Module 7 for psych
Behavioral Genetics and the Human Genome
Universal Human Behavioral Tendencies:
Shared brain architecture predisposes universal human behavioral patterns and tendencies regardless of geographical location (e.g., Arctic vs. Tropics).
Identical biological mechanisms govern sensory perception, language development, and hunger.
Universal preferences exist across cultures, such as preferring sweet tastes over sour tastes, dividing the color spectrum into similar categories, and engaging in behaviors that produce and protect offspring.
Shared social behaviors emerge universally regardless of surname or lineage (e.g., Gonzales, Lycomo, Smith, Wong):
Infants develop fear of strangers at approximately months of age.
Adults display a strong preference for the company of individuals with similar attitudes and attributes.
Universal species behaviors include affiliating, conforming, returning favors, punishing offenses, organizing status hierarchies, and grieving the death of a child.
Every human society engages in dancing, feasting, singing, worshipping, playing sports/games, laughing, crying, living in families, and forming social groups.
Individual Diversity and Core Definitions:
Environment: Every non-genetic influence, ranging from prenatal nutrition while in the womb to social support while nearing the tomb.
Heredity: The genetic transfer of characteristics from parents to offspring.
Behavioral Genetics: The study of the relative power and limits of genetic and environmental influences on behavior.
Cellular and Genetic Structure:
Every cell nucleus contains a genetic master code. Analogy: It is as if every room in Dubai's Burj Khalifa contained a book detailing the architect's full master plan.
The genetic code is organized into chapters called chromosomes ( donated by the mother's egg, and donated by the father's sperm).
Chromosome: A threadlike structure made of DNA molecules that contain the genes.
DNA (Deoxyribonucleic Acid): A complex molecule containing the genetic information that makes up the chromosomes.
Genes: The biochemical units of heredity that make up the chromosomes; small segments of giant DNA molecules capable of synthesizing proteins.
Humans possess approximately genes, which exist as either active (expressed) or inactive.
Environmental events turn on genes, similar to hot water enabling a tea bag to express its flavor. When activated, genes provide the code for creating protein molecules, which serve as the body's structural building blocks.
Genome: The complete instructions for making an organism, consisting of all the genetic material in that organism's chromosomes.
Polygenic Traits and Variation:
Genetically, every human is nearly an identical twin to every other human, sharing a common human genome that distinguishes humans from tulips, bananas, or chimpanzees.
According to behavioral geneticist Katherine Page Hardin, each pair of human parents could produce over () unique offspring, making individual trait combinations highly unique.
Most human psychological and physical traits are polygenic—influenced by many genes that each exert a small individual effect.
No single gene predicts complex outcomes like intelligence, sexual orientation, or personality:
A gene analysis of over individuals identified distinct genes associated with schizophrenia.
A study of individuals identified gene variations that collectively predicted approximately of the variance in people's total years of schooling.
Twin and Adoption Studies
Controlled Methodologies:
Ideal behavioral genetic experiments would either control heredity while varying the home environment, or control the home environment while varying heredity.
Though ethical constraints prevent performing such experiments on human infants, natural occurrences (twin births and adoptions) provide equivalent empirical conditions.
Identical vs. Fraternal Twins:
Identical (Monozygotic) Twins: Individuals who develop from a single fertilized egg that split in two, creating two genetically identical organisms. They share the same genes, conception, uterus, and usually birth date.
Fraternal (Dizygotic) Twins: Individuals who develop from separate fertilized eggs. They are genetically no closer than ordinary siblings, sharing on average of their genes, but they share a prenatal environment.
Diagnostic Risks:
If an identical twin is diagnosed with autism spectrum disorder, the co-twin has approximately a () risk of receiving the same diagnosis.
If a fraternal twin is diagnosed with autism spectrum disorder, the co-twin has approximately a () risk.
Researchers across medicine and psychology have studied nearly identical and fraternal twin pairs.
Identical twins display significantly higher similarity than fraternal twins in personality, emotional traits, political views, and even cannabis use habits.
Identical twins look so similar that most have difficulty distinguishing a flash photograph of their own face from their co-twin's face.
Control for Social Treatment: Researcher Nancy Siegel compared personality similarity between identical twins and unrelated look-alike pairs. Only identical twins exhibited similar personalities. Furthermore, identical twins whose parents dressed them identically were no more psychologically alike than identical twins dressed differently, proving that identical genes matter far more than identical treatment.
Separated Twin Studies & Case Studies:
Psychologists Thomas Bouchard and Nancy Siegel tested identical twins separated at birth and raised in distinct environments, finding remarkable similarities in taste, physical attributes, personality, abilities, attitudes, interests, and fears.
The Bogota Brothers Case (2015):
In in Bogota, Colombia, William Velasco (a butcher raised in a rural village) was mistaken by customer Laura Vega Garzon for her city-raised colleague, Jorge.
