Development Across the Life Span

This chapter answers Section XH5.9 of XH5 Psychology, one of the six optional sections of the Humanities and Social Sciences (XH) paper, chosen at application: “Nature versus nurture in human development, Prenatal development: Chromosomes, Genes and DNA. Physical, cognitive and psychosocial development in infancy, childhood, adolescence and adulthood. Moral development. Theories of aging.” It teaches the heredity-environment question, the biological foundations and stages of prenatal growth, the major physical, cognitive (Piaget, Vygotsky) and psychosocial (Erikson, attachment) changes from birth to old age, the accounts of moral development (Piaget and Kohlberg), and the biological and social theories of ageing.

1. Nature, nurture and prenatal development

The nature-nurture debate asks how much of development is shaped by heredity (genes) and how much by environment (experience). The modern answer is interactionist: the two work together, genes set a range of possibilities (a reaction range) and the environment determines where within it a person falls, while epigenetics shows experience can switch genes on or off without changing the DNA sequence. To estimate the split, psychologists use twin studies (comparing identical and fraternal twins) and adoption studies (comparing children with their biological and adoptive parents). Heritability is a population statistic — the proportion of the variation in a trait across a group that is linked to genetic differences — and does not say what caused the trait in any single individual.

Biologically, the instructions sit in DNA, a double-helix molecule; a gene is a segment of DNA that codes for a protein; and genes are packaged into chromosomes. A typical human body cell has 46 chromosomes in 23 pairs — 22 pairs of autosomes and one pair of sex chromosomes (XX in a female, XY in a male). At conception a sperm and ovum, each carrying 23 chromosomes, form a 46-chromosome zygote. Prenatal development then runs in three periods: the germinal period (about the first two weeks, rapid cell division and implantation), the embryonic period (about weeks two to eight, when the major organs and systems first form and vulnerability to teratogens is greatest), and the fetal period (about week eight to birth, growth and refinement).

⚠️ Heritability is about variation, not individuals
A heritability of 0.5 for a trait does not mean half of any one person's trait came from genes. It means that, in the population studied and its particular environment, about half of the differences between people are statistically linked to genetic differences. Change the environment and the figure changes. Reading heritability as a claim about a single individual is the standard error.

2. Physical development across the life span

Newborns arrive with a set of adaptive reflexes (rooting, sucking, grasping, the Moro or startle reflex), most of which fade as voluntary control develops. Early physical growth follows two directions: the cephalocaudal principle, from the head downward, so an infant controls the head before the legs; and the proximodistal principle, from the body's centre outward, so control of the trunk and arms precedes fine finger control. Motor milestones (sitting, crawling, walking) appear in a fairly fixed order, though their timing varies.

Adolescence opens with puberty, a surge of hormones that brings the growth spurt, primary sex characteristics (the maturing of the reproductive organs) and secondary sex characteristics (such as body hair and voice change); menarche and spermarche mark reproductive capacity. In adulthood, physical capacities peak in the twenties and then decline gradually; in middle adulthood women reach menopause, the end of menstruation and fertility. It is useful to separate primary ageing — the intrinsic, universal biological changes of growing older — from secondary ageing — the changes caused by disease, disuse and lifestyle, which are far more variable and more open to prevention.

3. Cognitive development: Piaget and Vygotsky

Jean Piaget saw the child as an active builder of knowledge who organises experience into schemas and revises them through assimilation (fitting new input into an existing schema) and accommodation (changing the schema to fit new input), driven toward equilibration. He proposed four universal stages in a fixed order: the sensorimotor stage (roughly birth to two years), ending in object permanence; the preoperational stage (about two to seven), marked by symbols and language but also by egocentrism and a failure of conservation; the concrete operational stage (about seven to eleven), when the child conserves and reasons logically about concrete things; and the formal operational stage (about eleven onward), bringing abstract and hypothetical reasoning.

Lev Vygotsky agreed the child is active but put social interaction and language at the centre: higher thinking is internalised from guided activity with more knowledgeable others. His key idea, the zone of proximal development (ZPD), is the gap between what a learner can do alone and what they can do with help; good teaching, through scaffolding, works in this zone, so for Vygotsky learning can lead development rather than merely follow it. Where Piaget stressed universal maturational stages, Vygotsky stressed culture and instruction. Information-processing accounts add a third view, treating development as gradual gains in attention, memory capacity and processing speed rather than discrete stages.

