Genetics, Development, and Psychology: Key Concepts

Posted on Feb 20, 2025 in Podiatry

Behavior Genetics and Human Development

Behavior geneticists: study how heredity and environment contribute to human differences.

Genes: Biochemical units of heredity that make up chromosomes: the threadlike coils of DNA.

Gene expression: The code for creating the proteins that form our body’s building blocks.

Chromosome: Threadlike structure made largely of DNA molecules.

DNA: A spiraling, complex molecule containing genes.

The Human Genome

The human genome contains approximately 20,000 to 25,000 genes.

The genome: an organism’s entire collection of genes.

Chromosomes and Inheritance

The human genome includes 46 chromosomes in 23 matched sets; each chromosome has the same gene locations. This includes the X and Y chromosomes, not a matched set in males, who are missing some genes on the Y. A biological parent donates half his/her set of chromosomes to his/her offspring. We receive half a set of chromosomes from each biological parent.

How Genes Work

Genes are not blueprints; they are molecules.

Molecules have the ability to direct the assembly of proteins that build the body.

This genetic protein assembly can be turned on and off by the environment, or by other genes → EPIGENETICS!

Down’s syndrome is caused by a 3rd copy of Chromosome 21, effectively giving individuals with Down’s syndrome 47 chromosomes total.

Any trait we see is a result of the complex interactions of many genes and countless other molecules. There is rarely one single gene for one trait.

Epigenetics and Gene Expression

EPIGENETICS INFLUENCES GENE EXPRESSION: Life experiences beginning in the womb lay down epigenetic marks—often organic methyl molecules—that can affect the expression of any gene in the associated DNA segment.

When genetics are held constant:

  • Personality traits such as extraversion (sociability) and neuroticism (emotional instability).
  • Behaviors/outcomes such as the rate of divorce.
  • Abilities such as overall Intelligence test scores.

Similarities in Twins Raised in Different Homes

Personality, styles of thinking and relating, abilities/intelligence test scores, attitudes, interests, tastes, specific fears, brain waves, heart rate.

Biological vs. Adoptive Relatives

Adopted children seem to be more similar to their genetic relatives than their environmental/nurture relatives. Parenting influence: Religious beliefs, values, manners & attitudes, politics & habits.

Why are Siblings Different?

  • Siblings only share half their genes.
  • Genetic differences become amplified as people react to them differently.
  • The environment changes with each addition to a family.
  • Siblings are raised in slightly different families; the youngest has more older siblings and has older parents.

Temperament

A person’s general level and style of emotional reactivity – apparent from first weeks of life and generally persists into adulthood.

Three Types of Temperament in Infancy

  • “Easy” → cheerful & relaxed, predictable
  • “Difficult” → fidgety, intense, irritable
  • “Slow to warm up” → resisting or withdrawing from new people/situations

WHY? Biological explanations: Anxious, inhibited infants have fast and variable heart rates and a reactive nervous system. Experience matters. Supportive parenting can reduce the impact of early withdrawal, and unsupportive parenting or trauma can bring out the anxious, inhibited personality in a child who is predisposed to this temperament.

Heritability

When you see a variation of some trait within a population, the heritability of that trait is the amount of variation in the population that is explained by genetic factors. This DOES NOT tell us the proportion that genes contribute to the trait. The heritability of a trait also does not tell us whether genetics explain differences between groups/populations.

Heritability Estimates

  • Height: 55-90%
  • Alcoholism: 50-60%
  • Depression: 50%
  • Obesity: 70%
  • Schizophrenia: 81%

Evolutionary Psychology

Evolutionary psychology is the study of the evolution of behavior and the mind using principles of natural selection. Some variations arise from mutations; others from new gene combinations at conception.

How Has Evolution Shaped the Human Species?

Adaptive flexibility in responding to different environments contributes to the ability to survive and reproduce. Example: Why does “stranger anxiety” develop between the ages of 9 and 13 months? Humans are learning to walk at that time. Possible explanation: Infants who used their new ability to walk by walking away from family and toward a lion might not have survived to reproduce as well as those who decided to cling to parents around the time they learned to walk.

Evolutionary Psychology’s Explanation of Phobias

Why do people so easily acquire a phobia of snakes? An evolutionary psychologist would note that snakes are often poisonous…so those who more readily learned to fear them were more likely to survive and reproduce.

