PHYSICAL DEVELOPMENT AND NATURE NURTURE ISSUE:Nature versus Nurture

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Introduction to Psychology PSY101

Lesson 10

PHYSICAL DEVELOPMENT AND NATURE NURTURE ISSUE

Development

"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 non-

verbal 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.

Introduction to Psychology PSY101

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".

Introduction to Psychology PSY101

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

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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

Twins reared apart: Same genes-different environment

ii.

Twins reared together: Same genes-same environment

Twins reared

Apart

Twin Studies with Monozygotic Twins

Twins reared

Together

Twins reared

Apart

Reared together:

Same genes-same

environment

Monozygoti

c Twins

Twin Studies with Dizygotic Twins

a. Twins reared apart: Different genes-different environment

b. Twins reared together: Different genes-same environment

Twin Studies with Dizygotic Twins

Twins Reared

Together

Apart

Reared apart:

Reared together:

Different genes-

Different genes-same

different environment

environment

Fraternal/ Dizygotic

Twins

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i. Adoption Studies

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

o Ethical considerations in research with humans

o 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

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

Introduction to Psychology PSY101

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

Alleles

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.

b. 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.

Introduction to Psychology PSY101

Examples

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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