🧠 Spotting the preoperational child
The classic sign is failing conservation: pour the same water into a taller, thinner glass and the preoperational child says there is now 'more', fooled by the height because they cannot mentally reverse the pour or attend to two dimensions at once. Passing conservation marks the move into concrete operational thought.

4. Psychosocial development and attachment

Erik Erikson described development as eight psychosocial stages, each a crisis between two poles whose resolution shapes the next. In order they are: trust versus mistrust (infancy), autonomy versus shame and doubt (toddlerhood), initiative versus guilt (preschool), industry versus inferiority (school age), identity versus role confusion (adolescence), intimacy versus isolation (young adulthood), generativity versus stagnation (middle adulthood) and integrity versus despair (late adulthood). Unlike Freud, Erikson ran development across the whole life span and emphasised social rather than purely sexual forces.

Two extensions are standard. James Marcia refined Erikson's adolescent crisis into four identity statuses, defined by whether the person has explored alternatives (crisis) and made a commitment: identity diffusion (no exploration, no commitment), foreclosure (commitment without exploration), moratorium (exploring, not yet committed) and identity achievement (committed after exploring). Diana Baumrind described three parenting styles: authoritative (high warmth and firm, explained limits, usually linked with the best child outcomes), authoritarian (high control, low warmth) and permissive (high warmth, few limits); a fourth, neglectful, was added later by Maccoby and Martin.

Attachment is the enduring emotional bond between infant and caregiver. John Bowlby argued it is biologically based, serving survival; Harry Harlow's monkeys, who clung to a soft cloth 'mother' over a wire one that fed them, showed that contact comfort, not feeding alone, underlies it. Mary Ainsworth's Strange Situation procedure classified infants by their response to separation and reunion: secure (explores from the caregiver, distressed at parting, soothed on reunion), insecure-avoidant (little distress, avoids the caregiver), insecure-resistant/ambivalent (very distressed, hard to soothe), and the later-added disorganised pattern (confused, contradictory behaviour).

5. Moral development: Piaget and Kohlberg

Piaget distinguished two broad stages of moral reasoning. Younger children show heteronomous morality (moral realism): rules are fixed and handed down by authority, and an act's wrongness is judged by the size of its consequences. Older children, from about ten, show autonomous morality (moral relativism): rules are seen as social agreements that can change, and intention matters more than outcome. The shift comes with cognitive growth and peer cooperation.

Lawrence Kohlberg extended this using moral dilemmas (famously the Heinz dilemma) and proposed three levels, each with two stages, six stages in all. At the preconventional level morality is judged by consequences to the self: stage 1 is punishment-and-obedience, stage 2 is instrumental self-interest and simple exchange. At the conventional level it rests on social approval and order: stage 3 is 'good boy / nice girl' seeking approval, stage 4 is law-and-order. At the postconventional level it rests on abstract principles: stage 5 is a social contract that can be revised for the common good, stage 6 is self-chosen universal ethical principles. Carol Gilligan objected that Kohlberg's scheme, built from male samples, undervalued an 'ethic of care' alongside his 'ethic of justice'.

6. Theories of ageing

Biological theories of ageing fall into two families. Programmed theories treat ageing as following an internal biological timetable — a genetic clock, hormonal and immune changes, and the limited number of times cells can divide (telomeres shorten with each division). Damage or error theories treat ageing as the accumulation of wear: oxidative damage from free radicals, cross-linking of proteins, and random mutations build up until function fails. The two are not exclusive; most researchers see ageing as programmed limits plus accumulated damage.

  • Disengagement theory (Cumming and Henry): ageing involves a natural, mutual withdrawal of the older person and society from each other, which the theory treats as functional.
  • Activity theory (Havighurst): well-being in later life depends on staying active and keeping up social roles and engagement, the near-opposite of disengagement.
  • Socioemotional selectivity theory (Carstensen): as the time left in life is perceived as limited, people deliberately narrow their networks to emotionally meaningful relationships and prioritise emotional goals over information-seeking ones.