Human Genetic Legacy

“Illogical” Moral Reasoning: It might be “logical” to kill one innocent person if it would enable five other innocent people to live. Research shows that most people (regardless of culture) can imagine letting the one person die (to save many), but cannot picture killing the person themselves.

Male and Female Differences: Focusing on Mating Preferences

First issue: quantity (of mating). Generally, men think more than women about sex, and men are more likely to think that casual sex is acceptable. Men who had the trait of promiscuity were more likely to have their genes continue, and even spread, in the next generation. And there is little cost to spreading extra genes. For women, a trait of promiscuity would not greatly increase the number of babies, and it would have greater survival costs (pregnancy, once a life-threatening condition).

Evolutionary Strategies in Seeking Partners

Men seek women with a fuller figure…to make sure they are not too young or too old to have children? Women seek males with loyal behavior and physical/social power and resources…

…in order to ensure the survival of the mother’s offspring?

Critiques of Evolutionary Psychology

Most psychologists agree that natural selection prepares humans for survival and reproduction. Critics of evolutionary psychology research often start with effect and work backward. More immediate explanations for results better understood by social learning theory than decisions made by very distant ancestors. Social consequences of explanation are problematic. Some traits and behaviors are difficult to explain by natural selection.

Experience and the Brain

Rats alone or with other rats in an environment enriched with playthings changed daily. Handled infants develop faster neurologically!

Nature and Nurture Interaction

Shape synapses to make well-used brain pathways work better, unused connections are “pruned” away. This means that if certain abilities are not used, they will fade. Brain development does not end with childhood. Plasticity allows neural tissue to change and reorganize in response to new experience.

Blame or Credit? The Role of Parents

Freudian psychiatry, psychology, and society blame a host of negative child behaviors on “bad mothering.” The largest parenting effects occur at the extremes: abuse or loving. In personality measures, shared environmental influences from prenatal development onward account for less than 10 percent of child differences.

Parents may try to have indirect influence by selecting a child’s peers, such as by selecting a school or neighborhood. However, ultimately, most children self-select their peers. The degree of peer influence is hard to trace. Apparent conformity could be a selection effect. Interaction with peers can teach new social skills. Gardner (1998) concluded parents and peers are complementary.

Parents vs. Peers

Parents have more influence on:

  • Education and career path
  • Cooperation, self-discipline, responsibility, charitableness, religion
  • Interaction style with authority figures

Peers have more influence on:

  • Learning cooperation skills
  • Learning the path to popularity
  • Choice of music and other recreation
  • Choice of clothing and other cultural choices
  • Good and bad habits

Cultural Influences

Nature of Culture: Refers to the patterns of ideas, attitudes, values, lifestyle habits, and traditions shared by a group of people and passed on to future generations. Culture is not just an influence on our nature, but it is also part of our nature. Humans form not only relationships, but culture.

Variation Across Cultures

Each culture has norms–standards for acceptable, expected behavior. Culture shock: feeling lost about what behaviors are appropriate.

Cultural Variation Over Time

  • Language changes in vocabulary and pronunciation.
  • Pace of life quickens.
  • Gender equality increases.
  • People sleep less, socialize in person less, stare at screens more.
  • People marry more for love, but then expect more romance.

These cultural changes occur too fast to be rooted in genetic change.

Culture Influences on Development and the Self: Individualism and Collectivism

Individualist cultures value independence. They promote personal ideals, strengths, and goals, pursued in competition with others, leading to individual achievement and finding a unique identity. Collectivist cultures value interdependence. They promote group and societal goals and duties, and blending in with group identity, with achievement attributed to mutual support.

Value Concepts Between Individualism and Collectivism

  • Self-independent vs. interdependent
  • Life task – discover and express one’s uniqueness vs. maintain connections, fit in
  • What matters – me, rights & liberty, US vs. group goals, social responsibility
  • Coping method – change reality vs. accommodate to reality
  • Morality – self-based vs. duty-based social networks
  • Relationships – many acceptable, few enduring, harmony valued
  • Attributing behavior – Behavior reflects one’s personality vs. behavior reflects social norms.

Culture and Child Raising

Parents everywhere care about their children, but raise and protect them differently depending on the surrounding culture. People in individualist cultures might raise children to be self-reliant and independent.

PARENTAL INVOLVEMENT PROMOTES DEVELOPMENT: Cultures differ in what they deem important.

