Genetics and Heredity
•	What genes are
•	Macro genetic studies
•	Heritability and environment
•	How genes work
•	Freedom, ethics, and reductionism
Important points
•	Genes control everything, but interact with environment to do so
•	Biology is not destiny 
•	Genes don’t parse behavior the way psychologists do -- repeat
•	Habitability 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
What Genes Are
•	Much more than agents of heredity
•	Present in every cell
•	Function as “brains” of the cell
•	“Decide” nature of cell
•	And it’s function
•	All diseases are genetic diseases
•	And all behavior is genetic in origin
•	But interactions with environment
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
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
Uterine Environment
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
IQ Similarities by Relationship
Adoption studies
•	Almost always find higher correlations with biological than with adoptive parents
•	Independently of how close the two families are in measured variables
Still need a mechanism
•	People with higher IQs have larger brains
•	Especially gray matter
•	More densely packed neurons
•	Many studies find IQ correlated with RT
•	Especially in harder tasks
Genetic effects
•	Most agree that genetics plays a major role
•	Affects most measured traits
•	Obviously appearance
•	Physical mannerisms
•	Abilities
•	Personality
•	Beliefs and attitudes
•	Preferences
Schizophrenia
•	Base-rate of 1%
•	Cousin raises incidence to 2%
•	Half-sibling to 6%
•	Full sibling to 9%
•	DZ twin 16%
•	Both parents 40%
•	MZ twin 50%
What Heritability Means
•	Heritability is high for most features
•	Does not imply group differences are inherited
•	Or that the features of an individual can be said to be x% hereditary
•	The rectangles analogy. 
Rectangles
What else
•	Environment plays some role
•	But what and how?
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
•	Carol Harris
Power of heredity vs. environment
•	Habitability only assessed within specific environment
•	Relative strengths important
•	Paradox of environmental equality
•	Environments may act in non-linear ways
•	Need some reasonable type of environment but beyond that doesn’t much matter
•	Often find that heredity matters most for enriched environments
•	Individual differences in response to environment
Heredity may create environments
•	People select situations
•	Parents go with the flow
•	The reading example
•	Heredity becomes more important with age and shared environment less
Environments
•	Our measures of environment are quite crude
•	Single episode effects
Moreover environment can affect gene expression
•	Blanchard’s studies of homosexuality – older brothers
•	Ring finger/index finger ratio
•	Marker for testosterone
•	Autism
•	Dyslexia
•	Homosexuality
•	And created in utero
•	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
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 or bits of DNA
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
•	Virtually every cell contains the entire genome
•	Most genes in most cells not needed
•	So almost all switched off (or never switched on) in a given cell
•	And may be switched on and off at different times
Gene as developmental switches
•	All cells (except red blood cells, sperm and eggs) contain the entire genome
•	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
HOX Genes as Example
•	Some make vertebrae
•	Ones in snakes turned on for longer so have many
•	Whereas those in mice have fewer
•	HOX gene on longer for snakes
•	Same gene active in different places at different times
•	Timing and time of expression crucial

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
The case of Testosterone
•	Produced during gestation to determine gender
•	Then again at puberty
•	Secondary sexual characteristics
•	Body shape and for later (fat distribution)
•	Affects brain organization
•	Throughout life
•	Affects dominance behavior
•	Sexual behavior
How can so few genes produce so much
•	Complexity of gene interactions just discussed – 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
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
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