Key takeaways

  • Development is interactionist: genes set a reaction range, environment places a person within it, and epigenetics lets experience switch genes on or off. Twin and adoption studies estimate the heredity-environment split; heritability is a population statistic about variation, never a claim about one individual.
  • A human cell has 46 chromosomes in 23 pairs (22 autosome pairs plus XX or XY); a gene is a DNA segment coding a protein. Prenatal development runs germinal, embryonic (organs form, teratogens most dangerous) and fetal periods.
  • Physical growth is cephalocaudal (head down) and proximodistal (centre out); puberty brings the growth spurt and sex characteristics, and menopause ends fertility. Primary ageing is intrinsic and universal; secondary ageing comes from disease and lifestyle.
  • Piaget's four stages are sensorimotor (object permanence), preoperational (egocentrism, no conservation), concrete operational (conservation, logic on concrete things) and formal operational (abstract reasoning). Vygotsky stressed social interaction, language and the zone of proximal development, where learning can lead development.
  • Erikson's eight psychosocial stages run from trust-versus-mistrust in infancy to integrity-versus-despair in late life, with identity-versus-role-confusion the crisis of adolescence. Attachment (Bowlby) is shown by Ainsworth's Strange Situation as secure, insecure-avoidant, insecure-resistant or disorganised.
  • Piaget's moral stages are heteronomous (rules fixed, outcome judged) then autonomous (rules negotiable, intention judged). Kohlberg's three levels, six stages, run preconventional (punishment, self-interest), conventional (approval, law-and-order) and postconventional (social contract, universal principles). Ageing theories are programmed, damage/error, and the social accounts of disengagement, activity and socioemotional selectivity.

Practice questions (18)

Attempt each one before opening the answer. Every explanation names the tempting wrong option as well as the right one, because that is where marks are lost.

  1. The genetic material of a typical human body cell is organised in which way?

    1. Into 23 pairs of chromosomes, 22 pairs of autosomes together with one pair of sex chromosomes
    2. Into 46 pairs of chromosomes, with one whole pair being contributed by each of the parents
    3. Into a single continuous strand of DNA that is not divided into any separate chromosomes
    4. Into 23 single chromosomes in total, which is exactly half the number carried by a gamete
    Show answer

    Answer: A — Into 23 pairs of chromosomes, 22 pairs of autosomes together with one pair of sex chromosomes

    A human body (somatic) cell has 46 chromosomes arranged as 23 pairs: 22 autosome pairs and one sex-chromosome pair (XX or XY). '46 pairs' doubles the count; a gamete, not a body cell, has 23 single chromosomes, so the choice describing 23 single chromosomes in a body cell inverts the relationship; and DNA is in fact packaged into chromosomes.

  2. To estimate the relative contributions of heredity and environment to a human trait, developmental psychologists rely most directly on:

    1. Case studies that follow a single unusual individual in great depth over many years
    2. Twin studies and adoption studies, which help disentangle heredity from shared environment
    3. Cross-sectional opinion surveys that measure people's reported attitudes at one point in time
    4. The method of free association that was borrowed from classical psychoanalytic practice
    Show answer

    Answer: B — Twin studies and adoption studies, which help disentangle heredity from shared environment

    Comparing identical with fraternal twins, and children with their biological versus adoptive parents, is how the heredity-environment contributions are teased apart. A single case study cannot separate the two; attitude surveys and free association address different questions entirely.

  3. During which prenatal period do the major organs and body systems first take shape, making it the time of greatest vulnerability to teratogens?

    1. The germinal period, the roughly two weeks of rapid cell division just after conception
    2. The embryonic period, roughly weeks two to eight, when the major organs first take shape
    3. The fetal period, from about the eighth week until birth, a long time of growth and refinement
    4. The perinatal period, the short span of time immediately surrounding the birth itself
    Show answer

    Answer: B — The embryonic period, roughly weeks two to eight, when the major organs first take shape

    Organ formation (organogenesis) happens in the embryonic period, weeks two to eight, which is therefore when teratogens do the most structural harm. The germinal period is implantation; the fetal period is growth and refinement of organs already formed; the perinatal period is around birth, long after organogenesis.