Cognition

All the mental activities associated with thinking, knowing, remembering, and, including:

  • Problem-solving.
  • Figuring out how the world works.
  • Developing models and concepts.
  • Storing and retrieving knowledge.
  • Understanding and using language.
  • Using self-talk and inner thoughts.

Jean Piaget (1896 – 1980)

Considered the father of modern developmental psychology. Cognitive Developmental Theory:

  • Children are active thinkers.
  • Children’s maturing brains build schemas which are used and adjusted through assimilation and accommodation.
  • Minds develop through series of universal, irreversible stages from simple reflexes to adult abstract reasoning.

Vygotsky’s Sociocultural Theory

Importance of adult and older peer interactions to facilitate a child’s development. Vygotsky did not believe that play was useful in the development of children’s cognitive skills. Social interaction is necessary for children to acquire the ways of thinking and behaving that make up a community’s culture.

Schemas

Can take the form of images, models, and/or concepts, e.g., cows.

Piaget’s Stages of Cognitive Development

  • Combination of nature and nurture. Children grow by maturation as well as by learning through interacting/playing with the environment.
  • Is not one continuous progression of change. Children make leaps in cognitive abilities from one stage of development to the next.

Age Range, Stage, Developmental Phenomena

  • Age 2, sensorimotor: experience the world through senses actions looking hearing touching
  • Age 2-6-7, preoperational: representing things with words images, pretend play egocentrism
  • 7-11 concrete operational: thinking logically, conservation mathematical transformations
  • 12, formal operational: abstract reasoning, abstract logic potential for mature moral reasoning.

Sensorimotor Stage (2 yrs)

Infants acquire information about the world by sensing it and moving around within it. Object permanence. Researchers today believe Piaget underestimated young children’s competence baby physics and baby math.

Preoperational Stage (2-7)

Child learns to use language can’t perform mental operations of concrete logic. Conservation- a substance’s weight, mass and volume remain the same even if it changes shape; child masters during concrete operational stage (7-11 years). Egocentrism- In the realm of cognitive development, it refers to a lack of differentiation in some area of subject – object interaction.

Older Stages

Concrete operational (7 to 11 years): Children gain the mental operations that enable them to think logically about concrete events. They begin to understanding change in form before change in quantity. Formal operational (12 through adulthood): Children are no longer limited to concrete reasoning based on actual experience. They are able to think abstractly.

Lev Vygotsky (1896-1934)

Studied kids too, but focused on how they learn in the context of social communication. Jean Piaget was more focused on how children learned through interaction with the physical environment.

Reflecting on Piaget

Piaget identified significant cognitive milestones and stimulated global interest in cognitive development. Development is more continuous than Piaget theorized. Children may be more competent than Piaget’s theory revealed.

Autism Spectrum Disorder (ASD)

Impaired theory of mind, social deficiencies, and repetitive behaviors. Many genes have been identified as playing a role (+200). Random mutation in sperm. Underconnectivity within the brain.

Prevalence of ASD

By age 8, 1 in 68 U.S. children now gets diagnosed with ASD.

Social Development

Parent – infant bonds: the brain, mind, and social emotional behavior develop together.

Familiarity

Imprinting: Process by which certain animals form strong attachments during early life. Children attach to what they’re familiar with safety familiarity.

Attachment Differences: Reactions to Separation and Reunion

  • Secure attachment: most children (60 percent) feel distress when mother leaves, and seek contact with her when she returns.
  • Insecure attachment (avoidant style): seeming indifferent to mother’s departure and return.

Attachment Styles: Nature or Nurture?

Inborn temperament where a person’s characteristic style and intensity of emotional reactivity. Attachment theory says it either permits us to be loving, successful adults or produces lasting emotional scars—early life experiences with caregivers shape our lifelong ability to love.

Nature vs. nurture: the interaction between our genetic inheritance and our experiences.

Deprivation of Attachment

Lower intelligence scores, attachment problems.

Parenting Styles

Degrees of control (Baumrind). Authoritative parents tend to have children with the highest self-esteem, self-reliance, and social competence.

Permissive parents tend to have children who are more aggressive and immature.

Authoritarian parents tend to have children with less social skills and self-esteem.

Two Alternatives to Parent/Child Outcome Link

  • Children’s trait may influence parenting.
  • Underlying 3rd factors – genes predisposing certain outcomes (in the form of social competence).