• Genes in DNA are in charge of producing specific proteins needed to build a specific type of cell, like skin cell.
• Genes can be turned on and off.
  • When genes are turned on, they are free to produce the proteins.
• Genes are turned on not only during body development, but also because of environmental factors.
• Mice example:
  • when a pregnant mice consumes foods containing BPA - found in platic and other products - its child had yellow fur and obese.
  • BPA turned on the Agouti gene - a gene that produces yellow fur and obesity.
    • Reduced methylation of Agouti gene influenced obesity and yellow fur?
  • Diet rich in Choline, Betaine, or Vitamin B12 could turn off the Agouti genes.
• Mice example relates with human in that twins are likely to eat different foods and have different experiences, which affects DNA, which is why as they grow older they become different.

1. Why Do We Say That Nature and Nurture Are Intertwined?

• We are looking at how nature and nurture shapes our behavior.
  • Nature: Contributions of heredity to our physical structures and behaviors
  • Nurture: Contributions of environmental factors and experience to our physical structure and behaviors.
• Contemporary psychologists look at nature and nurture as being closely intertwined.
• Eariler scholars, however, thought of it as nature versus nurture.
  • Francis Galton (1869): first to use the phrase nature vs nurture.
  • Galton believed that intelligence is largely the result of inheritance.
  • He was a cousin of Charles Darwin (maybe we know why he thought that way..)
• By integrating a number of perspectives - both biological and experiential - we can achieve more accurate understandings of these questions.

2. What are the building blocks of behavior?

• Every nucleus except for red blood cells and sperm or eggs contains two complete copies of human genome, a set of instructions for building a human.
• Genotype: An individual's profile of alleles, or a personal set of instructions.
• Phenotype: An observable characteristic. Genotype interacts with environment to produce it.
• allele < genes (smaller segment of DNA) < DNA < chromosomes
  • Genotype is determined by genes.
  • Majority of our cells have 46 chromosomes (23 pairs), half contributed by mother and the other by father.
• Gene expression: the process in which genetic instructions are converted into a feature of a living cell.
• allele: different versions of gene
  • can give rise to different phenotypical traits.
  • an individual receives only two: one from each parent.
• Homozygous: Same alleles.
• Heterozygous: different alleles.
• Recessive & Dominant alleles:
  • Dominant: determines a phenotype in any condition.
  • Recessive: determines a phenotype only when homozygous.
  • Example 1: Freckle allele is dominant - one parent has it, the entire family has freckle.
  • Example 2: Serotonin transporter gene is either short (S) or long (L). It is recessive so SL genotype is midway between SS and LL in terms of emotional reaction to bullying.
    • LL reacts the least emotionally.

2-1. Genetic Variation

• During meiosis (reducing the number of chromosomes to 23, one from each pair), 2^23 of chromosome combination is possible.
• For child conception, the possibility should be 2^46.
• This explains why even siblings have different physical traits.

2-2. Relatedness

• Relatedness: the probability that two people share the same allele from a common ancestor.
• 1/2 chance I would share the same allele with my parent/sibling, 1/4 chance for grandparents or uncles, 1/8 for cousins.
  

2-3. Sex Chromosomes

• Male: XY, Female: XX.
• Hemophilia allele is effective to males:
  • Hemophilia allele is found only on the X chromosome
  • Females can offset the Xh chromosome with another X.
  • Males do not have extra X chromosome

3. Which fields of genetics are relevant to psychology?

• Humans share some genes with other spieces, but at the same time have different genes that set them apart.
  • FoxP2 has significant effect on human language
• Subfields of genetics that are relevant to psychology behavioral genetics, molecular genetics, functional genetics, and gene-environment:
  • Behavioral genetics attempts to discover the strengths of genetic influences on particular behavior,
  • Molecular geneticists look for candidate genes:
    • genes that have greater impact on a trait of interest than other genes.
  • Functional geneticists study the entire genome looking for whole patterns of genetic differences linked to a given trait.
  • Gene-environment geneticists look for situations in which candidate genes appear to have different effects.
    

3-1. Behavioral genetics and heritability

• Behavioral genetics investigates the strength of genetic influences on a particular behavior.
• Heritability is the statistical likelihood that variations in a trait observed across individuals in a population is due to genetics.
  • Heritability is usually computed by comparing monozygotic (identical) and dizygotic (fraternal) twin pairs,
  • reason is that if a certain trait is more similar between MZ twins than DZ twins, it is attributable to genetics.
• Shared experience and non-shared experience also contribute to a trait.