A hospital error at birth had swapped two pairs of identical twins: William was sent home with Wilbert (believed to be fraternal twins), and Jorge was sent home with Carlos (believed to be fraternal twins).
In reality, William and Jorge were identical twins, while Wilbert and Carlos were identical twins.
Genetic Similarities: William and Jorge were both strong, supportive jokesters. Wilbert and Carlos were both moody, serious, highly organized, prone to crying, and shared an identical speech impediment.
Environmental Divergences: City-raised Jorge and Carlos received better nutrition and grew taller than rural-raised William and Wilbert. Carlos received professional speech therapy while Wilbert did not, resulting in Wilbert being the only one of the two who struggled with speaking as an adult.
Criticisms of Twin Studies: Critics argue that coincidental similarities occur naturally if any two strangers of similar age, sex, and ethnicity compare life details ("the pearl of anecdote is not data"), that adoption agencies place twins in similar socioeconomic homes, and that many separated twins reunited years before personality testing. Twin researchers counter that separated fraternal twins do not exhibit the striking similarities found in separated identical twins.
Biological versus Adoptive Relatives and Gene-Environment Interaction
Biological versus Environmental Relatives:
Adoption sets up two distinct comparison groups: genetic relatives (biological parents and siblings) and environmental relatives (adoptive parents and siblings).
Core Personality Finding: Studies of hundreds of adoptive families show that, apart from identical twins, people who grow up together (whether biologically related or not) do not much resemble one another in personality traits such as extraversion and agreeableness.
Adopted children's personalities resemble their biological parents much more than their caregiving adoptive parents.
Except in extreme environments (such as conditions of war or famine), shared family home environment has no discernible impact on children's personality traits. Two adopted children raised in the exact same home are no more likely to share personality traits with each other than with a random child down the block.
Personality genetic constraints apply to other primates as well; macaque monkeys raised by foster mothers exhibited social behaviors that resembled their biological mothers rather than their foster mothers.
The Impact of Adoptive Parenting:
A Swedish study following over children born to at least one biological parent with depression found that children raised by adoptive families were approximately less likely to develop depression compared to their non-adopted biological siblings.
Parents strongly influence their children's attitudes, values, manners, politics, education, and religious faith.
Historical Case: Identical twins Jack Yufe (raised Jewish) and Oskar Stohr (raised as a Hitler Youth member in Germany). Oskar remarked upon reuniting: "If we had been switched, I would have been the Jew and you would have been the Nazi."
Screening processes make child neglect, abuse, and parental divorce rare in adoptive homes compared to unscreened biological homes.
Studies comparing biological mothers who raised some of their children while giving others up for adoption showed that adoptive mothers used gentler parenting and provided more guidance.
Outcome stats: () adopted children report feeling strongly attached to one or both adoptive parents. Adopted children tend to grow up more self-giving and altruistic, score higher on intelligence tests than their biological parents and non-adopted biological siblings, and grow into happier, more stable adults.
A Swedish study demonstrated that infants adopted at birth grew up with fewer psychological problems than children whose biological mothers initially slated them for adoption but ultimately decided to raise them themselves.
Gene-Environment Interaction:
Adaptive Capacity: The ability to adapt to differing environments is a fundamental hallmark of the human species (e.g., walking barefoot all summer produces calloused feet—a biological adaptation mechanism triggered by environmental friction).
Interaction: The interplay that occurs when the effect of one factor (such as environment) depends on another factor (such as heredity).
Genes are self-regulating rather than rigid blueprints; they react dynamically to environmental contexts. For example, an African butterfly that is green in the summer turns brown in the fall due to a temperature-controlled genetic switch.
Genetically influenced traits evoke specific reactions from others (evocative gene-environment interaction):
An attractive, friendly, easygoing baby attracts more affection and care, fostering greater social confidence.
An impulsive, aggressive child evokes angry reactions from parents or teachers, whereas well-behaved children evoke warmth.
Identical twins raised apart often recall their parents' warmth in remarkably similar terms because their shared genetic traits evoked similar parenting behaviors.
Epigenetics and Gene Expression
Mechanisms of Epigenetics:
Epigenetics: The study of the molecular mechanisms by which environments can influence genetic expression without a DNA change.
Epigenetic Marks: Organic molecules that attach to DNA segments and instruct associated genes on what to do, where to do it, and when to do it. Attachment of an epigenetic mark can switch a gene off.
Analogy: DNA is written in pen (permanent sequence); epigenetics is written in pencil (changeable expression).
Environmental influences affecting epigenetic marks include diet, chemical exposure, drugs, and psychological stress.
