Nature, nurture and the shape of change

Transcript

RyanTwo new mothers, close friends, with children around the same age. One has a daughter who is fourteen months old and still isn't walking. The other has a son who started walking at ten months. And the first mom tells her friend she's worried something might be wrong.

SoheeThat little scene is straight out of the OpenStax psychology textbook, and I love it, because it holds almost every big question in developmental psychology.

RyanWelcome to EPPP Prep, the podcast. I'm Ryan.

SoheeAnd I'm Sohee. This is the first episode in our run on Growth and Lifespan Development, which is twelve percent of the exam. Today is the foundation: the questions every developmental theory is trying to answer.

RyanBecause once you can see those questions, the theories stop feeling like a pile of names. They become different answers to the same few puzzles.

SoheeLet's start with the map. Developmental psychologists study change across three domains. Physical development is growth and change in the body and brain, the senses, motor skills, and health and wellness.

RyanCognitive development is learning, attention, memory, language, thinking, reasoning, and creativity. And psychosocial development is emotions, personality, and social relationships.

SoheeNow back to our worried mom. The textbook uses her to explain the normative approach. In the early twentieth century, researchers studied large numbers of children to find norms, meaning the average ages when most children reach specific milestones.

RyanAnd the norm the textbook gives for walking is twelve months. So her daughter is a bit past the average. But an average is a midpoint, not a deadline.

SoheeThe Lifespan Development textbook makes that point beautifully. Scientific ideas about development represent statistical averages across many people, but every individual is unique and has their own life history.

RyanWhat matters more is the sequence, and whether it happens within a typical timeframe. One child saying two-word phrases early doesn't overturn the research.

SoheeOne more nuance. Not every normative event is universal. Biological milestones, like puberty, tend to be universal. Social milestones, like the age children start school, depend on the culture.

RyanOkay. Big question number one. Is development continuous or discontinuous?

SoheeContinuous development is cumulative. It gradually improves on existing skills. The classic example is a child adding inches to their height year by year.

RyanDiscontinuous development happens in unique stages, at specific times or ages, and the change is more sudden. The textbook's example is an infant coming to grasp object permanence.

SoheeAnd that's why we call the discontinuous theories stage theories. Lifespan Development says a stage theory tries to explain why we see brief periods of rapid development followed by longer stretches of stability.

RyanPiaget and Erikson are the classic stage theorists. But here's a subtle point the exam can use. Something can look discontinuous and still have continuous change underneath it.

SoheePuberty is the example. Its changes seem sudden, but when researchers look at the hormone changes that prepare the body, continuous patterns show up too.

RyanMeanwhile, vocabulary growth in the toddler and early childhood years is described as dramatic but smooth. That's a continuous pattern.

SoheeAnd there's an assumption hiding in all of this. Development is progressive. It moves forward. Moving back to an earlier stage or a lower capability is called regression, and it's a sign that something may be wrong.

RyanBig question number two. Is there one course of development, or many?

SoheeStage theories hold that the sequence is universal. And there's support for that. Across cultures, infants coo before they babble, and they say their first word around twelve months.

RyanBut the timing can bend with culture. The psychology textbook describes the Aché people of Paraguay. Mothers carry their young children while foraging in the forest, rarely putting them down, to protect them.

SoheeSo Aché children walk at around twenty-three to twenty-five months, compared with around twelve months for infants in Western cultures. But by about age nine, their motor skills surpass those of children in the United States. They climb trees up to twenty-five feet tall.

RyanSo the functions are present everywhere, but the timing varies with context. Lifespan Development adds a modern study: Israeli parents encouraged more tummy time than Dutch parents, and the Israeli babies showed better crawling skills.

SoheeBig question number three, the famous one. Nature and nurture.

RyanAnd notice the word and. Lifespan Development says the field used to ask whether it was nature or nurture. Now it recognizes that most development has both genetic and environmental influences.

SoheeThe extent to which the genetic component explains differences is called a heritability estimate. The behavioral genetics section frames it as how much variation in a characteristic is due to genetic differences among individuals.