3-1-1. Confusions regarding heritability

• Heritability is a population-level measure. It never refers to an individual.
  • When the heritability of shyness is 40%:
    • a. means the variations in the levels of shyness within the studied population is 40% due to genetics.
    • b. does not mean that an individual's shyness is 40% due to genetics. Environment could have had more impact on that person's shyness.
• Heritability cannot be assessed without taking the environment into account.
  • If the environment is held constant, the heritability of a trait will appear to be high.
  • Example 1: Plants grown in same lighting and soil will have differences in growth purely due to genetic reasons.
  • Example 2: Adoptive families go through screening process which makes them similar to one another. This facilitates the study of differences between children and their adoptive/biological parents.

Extra:

• Concordance rate: statistical probability that a trait seen in one person will be seen in another.
  • Example: Concordance rate of autism is higher for identical twins than for fraternal twins.
    • Since both types of twins are raised in the same uterine environment and parenting, the difference of concordance rate can be attributed to genetics.

3-2. The Search for Candidate Genes

Motivation:

• The primary goal of psychology is the understanding and effective treatment of psychological disorder.
• Comparing variations of DNA can help psychologists pinpoint the causes of these problems and suggest preventive strategies.
• Before technologies were so advanced, investigating more than a few genes was impossible.

Candidate Genes:

• A gene that has a greater impact on a trait of interest than other genes.
• Molecular geneticists would choose a single or a small number of genes and compare between groups of people with and without a condition of interest.
• This can be rather challenging because we don't know what exactly we are looking for.

Genomewide Association Studies (GWAS)

• Functional geneticists now use emerging technologies to scan complete sets of DNA from many participants.
• More complete, more accurate.
• Example: Type A people have higher risk for severe COVID-19 with respiratory failure than Type O people.

Common Misconceptions:

• A gene does not directly cause an observable behavior.
• Scientists must fill in the gaps between a gene and an observable behavior.
• It is more accurate to say that genes contribute - along with many other factors - to the development and functioning of nervous system, which in turn generates observable behavior.
  

3-3. Epigenetics

• The study of gene-environment interaction in the production of phenotypes.
• Epi is a greek word for "above",
  • so epigenetics refers to the reversible development of traits by factors "above" the genes themselves that determine how genes perform.
• Epigenetic change influences gene expression by turning on or off genes after receiving signals from internal or external sources.
• The magnitude of epigenetic change depends on an organism's age: the younger, the more susceptible.
  • Example 1: Individuals who experienced traumatic events in their childhood may experience lifetime vulnerability to mental health problems.
  • Example 2: Malnutrition and stress experienced by pregnant women have the potential to influence the epigenetics of the fetus.
  • Example 3: rats that were licked frequently by their mothers were calmer when faced with stress later in life than rats that were licked infrequently.
• There are four processes of epigenetic changes: ribonucleic acid (RNA) changes, RNA editing, histone modification, and DNA methylation.

Histone Modification:

• Histones are protein structures around which your DNA is wound.
  
• When either the core or the tail of histone interacts with regulatory proteins, the expression of nearby segments of DNA can become more or less likely.

DNA Methylation:

• Occurs when a methyl group is added to the DNA molecule.
  • Methyl: One carbon atom bonded to three hydrogen atoms.
• This usually has the effect of turning genes off.

Extra: "The Warrior Gene" MAOA

• does low activity in warrior gene indicate antisocial behaviors? (Brunner et al., 1993)
• Very small effect sizes.. tho
• People who have not been maltreated in childhood:
  • Differences in MAOA level does not affect chances of convicting violent crimes.
• People who have been maltreated in childhood:
  • Lower MAOA activity people had higher chance of convicting violent crimes.

Extra: Passing on Fear

• Trained mice to fear acetophenone
• Chemicals smells like almonds + cherries
• When the mice was exposed to acetophenone, he experienced electric shock.
• The fathers were trained,
  • their offsprings were also afraid of the odor,
  • the grandchildren were also afraid.
• Is it possible to pass on fear?
  • Needs replication
  • Need to rule out other possibilites.
    • The offsprings could have learned it from their parents by their reactions.
  • Does it apply to other behaviors as well?

