“The process of growth and differentiation”

Development refers to the progressive changes in size, shape, and function during the life of an organism by which its genetic potentials (genotype) are translated into functioning mature systems (phenotype). Most modern philosophical outlooks would consider that development of some kind or other characterizes all things, in both the physical and biological worlds.

Developmental Psychology

The branch of psychology that studies how growth and physiological/ psychological/ social changes take place over the life span Also called Life-span Psychology, it is concerned with the changes in cognitive, motivational, psycho-physiological, and social functioning that occur throughout the human life span. During the 19th and early 20th centuries, developmental psychologists were concerned primarily with child psychology.

Human Development

  • Biological sense: progressive change in size, shape, and function, of the body during the life span; the genetic potentials are translated into functioning adult systems
  • Psychological sense: the ways by which physical, cognitive and psychosocial characteristics change over life span; such development is complex, systematic, and age- related
  • Developmental changes can be quantitative and easy to measure such as height and weight and the expansion of vocabulary
  • Developmental changes can be qualitative i.e., changes in kinds that are more complex and involve “leaps” in functioning. these distinguish a crawling baby from a walking child, a nonverbal child from a talking child, self- absorbed adolescent from a mature adult

Psychological changes include the growth of:

  • Learning
  • Cognition
  • Intelligence
  • Emotional maturity
  • Creativity
  • Sociability
  • Morality…and much more These small leaps are based upon small series of steps that we continue to take throughout our life span

Issues of Interest to Developmental Psychologists

Is development continuous or discontinuous?

Some psychologists believed that human functioning does not undergo fundamental changes but instead changes gradually in its efficiency and working capacity; initially a child spoke a few words but gradually these words become longer and more complicated, increasing the child’s ability to remember and use them in sentences. Other psychologists maintain that changes in development reflect psychological processes that mediate human functioning. These are qualitatively unique stages, in which the evolution of one stage may depend on the traits of the preceding stages. e.g. Roger Brown, psychologist, maintains that in the process of language acquisition, a child progresses systematically in five steps or stages. Each stage has its own set of rules and skills from which a higher level of language acquisition takes place.

Jean Piaget maintained that cognitive development occurs in a series of steps in which the child acquires and uses unique sets of cognitive processes that allow the child to think in identifiable ways.

Is development general or specific?

  • Many aspects of functioning show simultaneous changes; a co-occurrence of change in different situations.
  • Changes occur in specific areas of functioning that do not occur in other level of functioning.
  • Development may remain isolated in specific domains.e.g. Video game mastery in young boys

Is development stable or changing?

In some respects development is stable and stays there for very long, whereas in some ways it keeps moving. Temporal aspect: degree of stability or change across the lifespan Situational aspect: degree of stability or change across a wide variety of experiences.e.g. Aggressive behavior in children

Humans active or passive beings?

Psychologists maintain that humans are active recipients as well as participants in their course of development. Man seeks to understand the strategies that he can adopt in order to influence development Jean Piaget emphasized the active participation of the child in acquiring cognitive skills__ acquisition of knowledge and ability to use it effectively. Some philosophers believed that humans are passive beings whose development is entirely dependent on the environmental stimuli/ forces. These conditions may be internal i.e. food, water, companionship etc or external i.e. previously experienced reward or punishment These psychologists tend to view differences in the patterns of development in which an individual is exposed to different environmental situations

Nature versus Nurture

  • Nature means hereditary influences.
  • Nurture refers to environmental influences, in child development.
  • Once, it was assumed that these were significant forces that operated independently of each other.
  • In the 17th century the French philosopher René Descartes set out views which held that people possess certain inborn ideas that are long lasting and color people’s approach to the world.
  • The British philosophers Thomas Hobbes and John Locke, on the other hand, took a more empirical approach and emphasized the role of experience as fully contributing to behavioral development.
  • Since the days of Descates, Hobbes, and Locke, the empirical “nature” approach has led to a lot of debate; many followers and many opponents.
  • Mid to late 1800′s, through to the early 1900′s the nature approach was the sole standpoint; consistent with the scientific discoveries of the role of inheritance and natural selection by Mendel and Darwin
  • The psychological argument developed later; Francis Galton “Hereditary Genius” (1869); “gifted individuals” tended to come from families, which had other gifted individuals. He went on to analyze biographical dictionaries and encyclopedias, and became convinced that talent in science, professions, and the arts, ran in families.
  • Galton went even further arguing that it would be “quite practicable to produce a high gifted race of men by judicious marriages during several consecutive generations”.
  • Eugenics: “the study of the agencies under social control that may improve or repair the racial qualities of future generations, either physically or mentally.”