Experimental Evidence & Generational Transmission:
In rat experiments, infant rats deprived of maternal licking exhibited increased epigenetic modifications in the brain that persisted throughout their lifetimes.
Traumatic experiences (e.g., severe childhood trauma, poverty, malnutrition) leave molecular fingerprints on an individual's genome.
While trauma causes prolonged distress in some individuals, it increases the expression of genes linked to psychological resilience in others.
Some evolutionary biologists theorize that epigenetic changes can be passed down to subsequent generations, meaning inheritance occurs through both gene transmission and ancestral experience.
Epigenetic mechanisms explain why one identical twin may develop a genetically influenced mental disorder while the other does not, and why identical twins can exhibit minor physical differences.
In utero chemical exposure in mice causes identical twin mice to express different fur colors.
Complex developmental traits (e.g., Blue Ivy's musical talent) result simultaneously from superstar genes, a musically rich home environment, high parental expectations, and financial resources ("nature via nurture").
Evolutionary Psychology and Natural Selection
Foundational Concepts:
Evolutionary Psychology: The study of the evolution of behavior and the mind, using principles of natural selection.
Natural Selection: The principle that inherited traits that better enable an organism to survive and reproduce in a particular environment will, in competition with other trait variations, most likely be passed on to subsequent generations.
Mutation: A random error in gene replication that leads to a change.
Core Logic of Natural Selection:
An organism's offspring vary and compete for survival within an environment.
Certain biological and behavioral variations enhance survival and reproductive success in that specific environment.
Offspring that survive are most likely to pass their advantageous genes to ensuing generations.
Over time, population traits change to reflect these selective pressures.
The Dmitry Belyaev & Lyudmila Trut Fox Domestication Experiment:
Initiated in the early in Russia to determine how ancestral wolves were domesticated into dogs.
Started with female and male farm foxes.
Methodology: Tested tameness based on responses to feeding, handling, and stroking. Mated only the tamest of females and of males.
Results: Over generations, years, and foxes, Belyaev and Trut created a newly domesticated breed of fox that was docile, eager to please, barked for attention, and licked handlers like dogs.
Human Evolutionary Adaptations & Mis-matches:
Human fitness is defined as the ability to survive and reproduce in a given environment.
Shared human evolutionary tendencies evolved to solve ancestral survival problems:
Women who experienced nausea during the first trimester of pregnancy avoided bitter, novel, and strongly flavored foods, protecting the fetus from naturally occurring dietary toxins.
Ancestors who preferred energy-dense sweet and fatty foods survived periods of famine.
Evolutionary Mismatch: In modern societies, ancestral cravings for sweet and fatty foods lead to health issues due to the abundance of fast food, vending machines, and sedentary lifestyles.
Perspectives on Evolution, Science, and Faith
Scientific and Public Views on Evolution:
The application of evolutionary theory to mental processes represents the "second Darwinian revolution" envisioned by Charles Darwin in On the Origin of Species.
A editorial in the journal Nature asserted that the evolutionary origin of the human mind is an indisputable scientific fact.
Francis Collins (Director of the Human Genome Project and Christian believer) detailed in The Language of God that genetic evidence for evolution is utterly compelling.
Gallup polling reveals that approximately of US adults believe humans were created by God in their present form within the past years.
Reconciling Scientific and Spiritual Perspectives:
Science and religion offer complementary viewpoints: science explains when and how, whereas religious creation narratives focus on who and why.
Galileo Galilei stated to the Grand Duchess Christina: "The Bible teaches how to go to heaven, not how the heavens go."
Richard Dawkins noted in Unweaving the Rainbow that Isaac Newton's physical breakdown of light wavelengths did not destroy the aesthetic beauty of the rainbow, but revealed deeper underlying complexity.
Historical and religious figures affirming natural unfolding and gradual creation:
Saint Augustine (): Stated that the universe was brought into being in a less-than-fully-formed state with the capacity to transform itself over time.
Ibn Khaldun ( Muslim historian): Noted in his writings that creation progressed gradually from minerals to plants and animals.
Pope Francis (): Stated that evolution in nature is consistent with divine creation because evolution requires the creation of beings that evolve.
Cosmic Fine-Tuning and Evolutionary Scale:
The Big Bang occurred approximately years ago.
Astronomer Sir Martin Rees highlighted fundamental physical constants; if any of these numbers were altered even slightly, the universe would either have collapsed back on itself or expanded into a gas too thin to support life.
Astrophysicist Owen Gingerich noted that the universe appears expressively fine-tuned to produce intelligent, sentient life.
Philosopher Ludwig Wittgenstein advised: "Whereof one cannot speak, thereof one must be silent."
Lewis Thomas noted the awe of life evolving over years from single-celled bacteria to structures as complex as a strand of DNA ( units), the human brain, and cultural achievements like Bach's Mass in B Minor.