Source: Comprehensive Overview of Human Development Across the Lifespan
Tags: developmental psychology, nature vs nurture, prenatal development, zygote, embryo, fetus, teratogens, newborn reflexes, brain plasticity, neural pruning, motor development, maturation, lifespan development
Difficulty: Introductory | Prerequisites: None. This is foundational material for the developmental psychology unit.
Developmental psychology covers the entire arc of human change, from conception through to death. This first set of notes deals with the groundwork: the debates that frame the field (nature vs nurture, continuity vs stages), what happens before birth, and how the brain and body develop in infancy and early childhood. If you understand these foundations, the cognitive and social material in Parts 2 and 3 will make far more sense. You do not need any prior psychology knowledge here.
Human development is shaped by the interplay of genetics and environment, unfolds both gradually and in distinct stages, and begins well before birth. Infants arrive with built-in reflexes and a brain that is remarkably plastic, rewiring itself in response to experience throughout early life.
Developmental psychology
The scientific study of how individuals change physically, cognitively, emotionally, and socially from conception to death. In simple terms, it is the study of how and why people change as they age.
Nature
The contribution of genetic inheritance and biological predispositions to development. Think of it as the blueprint you are born with.
Nurture
The contribution of environmental experiences, learning, and culture to development. Think of it as everything that happens to you after (and during) conception.
Continuity theory
The view that development is a gradual, cumulative process, with skills building incrementally over time. In simple terms, growth is like a smooth ramp rather than a staircase.
Stage theory
The view that development occurs in distinct, qualitatively different phases, each with its own milestones and patterns. In simple terms, growth is like climbing steps, where each step is a new kind of ability.
Temperament
A person's characteristic emotional reactivity and self-regulation tendencies. Think of it as your built-in emotional thermostat, partly inherited, partly shaped by experience.
Zygote
The fertilised egg, from conception through approximately the first two weeks. It undergoes rapid cell division and forms a blastocyst that implants in the uterine wall.
Embryo
The developing human organism from about 2 weeks to 2 months after fertilisation. This is when major organs and body structures begin to form.
Fetus
The developing human organism from 9 weeks after fertilisation until birth. Organs, bones, and tissues continue to grow and mature during this period.
Placenta
The organ that transfers nutrients and oxygen from the mother to the developing fetus. Think of it as the life-support system connecting mother and child before birth.
Rooting reflex
An involuntary response where the newborn turns its head towards a touch on the cheek. It aids breastfeeding by helping the infant find the nipple.
Sucking reflex
An automatic response where the newborn sucks on objects near the mouth. It supports nourishment from birth.
Stepping reflex
An involuntary walking motion the newborn makes when held upright. It disappears within a few months and is not the same as intentional walking.
Grasping reflex
An automatic response where the newborn closes its fingers around an object placed in the hand. In simple terms, it is the reason a baby can grip your finger surprisingly tightly.
Neural pruning
The process by which the brain eliminates unused neural connections to optimise efficiency. Think of it as the brain trimming back overgrown wiring so the important circuits work better.
Plasticity (brain)
The brain's ability to adapt its structure and function in response to experience. In simple terms, the brain can rewire itself, and this capacity is especially strong in early life.
Maturation
The biologically driven sequence of growth and development that enables new abilities. Think of it as the internal timetable your body follows regardless of practice or training.
Cerebellum
The brain region at the back of the skull responsible for coordinating movement, balance, and motor learning. Its rapid development around age one is closely linked to the onset of walking.
Development results from the interplay of genetic inheritance (nature) and environmental experience (nurture), not from one or the other alone.
Genes provide biological predispositions, but gene expression can be influenced by environment, learning, and experience.
Example: a child may inherit a tendency towards shyness, but supportive parenting or social opportunities can modify that tendency over time.
The relative influence of nature and nurture can shift across situations and across the lifespan.
In some domains (e.g. eye colour), genetics dominate.
In others (e.g. language spoken), environment is decisive.
The modern consensus is that development is a continuous exchange between the two, not a competition.
Continuity perspective: development is smooth and cumulative, like pouring water into a glass.
Stage perspective: development proceeds in qualitatively different steps, each with unique characteristics.
The evidence supports both views, depending on the domain.
Some abilities (e.g. vocabulary size) grow continuously.
Others (e.g. language acquisition, moral reasoning) appear to progress through clear stages.
Exams frequently ask you to distinguish these two perspectives and give examples of each.
Some traits show remarkable stability across the lifespan.
Temperament (emotional reactivity, self-regulation) tends to remain consistent from childhood into adulthood.
Early behavioural patterns can predict later outcomes: children who are cruel to animals may be more likely to show violent behaviour as adults; children with cheerful dispositions tend to have more enduring marriages.
Other traits are malleable, and can shift due to life experience, environment, or deliberate effort.
The key takeaway: we are neither entirely fixed nor endlessly changeable.
Zygote (conception to ~2 weeks): fertilised egg undergoes rapid cell division, forms a blastocyst, implants in the uterine wall.