For Galton

  • “What Nature does blindly, slowly, and ruthlessly, man may do providently, quickly, and kindly”
  • “Intelligence must be bred, not trained”.
  • Such arguments have had massive social consequences and have been used to support apartheid policies, sterilization programs, and other acts of withholding basic human rights from minority groups

The later scientists, especially the behaviorists contested such an approach and advocated the role and significance of environmental influences

Prevalent Approach

  • Both influences are essential and are mutually influential. The role of interaction between heredity and environment together is important. e.g., how a child responds to parenting—an environmental influence—is partly determined by the child’s temperament and other inherited characteristics.
  • The environment influences how hereditary characteristics develop and are expressed e.g. increase in average height during the last century because of improved nutrition and medical care.
  • Even though many features of personality are based on inherited temperament, the family environment is an important influence on a child’s personality development.
  • A child with a difficult or unpredictable temperament can develop positively in a warm and loving family environment.
  • Intelligence is an inherited feature but the way it is utilized largely depends on the environmental conditions.

Characteristics with Strong Genetic Components

  • Physical Characteristics
  • Intellectual Characteristics
  • Emotional Characteristics and Disorders

Physical Characteristics

  • Height
  • Weight
  • Obesity
  • Tone of voice
  • Blood Pressure
  • Tooth decay
  • Athletic ability
  • Firmness of hand shake
  • Age of death
  • Activity level

Intellectual Characteristics

  • Memory
  • Ability as measured on intelligence test
  • Age of language acquisition
  • Reading disability
  • Mental retardation

Emotional Characteristics and Disorders

  • Shyness
  • Extraversion
  • Emotionality
  • Neuroticism
  • Schizophrenia
  • Anxiety
  • Alcoholism

Prenatal Environmental Influences

  • Mother’s nutrition and emotional state
  • Illness of mother
  • Mother’s use of drugs
  • Birth complications

Studies to Determine the Relative Importance of Nature or Nurture

i. Twin Studies

  • Studies making use of twins, identical or fraternal…reared apart and reared together
  • The case of Gerald Levey and Mark Newman, twins reared apart, who had not seen each other before: When method, both were bald, 6 and a half feet tall, volunteer fire fighters, 250 pounds in weight, had droopy moustaches, wearing key rings on right side of their belts, liked to wear aviator style dark glasses; both had interest in similar subjects, had jobs in the supermarket, and liked tall, slender women with long hair; had similar hobbies, liked Chinese food and same drinks; showed similar mannerism, laugh similarly, and loved to fight fire

Twin Studies with Monozygotic Twins

i.Twin Studies with Monozygotic Twins

ii.Twin Studies with Dizygotic Twins

a.Twins reared apart: Different genes-different environment

b.Twins reared together: Different genes-same environment

i.Adoption Studies

Twin Studies with Dizygotic Twins




Children with different sets of genes, brought up by same parents…in same environment.

ii. Consanguinity Studies

Study of as many blood relatives as possible of a particular family; these study the extent to which certain features/ characteristics are shared.

iii. Selective Breeding of Traits in Animals

Certain characteristics are cultivated in animals (running in a maze, aggression, obesity etc) and if it is transmitted on to the next generation then that trait is partly inherited. These findings are then generalized to humans…. although its validity is doubtful

Research on Nature- Nurture, Focusing on Environmental Issues

  • Research looking for possible environmental causes for certain traits/ behaviors
  • These include prenatal studies, and studies involving manipulation of the environmental factors e.g. nutrition, exercise, drugs, pollution etc
  • These involve comparing actual history: surveys etc. •

Limitations of Nature-Nurture Research

  1. Ethical considerations in research with humans
  2. Not all animal research can be applied to humans

The best solution probably is the ex-post facto/ retrospective studies

Heredity and Physical Development

Researchers believe that although environment exerts an important influence on human development, physical traits are the ones more evidently influenced by heredity. Personality and intellectual characteristics are also affected by it