4. How does evolution occur?

Combining current understanding of genetics with the natural selection processes provides scientists with powerful hypotheses about the progression of species over time.

• Evolution: descent with modification from a common ancestor.
• Charles Darwin, in his Origin of Species, proposed that species evolve from one form to the next in an orderly manner.
  • Farmers developed animals and plants with desirable traits by mating particular individuals,
  • Strong oxens were bred by mating two strong oxens.
  • Farmers used artificial selection - human intentionally selecting specific individuals for desirable traits.
  • Darwin suggested that the pressure of survival and reproduction in the wild would act to change the frequency of alleles in subsequent generations, known as natural selection.
    • Alleles advantageous for survival and reproduction tend to become more common, while those disadvantageous may decrease in frequency or be eliminated.
• Darwin was unable to account for variations in observed traits.
  • Gregor Mendel (1822-1884) provided explanations to this through his study of ways to predict inheritance of particular traits, like the color of flowers, in his research on pea plants.

4-1. Mechanisms of Evolution

• In addition to natural selection, evolution can happen from mutation, migration, and genetic drift.
• Mutation: an error that occurs when DNA is replicated.
  • A new genetic variation is introduced by altering DNA sequences - happen by chance.
  • Mutant alleles that provide advantages spread through the population, while those disadvantageous disappear.
• Migration: Organisms move from one geographical location to another.
  • A certain phenotype that was effective in one environment may not in another,
  • then the changes in frequencies of alleles occur.
• Genetic Drift: Happen by chance or accident.
  • Example: Blood type B is absent in contemporary Native Americans because the none of the first arrivers to the Western hemisphere had type B blood.

4-1-1. Example with Blonde Hair

• Mutation:
  • The original appearance of blonde hair must have happened due to ramdom mutation.
• Migration:
  • The lack of migration made blonde hair indigenous to northern Europe.
• Genetic Drift:
  • Bubonic plague decimated European population, resulting in reduced blonde hair alleles from 1300-1700.
• Natural Selection:
  • If people are given choices between mates with equal values, they would choose the one that stands out more.
  • Most Germans are blonde.
  • German men find blonde women as good homemakers and dark hair women sexually attractive.

4-1-2. Fitness

• Fitness is the ability of one genotype to reproduce relative to other genotypes.
• It describes the interaction between characteristics and the environment in which they exist.
• The fittest are not simply strong or quick, but they have characteristics that allow them higher chances of survival.
  • Example: Animals in cold climates have short legs and stocky bodies to retain heat.
• This proves the need to consider both nature and nurture.

4-2. Adaptation

• refers to either the process or result of change because of natural selection.
• Species can respond to environmental changes, and the new phenotypes are called adaptations.
• English Peppered Moth shows a good example of adaptation:
  • Most EPM were light colored to hide behind tree barks - there were only few dark colored ones.
  • During Industrial Revolution, tree barks were coated with soots.
  • EPM adapted to this change by increasing the frequency of dark colored EPM.
  • As pollution came under better control, EPM again went back to their original light colored forms.
• Adaptations often are compromises between costs and benefits:
  • Men with higher testosterone report having more sex partners and earlier age at intercourse,
  • but they also have low immune system, more vulnerable to diseases.

4-3. Evolution of the Human Brain

• Nervous system is fairly recent innovations.
  • Origin of the Eart at 4.5 billion years ago,
  • First single-celled life form 1 billion years later,
  • First neural nets appeared only 700 million years ago,
  • Formed skeletons 500 million years ago,
  • First decidedly human brain 7 million years ago (hominin),
  • Current model of human brain 100,000 - 200,000 years ago.
• Hominin walked on two feet and had large brains.
• Brains grew rapidly, suggesting that improved intelligence contributed to higher chance of survivals.
  • Australopithecines: 400 cm^3
  • Homo erectus: 700 cm^3
  • Homo sapiens: 1300 cm^3
  • Brains were getting larger.
• The major distinguishment between humans and other species' intellgence is the richness and complexity of the social behavior.
  • distinguishing friends and foes,
  • imitate the behavior of others,
  • use language to communicate, ...