  4. The principle that early physical growth and motor control proceed from the head downward toward the feet is known as:

    1. The cephalocaudal principle, by which growth proceeds from the head downward toward the feet
    2. The proximodistal principle, by which growth proceeds from the body's centre outward to the limbs
    3. The principle of equilibration, by which the mind balances assimilation against accommodation
    4. The principle of canalization, by which heredity keeps development within a narrow set path
    Show answer

    Answer: A — The cephalocaudal principle, by which growth proceeds from the head downward toward the feet

    Head-downward growth is the cephalocaudal principle, which is why head control precedes walking. The proximodistal principle is centre-outward growth; equilibration and canalization are concepts from cognitive development and genetics respectively, not directions of physical growth.

  5. In the study of ageing, how are primary ageing and secondary ageing correctly distinguished?

    1. Primary ageing refers to the changes caused by particular diseases and lifestyle habits, while secondary ageing refers to the intrinsic, universal biological changes of growing older
    2. Primary ageing refers to changes occurring before birth, while secondary ageing refers to changes occurring across childhood
    3. Primary ageing refers to the decline of cognition, while secondary ageing refers to changes of personality and social roles
    4. Primary ageing refers to the intrinsic, universal biological changes of growing older, while secondary ageing refers to the changes caused by disease, disuse or lifestyle
    Show answer

    Answer: D — Primary ageing refers to the intrinsic, universal biological changes of growing older, while secondary ageing refers to the changes caused by disease, disuse or lifestyle

    Primary ageing is the intrinsic, universal biological decline that happens to everyone; secondary ageing is the variable, often preventable decline caused by disease, disuse and lifestyle. The choice that gives primary ageing the disease-and-lifestyle meaning reverses these two definitions; the before-birth/childhood and cognition/personality options describe neither term.

  6. In Piaget's theory, the understanding that objects continue to exist even when they can no longer be seen (object permanence) is the key achievement of which stage?

    1. The preoperational stage, when the child uses symbols but cannot yet reason logically
    2. The concrete operational stage, when the child can reason logically about concrete things
    3. The sensorimotor stage, when the infant comes to grasp that hidden objects still exist
    4. The formal operational stage, when the person can reason about abstract and hypothetical ideas
    Show answer

    Answer: C — The sensorimotor stage, when the infant comes to grasp that hidden objects still exist

    Object permanence develops across the sensorimotor stage (birth to about two years) and is its hallmark achievement. The preoperational, concrete operational and formal operational stages are later and are defined by other milestones (symbols, conservation and abstract reasoning respectively).

  7. A child agrees that two identical glasses hold the same amount of juice, but after the juice from one is poured into a taller, thinner glass, insists the tall glass now has more. Piaget would place this child in which stage?

    1. The preoperational stage, in which children cannot yet conserve quantity across a change in shape
    2. The concrete operational stage, in which children have mastered the conservation of quantity
    3. The formal operational stage, in which adolescents can reason systematically about abstract cases
    4. The sensorimotor stage, in which infants come to learn through their senses and their movements
    Show answer

    Answer: A — The preoperational stage, in which children cannot yet conserve quantity across a change in shape

    Failing conservation — thinking the taller glass has more because it looks taller — is the signature of preoperational thought. A concrete operational child would conserve and say the amount is unchanged; formal operational and sensorimotor concern abstract reasoning and infant sensory learning, not this error.

  8. A central way in which Vygotsky's account of cognitive development differs from Piaget's is that Vygotsky:

    1. held that children everywhere must pass through exactly the same fixed universal stages, always in the same unvarying order, whatever their culture
    2. denied that children play any active part in constructing their own understanding of the world
    3. claimed that cognitive development is essentially complete by the end of early infancy
    4. stressed that development is driven by social interaction and language, with learning leading development within the zone of proximal development
    Show answer

    Answer: D — stressed that development is driven by social interaction and language, with learning leading development within the zone of proximal development

    Vygotsky's distinctive claim is that social interaction and language drive development, and that instruction within the zone of proximal development can lead development. Fixed universal stages in every culture is Piaget's position, not Vygotsky's; both theorists see the child as active (so the denial is false); and neither says development ends in infancy.

