Genetics and Evolutionary Foundations of Behavior

genome

complete set of genetic material, “blueprint” for making and maintaining an organism

DNA

molecule that carries genetic information, organized and packaged within chromosomes

most human body cells carry 2 pairs of 23 chromosomes (46 total), except repoductive, carrying 23

gene

• segment of DNA that codes for a particular protein. humans ahve 2 versions (alleles) of each gene, 1 from each parent

• collectively, these 2 alleles make up the genotype for that genes

• eg if N = high neuroticism, n=low neuroticism, could have NN or nn (homozygous) or Nn (heterozygous)

phenotype

observable characteristics of an individual, produced by interaction of genotype and environment

recessive vs dominant gene determining phenotype

recessive alleles determine phenotype only when individual is homozygous for gene, whereas dominant alleles determine phenotype regardless. not all genes act in dominant/recessive fasion

what do genes do

code for proteins, contributing to physical structures and functions of body and brain

behavioural genetics

establishing the degree of heritability for a given trait

evolutionary psychology

why certain genetically-encoded behaviours and traits emerged

candidate gene studies what are they

compare individuals with the candidate gene with individuals without on a given trait or disorder. pick genes based on theory or what we know about phsyiological systems involved

candidate gene studies limitations

• typically correlational

• other factors like other genes cannot be ruled out

• underestimate biological complexity of multifaceted traits and behaviors

  • difficult to replicate (issue exacerbated by small sample sizes)

animal models: gene knockout

remove or deactivate gene

gene knowdown

make gene less active

then compare genetically modified animals with wild-type animals to see impact of gene on behaviour or trait

mice who don’t miss mom case study

OPRM1 gene codes for part of cells that receive signals from opioid drugs and body’s naturally produced opioids (mediates reward, addiction, pain relief), speculated to contribute to formation of attachment bonds and behaviour (love)

genetic knockdown of u-opioid receptor in mouse pups causes deficits in attachment (Oprm-/- emits fewer seperation distress calls relative to wild-type controls (Oprm+/=), and do not develop preference for mother’s olfactory cues (in contrast to wild-type controls)

GWAS studies

• genome-wide association studies

• instead of looking at single gene (or small set of genes), scan entire genome and look for associations with particular phenotype

• may allow us to identify variants missed through candidate gene approaches

GWAS limitations

• run risk of false positives

• biological relevance often not clear

• still correlational

genes shape environments

genes shape behavioural tendencies and preferences, and thus the environments you seek out

with correlational research, run risk of combining genetic and environmental factors

can combine candidate gene approaches with experimental studies (eg expose participants to lab stressor to impact of stress-related gene on physiological or subjective stress.

diathesis-stress model

some individuals have predisposition (diathesis) that makes them more vulnerable to negative environmental influences (eg stress)

differential susceptibility model

some individuals are more sensitive to both negative and positive environmental influences

phenotype

product of genotype and environmental influence

not all genes are being read all the time, environmental factors affect which genes are turned “on” and “off”

social experiments have significant impact on expression human genome example

chronic social isolation linked to widespread changes in genetic expression in immune cells (>200 genes showing >50% difference in avg expression levels)

• upregulation of genes responsible for inflammation (which help with wound healing)

• downregulation of genes responsible for anti-viral response

epigenetic change

type of change to structure of DNA that affects gene expression without altering the underlying dna sequence

factors tat affect whether a gene is “read” or not. reversible, but can have long-lasting effects

DNA Methylation

process by which a methyl group attaches to some parts in DNA (epigentic process)

does not alter the protein the gene will produce, but rather influences whether the gene will produce it at all

methylated genes are generally “shut off”

epigenetics and maternal love and rat mom LG example

natural occurrence: High LG rat moms spend a lot of time licking and grooming offspring. offsprng are less stress-reactive than babies of low-LG mothers

not due to different genetic profiles. cross-fostering rat pups of low-LG moms produces behavioural profile associated with adoptive high-LG mother. these pups become high LG moms too (example of behavioural transmission of individual differences across generations)

exposure to high LG mothering leads to demethylation in area of glucocorticoid receptor gene in hippocampus, which is negative feedback for physiological stress response.

demethylation → greater expression of glucocorticoid receptors in hippocampus → more negative feedback → lower circulating glucocorticoid levels

established causality of effect by administering drug that promotes demethylation (used drug that makes pups

may be adaptive in dangerous, resource-scare environments. promotes vigilance for threat, stuff. proof: maternal stress during gestation leads to low LG behaviour in previously high-LG moms

early life adversity in brain through epigenetic processes example

victims of childhood abuse: had higher demethylation of glucocorticoid receptor gene in hippocampus (does negative feedback for physiological stress response)

established causality of effect by administering drug that promotes demethylation. drug made pups of LG moms resemble babies of high LG moms

behavioural genetics

study of strength of genetic influences on a behaviour/trait

heritability

how much of variation in phenotype across people can be attributed to variation in genotype (how much of an impact genes have on traits). applies to populations, not individuals, ranges 0-1, typical range is 0.3-0.6

family studies of heritability

twins closely genetically related should be more similar on trait than those who are not. problem: twins usually share similar environments

can compare identical/monozygotic twins (100% shared DNA) against fraternal/dizygotic twins (50% shared dna). examining variation in genes while holding environment somewhat stable

also can examine identical twins reared apart

twins studies assumptions and issues

MZ twins are treated more similarly, get adopted into more similar environments.

environment affects heritability estimates

heritability estimates higher in uniform environments. example: study of heritability of verbal IQ in children: overall heritability estimate: .57 but high parental education group: 0.74, but low parental education group (variety of other sources): 0.26

three key components to process of natural selection

1. variation

2. heredity

3. differential fitness

two sources of genetic variability

1. reshuffling of genes during sexual reproduction

2. mutations = errors during DNA replication

differential fitness

not all individuals in a population survive and reproduce equally. adaptations and survival of the “fittest”

functionalist approach

explains behavioural/mental/emotional/physiological processes by utility.

distal explanations (distant)

what role did behaviour play in survival and reproduction over evolutionary time (eg. male songbirds sing in spring to attract females/warn other males

proximate explanations

immediate triggers of behaviour (eg. increased daylight in spring triggers testosterone production which acts on brain regions responsible for singing

limitations of evolutionary explanations for behaviour

• cant go back to observe

• common behaviour =/= adaptive behaviour

• some traits are side effects of natural selection for other traits

• some traits from chance

• culture and environment

• justification of harmful social behaviour or inequalities

people naturally gravitate towards

small primary groups

people experience profound distress when their relationships are

threatened or lost

people quickly develop affinity even for what kinds of groups

meaningless

cross species universality of the need to belong: baboons

female baboons with stronger and more stable social bonds live longer, and better chances of their offspring surviving