
•	brains
•	And this happens at a very precise time (11th day in mice) and for a very short period
Most genes are flexible
•	Can have quite different effects
•	Depending on when switched on or off
•	Timing in development
•	Part of sequence
•	What part of the body they are in
•	Which other genes are producing activator proteins
•	Thus it makes little sense to speak of a gene as having a single purpose
•	Solves the problem of our having only 30,000 genes
How can so few genes produce so much
•	Complexity of gene interactions just discussed – Pinker says the flow diagram is important
•	Same gene can produce many different proteins
•	Junk DNA (maybe as much as 95-98% of all DNA) doesn’t specify proteins 
•	But may influence the parts that do
The Fallacy of Single Gene Explanations
•	Almost nothing is caused by single genes
•	Misled by diseases
•	Even physical features are not
•	Human behavior caused by interactions
•	Genes with genes
•	Temporal interactions
•	Genes with environments

Genes are not blueprints
•	There is no one-to-one correspondence between genes and behavior
•	Why
•	Behaviors caused by multiple genes
•	Interactions with environments
•	Sequencing in development
Genes as recipes
•	Experience as ingredients
•	But without knowing how much and in what combinations no dinner
•	Genetic recipes then guide blending and combining of experiences
Genes as recipes for extracting information
•	Genes evolve because of particular environmental pressures
•	Likely that they are attuned to information in environment
•	Lead us to pay attention and respond to particular environmental cues
•	Will see this argument later
Limitations of genetic explanations
•	Genes code for proteins
•	Thousands work in human body
•	Little understanding of which proteins do what
•	Always need causal mechanisms
•	The case of violence
•	Or depression
•	The parsing problem – violence as example
•	Dangers with genetic fiddling