  9. In Erikson's theory of psychosocial development, the central crisis of adolescence is:

    1. Trust versus mistrust, which is resolved through reliable and responsive early caregiving
    2. Identity versus role confusion, the search for a coherent sense of self and direction
    3. Intimacy versus isolation, the young-adult task of forming close and committed relationships
    4. Integrity versus despair, the late-life review of whether one's life has had real meaning
    Show answer

    Answer: B — Identity versus role confusion, the search for a coherent sense of self and direction

    Adolescence centres on identity versus role confusion — forming a stable sense of who one is. Trust versus mistrust is infancy, intimacy versus isolation is young adulthood, and integrity versus despair is late adulthood, so each of those belongs to a different stage of the life span.

  10. In Ainsworth's Strange Situation, an infant who explores freely while the caregiver is present, becomes distressed when the caregiver leaves, and is quickly comforted and resumes play on reunion, is classified as:

    1. Securely attached, using the caregiver as a safe base and being readily comforted on their return
    2. Insecure-avoidant, showing little distress at separation and tending to ignore the caregiver on return
    3. Insecure-resistant, being intensely distressed at separation and remaining hard to soothe on return
    4. Disorganised, showing confused or contradictory behaviour with no consistent coping strategy
    Show answer

    Answer: A — Securely attached, using the caregiver as a safe base and being readily comforted on their return

    Exploring from a secure base, distress at separation, and easy comfort on reunion is the profile of secure attachment. Avoidant infants show little distress and ignore the caregiver; resistant infants are distressed and cannot be soothed; disorganised infants show no coherent strategy — none matches the quick comforting described.

  11. A child says that one should not steal 'because you would get caught and be punished for it'. In Kohlberg's theory, this reasoning belongs to which level?

    1. Conventional morality, reasoning from society's laws and the need to maintain the social order
    2. Postconventional morality, reasoning from a freely chosen social contract agreed among people
    3. Preconventional morality, reasoning from the avoidance of punishment and obedience to power
    4. Postconventional morality, reasoning from self-chosen universal ethical principles of justice
    Show answer

    Answer: C — Preconventional morality, reasoning from the avoidance of punishment and obedience to power

    Reasoning from fear of punishment is the punishment-and-obedience orientation of the preconventional level, where morality turns on consequences to the self. Appeal to law-and-order is conventional; appeals to a social contract or to universal principles are the two postconventional stages, all of which go beyond simple fear of being caught.

  12. In a version of Piaget's classic story pair, a child hears of John, who accidentally breaks fifteen cups while coming in to help at dinner, and of Henry, who breaks one cup while trying to steal jam. A young child says John is the naughtier because he broke more cups. In Piaget's account of moral judgement, this reasoning is characteristic of:

    1. Autonomous morality, because the child weighs the intentions of the actors and treats rules as changeable agreements
    2. Formal operational reasoning, because the child reasons abstractly about hypothetical moral principles
    3. Heteronomous morality, because the child judges wrongness by the size of the damage rather than by the intention behind it
    4. Postconventional morality, because the child appeals to universal ethical principles that stand above particular laws
    Show answer

    Answer: C — Heteronomous morality, because the child judges wrongness by the size of the damage rather than by the intention behind it

    Judging by the amount of damage and ignoring intention is Piaget's heteronomous morality (moral realism), typical of younger children. Weighing intentions and seeing rules as changeable agreements marks autonomous morality, which comes later; this child does neither. Abstract reasoning about principles is formal operational thought, and postconventional morality is Kohlberg's, not Piaget's, scheme, so neither fits a young child focused on broken cups.