4-4. The Contemporary Human Brain

• How does our brain not get bigger anymore?
  • We have reached equilibrium between our needs for intelligence and the costs of a big brain.
  • Brains are expensive to run in terms of nutrients.
    • requires about 20% of body's resources.
  • Brain sizes may be limited by the dimensions of the birth canal.
  • unless we experience drop in the costs of big brains, a change in nutrients, or additional pressures for greater intelligence, bigger brains are unlikely.
• Average intelligence has not remained the same.
  • Environmental factors like health, nutrition, or education has increased or decreased average IQ scores.
    
    

5. How does evolution influence behavior?

• Behavior as a phenotype is considerably more complex than other physical traits like color of an eye.
• Darwin thought that behavior is shaped by the same evolutionary forces that affect physical traits.
  • "The difference in mind between men and the higher animals... certainly is one of degree and not of kind."

5-1. The Evolutionary Psychology Perspective

• The current topic relates with evolutionary psychology, a subspecialty of biological psychology that is a direct descent of Darwin's evolution and William James's functionalism.
  • Our current behavior exists in its present form because it provided some advantage in survival and reproduction to our ancestors.

5-2. Origins of Social Behavior

• Belonging to a social group provides mutual protection and assistance.
  • Predatory fish are most likely to hunt in the perimeter of a fish ball,
  • In other words, fish that are not in the center of a social group is exposed to danger, because it is easier to isolate them.
  • This is probably why we react so emotionally when we believe we are being socially excluded.
• There are disadvantages to being social, like fighting for foods and mates, but it seems advantages outweight the costs for many species.

• Both parties benefit if they cooperate.
  • two hunters may hunt together and share food.
  • much social behavior originated in these types of situations.
• One person wins and he makes others lose: selfishness
  • A person may steal foods from others.
• One person makes others lose by making himself lose: spite.

5-2-1. Altruism

• When one sacrifices to let others win, it is altruism:
  • Honey bees sting and die to protect their hives.
  • Emperor penguins make huddles with other parents to protect chicks from hostile Antarctic cold.
• Most challenging to explain:
  • "If altruism results in the destruction of the individual with altruistic genes, why doesn't this behavior disappear from the population?"
  • can be explained with relatives:
    • we could sacrifice our lives to save a close blood relatives to increase the likelihood of passing down our alleles to subsequent generations.
  • We would be altruistic to people other than our relatives in expectation that the person would return the favor in the future - reciprocal altruism.

5-3. Sexual Selection

• Darwin's term for development of traits that help an individual compete for mates.

5-3-1. Parental Investments

• Females bear most of reproduction, from giving birth to nurturing the young till childhood.
• Human females have more limitations than males on the number children.
• Promiscuity in males and abandoning their children does not guarantee survival of their offsprings.
• Females can make accurate predictions of man's interest in children:
  • Men with higher testosterone are viewed less likely to participate in childrearing than those with lower testosterone.

5-3-2. Traits possibly influenced by Sexual Selection

• Intrasexual selection:
  • Members of one sex compete with one another for access to other sex.
  • "Intra" because competition happens in one sex.
  • For deers features like larger antlers, which are beneficial for fights, could become easily selected.
• Intersexual selection:
  • Characteristics of one sex that attract the other might become sexually selected.
  • Male peacock's luxurious tail.
• Human traits might have been subjected to sexual selection:
  • Humor could be used to impress females.
  • More uncommon vocabs can be used in romantic relationships.
  • Risky behaviors should be avoided to attract females - though males' dominance over other males can be related with their involvement with risky endeavors.

5-4. Culture

• Genetics and evolution shaped brains, and brains form cultures.
• Cultures provide practices, values, and goals that can be shared by groups of people.
• Experiences shaped by culture interact with survival and reproductive pressures:
  • Yamamono: more aggressive, more offspring production.
  • Waorani: less aggressive, more surviving offsprings.
• Development of agriculture improved control of food supply, decreased geographical mobility, and made larger communities that led to a new era of social interactions.
  • Land ownership made patriarchal system where males inherit the lands,
  • This is contrasted with hunter-gatherers egalitarian society.
• With larger communities, humans used their brains to devise systems to maintain group cohesion.
  • Controlling marriage, "character" issues, and the transfer of precious resources are common themes across moral, religious, and legal systems of diverse cultures.
• Humans do not thrive alone.