RyanTheir example of both at work is the timing of puberty. Genes play a role, and so does nutrition.

SoheeThen there's reaction range. The idea is that our genes likely set upper and lower limits for a trait, and also how sensitive that trait is to the environment.

RyanNow the part the exam loves: gene-environment correlation. Three types. Passive, evocative, and active.

SoheePassive is when a child inherits genes from their parents that also shape the environment they're raised in. Parents who enjoy reading are more likely to read to their kids and keep lots of books in the house.

RyanEvocative is when a child's genetically influenced behavior draws reactions from other people. Parents notice their child enjoys reading, so they take her to the library.

SoheeAnd active is when a person's genetic tendencies lead them to choose environments. The child joins a book club at school because she loves reading.

RyanPause and think. A teenager with a natural gift for music signs up for every band and choir she can find. Her music teacher, impressed, starts giving her solos. Which two types are those?

SoheeSigning up herself is active. She's selecting her environment. The teacher responding to her talent is evocative. Her behavior evoked a reaction. If her parents were musicians who filled the house with instruments before she could choose anything, that would be passive.

RyanOne more piece of the nature and nurture story: epigenetics. That's how a person's behaviors and environment can change the way their genes work.

SoheeLifespan Development says there's evidence that stressful environments can trigger a chemical tagging of someone's DNA. So experience can reach all the way down to how genes are expressed.

RyanLast big theme: timing. Are there windows of opportunity? Here the exam tests two terms that sound almost the same.

SoheeA critical period is an age range in which certain experiences are required for an ability to develop. Required. A sensitive period is an age range when development is particularly open to environmental input.

RyanSo in a critical period, the experience is necessary for normal development. In a sensitive period, the experience is advantageous, it makes ideal development more likely.

SoheeThe example for critical periods is language, and the case of Genie. In 1970, a social worker near Los Angeles found a thirteen-year-old girl who'd been raised in extremely neglectful and abusive conditions, with virtually no social interaction.

RyanAfter her rescue, her abilities improved dramatically. She built an impressive vocabulary. But the psychology textbook says she never mastered the grammatical aspects of language.

SoheeAnd Lifespan Development adds a striking detail. For the vast majority of people, language is processed in the left hemisphere. Genie showed language processing in her right hemisphere.

RyanPause and think, second one. A coach times training around the growth spurts of puberty, because that's when training has the most impact. Critical or sensitive?

SoheeSensitive. Nothing is impossible later. That's just the window when input helps most. That's actually the textbook's own example of a sensitive period.

RyanAnd here's the hopeful counterweight, which I want every listener to hear. Lifespan Development says humans are highly adaptable, and that it takes extreme deprivation to severely restrict a person's potential. In their words, resilience is common.

SoheeLet's talk about how the exam tests this. First, look for the word stages, or sudden qualitative shifts. That points to discontinuous, stage theories. Gradual, cumulative growth points to continuous.

RyanSecond, gene-environment correlation. Ask who is choosing the environment. The parents, through what they provide? Passive. Other people reacting to the child? Evocative. The person themselves? Active.

SoheeThird, critical versus sensitive. If the stem says the experience is necessary, critical. If it says most responsive or optimal, sensitive.

RyanLet's recap. Three domains: physical, cognitive, psychosocial. The normative approach gives average ages for milestones, and averages describe groups, not deadlines for any one child.

SoheeContinuous change is gradual and cumulative. Discontinuous change comes in stages. The sequence of many milestones is shared across cultures, but timing varies with context, like Aché walking.

RyanNature and nurture work together. Heritability is about differences among people. Gene-environment correlation is passive, evocative, or active. And epigenetics shows experience shaping gene expression.

SoheeA critical period means the experience is required. A sensitive period means it helps most. And resilience is common.

RyanSo, should that mom be worried? The textbooks would say watch the pattern, and talk to the pediatrician if several milestones are delayed. And honestly, the same advice works for you.

SoheeYour study path has its own timeline, and it doesn't have to match anyone else's. You just built the frame that every other episode in this domain hangs on. That's real progress. Thanks for listening to EPPP Prep.

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