  13. Socioemotional selectivity theory (Carstensen) explains why many older adults deliberately narrow their social circles to a few close, emotionally meaningful relationships. Its core proposal is that:

    1. Older adults inevitably and mutually withdraw from society in a process the theory treats as natural and functional
    2. Well-being in old age depends chiefly on staying as active and as socially involved as a person was in middle age, keeping up the same roles
    3. Ageing is caused mainly by the gradual accumulation of oxidative free-radical damage to the body's cells over a lifetime, until normal function can no longer be kept up
    4. As the time left in life is perceived as limited, people increasingly prioritise emotionally meaningful goals over information-seeking ones
    Show answer

    Answer: D — As the time left in life is perceived as limited, people increasingly prioritise emotionally meaningful goals over information-seeking ones

    Socioemotional selectivity theory ties the narrowing of social networks to a shifting time horizon: when time feels limited, emotionally meaningful goals win out over information-gathering ones. Mutual withdrawal is disengagement theory; staying active is activity theory; free-radical damage is a biological theory of ageing, not an account of social motivation.

  14. Consider these statements about the biological basis of development, labelled P, Q, R and S. Which are correct?
    P: A gene is a segment of DNA that carries the instructions for building a protein.
    Q: In humans, biological sex is typically determined by the pattern of the sex chromosomes, XX or XY.
    R: The heritability of a trait tells us what proportion of a single individual's trait was produced by their genes.
    S: Twin and adoption studies are used to estimate the relative contributions of heredity and environment.

    1. P
    2. Q
    3. R
    4. S
    Show answer

    Answer: A — P; B — Q; D — S

    P, Q and S are correct. R is false: heritability is a population statistic about the share of variation between people linked to genes, not a statement about the make-up of any one individual's trait. P defines a gene, Q states sex determination, and S names the standard methods for the nature-nurture question.

  15. Consider these statements about Piaget's stages of cognitive development, labelled P, Q, R and S. Which are correct?
    P: In the sensorimotor stage the infant achieves object permanence.
    Q: Egocentrism and the failure of conservation are characteristic of the preoperational stage.
    R: The ability to reason logically about concrete, tangible problems marks the concrete operational stage.
    S: Abstract and hypothetical reasoning is already fully present in the preoperational stage.

    1. P
    2. Q
    3. R
    4. S
    Show answer

    Answer: A — P; B — Q; C — R

    P, Q and R are correct. S is false: abstract and hypothetical reasoning belongs to the formal operational stage, not the preoperational one, where thought is still tied to appearances. P, Q and R each correctly match a hallmark to its stage.

  16. Consider these statements about Erikson's theory and about attachment, labelled P, Q, R and S. Which are correct?
    P: Each of Erikson's stages centres on a psychosocial crisis whose resolution shapes later development.
    Q: The first crisis, in infancy, is trust versus mistrust.
    R: In Erikson's scheme, generativity versus stagnation is the central crisis of adolescence.
    S: Bowlby argued that infants are biologically predisposed to form an attachment to a caregiver.

    1. P
    2. Q
    3. R
    4. S
    Show answer

    Answer: A — P; B — Q; D — S

    P, Q and S are correct. R is false: generativity versus stagnation is the crisis of middle adulthood, while adolescence is identity versus role confusion. P describes Erikson's crisis structure, Q names the infant stage, and S states Bowlby's biological view of attachment.

  17. Consider these statements about theories of ageing, labelled P, Q, R and S. Which are correct?
    P: Programmed theories treat ageing as following an internal biological timetable or clock.
    Q: Damage or error theories attribute ageing to the accumulation of cellular damage, such as from free radicals.
    R: Disengagement theory holds that older adults and society tend to withdraw mutually from each other.
    S: Activity theory holds that well-being in later life depends on withdrawing from social roles and activity.

    1. P
    2. Q
    3. R
    4. S
    Show answer

    Answer: A — P; B — Q; C — R

    P, Q and R are correct. S is false and inverts activity theory, which holds that well-being depends on staying active and engaged, not on withdrawing. P and Q correctly contrast the two families of biological theory, and R correctly states disengagement theory.

  18. Kohlberg's theory of moral development is organised into 3 broad levels, and each level contains 2 stages. How many distinct stages does the full theory describe in total? Give your answer as a whole number.

    Numerical answer — type the value.

    Show answer

    Answer: 6

    Three levels (preconventional, conventional, postconventional) with two stages each give 3 x 2 = 6 stages in all: punishment-and-obedience, instrumental exchange, interpersonal approval, law-and-order, social contract, and universal ethical principles.