Embryo (~2 weeks to ~2 months): major organs and structures begin forming. This is a period of high vulnerability to disruption.
Fetus (~9 weeks to birth): continued growth and maturation of organs, bones, and tissues. The placenta supports the fetus by transferring nutrients and oxygen from the mother.
Newborns arrive equipped with automatic reflex responses critical for survival.
Rooting reflex: turns head towards a touch on the cheek (aids breastfeeding).
Sucking reflex: sucks on objects near the mouth (supports nourishment).
Stepping reflex: legs move in a walking motion when held upright.
Grasping reflex: fingers close around objects placed in the hand.
These reflexes are involuntary, present from birth, and serve as the foundation for early interaction with the environment.
The brain is highly immature at birth but develops rapidly in the first years of life.
Prenatal neural growth: explosive expansion of neural networks occurs before birth.
Postnatal branching: neural connections increase dramatically after birth, especially in the frontal lobes (responsible for reasoning, planning, self-control).
Neural pruning: the brain eliminates unused connections, making the remaining circuits more efficient. This is a "use it or lose it" process.
Plasticity: the brain adapts its structure in response to experience. Critical periods are windows where the brain is especially sensitive to environmental input.
Rosenzweig and Krech's research: rats raised in enriched environments (with toys, stimulation, social interaction) developed larger and more complex brains than those raised in deprived settings. This demonstrates the bidirectional relationship between experience and brain architecture.
Motor skills develop in a predictable, biologically driven sequence.
Rolling over comes before sitting unsupported.
Crawling comes before walking.
Blind children follow the same sequence, confirming that motor development is rooted in neural maturation rather than imitation.
The cerebellum matures rapidly around age one, enabling walking and other complex motor skills.
Physical development also includes gradual control over bowel and bladder function, which depends on muscular and neural maturation. Toilet training cannot be meaningfully rushed; it requires the child's physical readiness.
Enriched early environments (responsive caregiving, stimulation, social interaction) support stronger brain development. This is why early childhood programmes and quality childcare are considered so important for long-term outcomes.
The motor development sequence is used by paediatricians as a benchmark to track whether a child's physical development is on track. Delays in reaching milestones can signal the need for early intervention.
"Nature vs nurture is an either/or question." It is not. Nearly all developmental outcomes reflect both genetic and environmental contributions working together.
"Stage theories mean everyone hits the same milestones at exactly the same age." The sequence is predictable, but the timing varies between individuals.
"Newborn reflexes are useless leftovers." They are functional survival mechanisms that also promote early learning and bonding.
"Brain development is finished by birth." The brain is far from finished at birth. Massive growth, branching, and pruning continue well into childhood and beyond.
⚠️ Be able to explain the nature-nurture interaction with a specific example (e.g. temperament shaped by parenting).
⚠️ Know the difference between continuity and stage theories, and be able to give an example of each.
⚠️ Memorise the three prenatal stages (zygote, embryo, fetus) and their approximate timelines.
⚠️ Be able to name and describe all four newborn reflexes.
⚠️ Understand what neural pruning is and why it matters.
⚠️ Know the Rosenzweig and Krech enriched-environment study and what it demonstrated.
True or false: Development is determined entirely by genetics. ___
The prenatal stage from 9 weeks to birth is called the ___.
True or false: Blind children follow a different motor development sequence from sighted children. ___
The process by which the brain eliminates unused connections is called ___.
True or false: The continuity view of development says growth happens in distinct, separate stages. ___
Answers: 1. False. 2. Fetus. 3. False (they follow the same sequence). 4. Neural pruning. 5. False (that describes the stage view).
Q: What is the nature-nurture interaction in developmental psychology?
A: Development results from the continuous interplay between genetic inheritance (nature) and environmental experiences (nurture). Neither alone determines outcomes; gene expression is influenced by environment, and environmental effects depend partly on genetic predispositions.
Q: Name the three stages of prenatal development and give the approximate time frame for each.
A: Zygote (conception to ~2 weeks), embryo (~2 weeks to ~2 months), fetus (~9 weeks to birth).
Q: What did Rosenzweig and Krech's research with rats demonstrate about brain development?
A: Rats raised in enriched environments (with toys, stimulation, and social interaction) developed larger and more complex brains than rats raised in deprived settings. This showed that experience directly shapes brain architecture.
Q: List the four newborn reflexes and briefly describe each.
A: Rooting (turns head towards touch on cheek), sucking (sucks on objects near mouth), stepping (walking motion when held upright), grasping (closes fingers around objects in hand).
Q: How does the concept of neural pruning relate to the phrase "use it or lose it"?
A: Neural pruning eliminates neural connections that are not regularly used, strengthening the remaining active circuits. Connections that are stimulated through experience are retained; those that are not are pruned away.
This material connects directly to Piaget's cognitive development stages (Part 2), since cognitive growth depends on the brain maturation covered here. The nature-nurture debate also reappears in discussions of attachment styles and parenting (Part 2), and again when considering cognitive decline in ageing (Part 3).
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