Mechanism of Heredity: Transmission of Genetic Characteristics

The process begins from the moment of conception; a sperm from the father unites with the ovum/ egg of the mother to form zygote, a single-cell/one-celled product, containing the complete genetic package for the one to be born much later

The zygote contains 23 pairs of chromosomes


  • Each sperm and ovum contains 23 chromosomes that are tiny rod- shaped particles containing genetic/ heredity information.
  • Genetic/ heredity information is packed in the genes.
  • Genes: parts of chromosome that are the transmitters of inheritance.
  • Genes produce particular characteristics of the new being, either individually or in combination

Genes may be dominant or recessive; a dominant gene means that its characteristics will dominate those of the recessive one e.g. if father has brown eyes and mother has black eyes, and if the father’s genes dominate then the baby will have brown eyes.

o Each zygote’s 46 chromosomes contain about 30,000 segments strung along its


beads i.e., “genes” Genes, made up of Deoxyribonucleic Acid (DNA,) determine all our heredity

Prenatal Stages

EMBRYO: A developed zygote with a heart, a brain and other organs.

Fetus: A developing child; 9 weeks after conception till birth.

Determination of the Sex of the Embryo

  • A combination of chromosomes from the parents determines sex.
  • An XX pair means a female will be born An XY pair means a male will be born.
  • The mother’s sex chromosome is always and ‘X’ but the father may be either ‘X’ or ‘Y’. If X chromosome is being contributed by the father’s side then the new being has to be a female; and if the father is contributing a ‘Y’ chromosome then the new being is going to be a male

Genotype and Phenotype

  • Genotype: genetic composition of a person.
  • Phenotype: observable characteristics.
  • The characteristics that can be observed and seen, make up our “phenotype”. They may not always be the same e.g. person may have brown eyes (phenotype) but carry genes for both brown and blue eyes (genotype) __ dominant gene is brown


o This difference in color is due to the fact that genes come in alternative forms called “Alleles” (alternative forms of a gene). When alleles are identical, a person is homozygous for a trait; when alleles are dissimilar the person is heterozygous

Patterns of Transmission of Characteristics

i. Homozygous and Heterozygous

When the person inherits identical alleles he is said to be “homozygous” (possessing two identical alleles for a trait). When he inherits two different alleles then the person is “heterozygous” (possessing two different alleles for a trait).

Example: when a person is homozygous for brown eyes then he will transmit only genes for brown eyes to his offspring and if heterozygous for blue and brown eyes then although dominant one is brown, but he will transfer his both alleles to his offspring.

a. Autosomal Dominant Inheritance

  • Patterns of inheritance in which a specific gene is dominant; if it is inherited; it manifests itself in the person.
  • Autosomal Recessive Inheritance
  • Patterns of inheritance in which trait appears only if a person inherits two genes for it, one from each parent. If the person inherits only one gene for a trait, it will not appear in a person but may be passed on to his children.

ii. Multi- Factorial Inheritance

  • Patterns of inheritance in which a trait is expressed either by a combination of several genes or through the interaction of genes with environmental factors.
  • More complicated combination of genes or an interaction between genetic predispositions and environmental factors that bring them out.
  • Some characteristics follows one of these patterns, other genes another.


Hair type (curly or straight) is either autosomal dominant or autosomal recessive, baldness is sex- linked; height and weight are probably multi- factorial. Some diseases and birth defect are inherited according to these patterns. Most prominent examples are:

Achondroplasia: a kind of dwarfism that is inherited by autosomal dominance.

Tay- Sachs disease: body’s inability to break down fat; results into death by 3-4 years of age

Huntington’s disease: 99.9% correlation between having the identified gene and the disease.

The blood- clotting disorder hemophilia is a sex- linked condition.

Spina bifida: a defect in the closure of the vertebral canal, that is believed to be the condition transmitted by sex- linked inheritance

The process of development continues throughout the life span

While considering aspects of development, individuality and interactions are the key terms in understanding it. All beings bring their unique genetic package into this world and have unique sets of experiences too. An individual’s strengths, abilities, and predispositions are affected by the influence of environment. These influences make a person act in ways that elicit new experiences

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