Each child’s path or pattern of growth and development is determined by genetic and environmental factors. These are known as factors of growth and Development. The genetic factors determine the potential and limitations of growth and development.
If favourable, the environmental factors, such as adequate nutrition, facilitate the achievement of the genetic potential of growth and development. Unfavourable factors, acting singly or in combination, slow or stop growth and development. Some of the unfavourable factors are malnutrition, infections, congenital malformations, hormonal disturbances, disability, lack of emotional support, lack of play, and lack of language training.
To promote optimum growth, these environmental factors can be removed or minimised. Once they are removed, there follows a period of catch-up growth. During this period the growth rate is greater than normal. This growth rate continues until the previous growth pattern is reached. Then the growth rate is reduced to the normal rate determined by the individual’s genetic factors.
A child genetically determined to be tall grows slightly more rapidly than a child genetically determined to be short. Similarly, a child genetically determined to be clever develops their intellect more rapidly than a child genetically determined to be less intelligent. Let us now take a look at how factors such as heredity and environment act to command growth and development of a human being.
2.1.1 HEREDITY
All species
transmit characteristics from one generation to the other through the mechanism
of genetics. It implies that every human being carries genetic traits that one
inherits from their parents. This implies that each of us has a genetic code
that we inherited from our parents which is located within every cell in our
body. It is because of the human genetic code that a fertilised human egg
cannot grow into a sheep, hen, goat, cow or fish. Heredity therefore is the
transmission of traits from one generation to the other.
The genetic
instructions come about as a result of a single cell that is formed after
fertilisation has taken place. The single cell is responsible for housing the
entire genetic code. The single cell later on grows into a person made of
trillions of cells, which contain a perfect replica of the original genetic
code. The nucleus of each human cell contains 46 chromosomes, which are thread
like structures that are 23 pairs. Each parent therefore contributes 23
chromosomes. Chromosomes consist of an important genetic substance called
deoxyribonucleic acid (DNA) with associated molecules that have genetic
information. Genes, which are units of hereditary information, are segments of
the DNA in a chromosome. This implies that DNA is made up of genes. Genes act
as a blueprint for cells to reproduce and manufacture proteins that are
necessary to sustain life.
Gametes are
the human reproductive cells that are created in the testes of males and
ovaries of females. The male gametes contain XY chromosomes while female
gametes contain XX chromosomes. Meiosis is the process of cell division in
which sperm and ova are formed whereby the number of chromosomes in both cells
of an organism is halved with one member of each pair going into each daughter
cell hence each human gamete has 23 unpaired chromosomes. Reproduction comes
about when a male gamete (sperm) fertilises a female gamete (ovum) resulting into
what is called zygote. It is therefore a common knowledge that a zygote
contains two sets of unpaired chromosomes, which combine to form a set of
paired chromosomes.
One member
of each pair comes from either of the parents. Thus each parent contributes 50%
of the offspring’s chromosomes.
The laws of inheritance
The basic
laws of inheritance or genetics are associated with Gregory Mendel. Mendel was
a Monk who opted to be a teacher but because he failed his exams due to lack of
insight and the requisite clarity of knowledge, he went back to his monastery
and devoted most of his life to study plants. It was thought at this time that
while a child would inherit his father’s hair colour, or his mother’s eyes
colour or any other feature, the general pattern of inheritance was a blending
of family characteristics. Mendel contributed to the study of genetics by
formulating two cardinal laws. The first law states that genes do not blend but
they separate. Given the fact that genes are always in pairs, then in Mendel’s
views there are two possible course of action.
a.
If both genes are the same, then the offspring will be born with those
characteristics or features
b.
If the genes are different, then one gene becomes dominant
The loss or
gain of genes is determined by either dominant or recessive genes in which case
the dominant always wins. However, the recessive genes may stay in the cell and
when given a chance, then they may manifest on the subsequent generations. This
is precisely why a particular characteristic can remain within a family for
several generations before it appears. For instance, brown eyes are dominant
and grey eyes are recessive. Therefore, if a brown-eye gene crossed with a
grey-eye one, then the offspring will have brown eyes but the brown eyed person
will carry the grey-eye gene.
If such an
individual mates with another person who also carries a grey-eye gene, then the
two recessive genes have a higher probability of meeting. Consequently, their
offspring will have grey eyes. This implies two brown-eyed people will have a
grey-eyed offspring. Some features of an offspring are carried on X chromosomes
and are known as sex- linked. The most well-known such characteristics are
colour blindness and haemophilia (a state in which bleeding never stops naturally).
It has been revealed that more males are colour blind than their female
counterparts because females always inherit two chromosomes and so they have
colour blindness gene cancelled out by one from the other chromosome.
Mendel’s
second law of inheritance is that of the ratios of inherited characteristics.
Let us go back to brown and grey eyes, we can assume that there are 8 people,
each with a brown and a grey-eye gene give birth to 4 children. Mendel’s law
holds that the likelihood of a child being born with grey eyes is one in four
as depicted in Table 3.2.
|
Genes |
Mr. A Brown Grey |
Mrs. A Brown Grey |
Mr. B Brown Grey |
Mrs. B Brown Grey |
Mr. C Brown Grey |
Mrs. C Brown Grey |
Mr. D Brown Grey |
Mrs. D Brown Grey |
|
Passed on
: raid’s eyes colour |
BB Brown |
gg Grey |
Bg Brown |
gB Brown |
||||
Table 1:
Showing Mendel’s Second Law
Only one
child of Mrs. B and Mr B has grey eyes because he inherited two recessive genes
from the parents. The implication here is that the recessive genes have an
equal chance of being inherited only when both have entered a cell.
However,
the critics of Mendel’s law given above are of the view that some
characteristics or features are observable blends such as skin colour. This is
contrary to Mendel’s view that genes do not blend.
The critics
suggest that not all characteristics are got from a single gene, some involve
two or more. For instance, first generation of a black-white couple will be an
intermediate colour. If the family inter-bred, the resulting sixteen
grandchildren are likely to be: one black, one white, four dark, four light,
and six in between.
Influence of heredity on human behaviour
The
following are some of the inherited behaviours:
Inherited smell difference
People tend
to differ in their abilities to smell certain odours. The differences range all
the way from person without any sense of small (anosmia) to those who have.
For
instance, some people deny that freesia, a kind of a flower has any flagrance,
and others say that it has a pleasant odour while others claim that it stinks.
Trisomy D and E
Trisomy D
involves an extra pair of chromosomes on the 13th, 14th and 15th chromosomes.
This kind of inheritance is characterised by deficient forebrain development,
which contributes to emotion, consciousness and planning. This leads to
learning disabilities and poor social skills. It also leads to the absence of
olfactory tract (in cases of nasal passages), presence of small eyes or no eyes
and severe mental retardation. On the other hand, Trisomy E involves cardiac
and kidney defects and hypertonicity.
Cri-du-chat
This is
caused by lack of one part of the chromosomes pair number 5, which results in
mental retardation. Children who have this defect cry in a similar way to a cat
or kitten.
Sex-chromosome
trisomy i.e. Klinefelter’s syndrome, sex chromosome trisomy XYY, sex chromosome
monosomy, i.e. Turner’s syndrome, autosomal trisomy i.e. mongolism,
phenylketonuria etc. are the other types of inheritable abnormalities.
Heredity
alone does not act solely to determine the way development takes place in an
individual. Environment is also an important factor in development. Its effect
is realised immediately one comes into the world. Environmental factors such as
home, school, church, playmates or peers are quite influential in determining
the way one behaves or develops. We will see how this occurs in the next
section.
INFLUENCE OF ENVIRONMENT ON DEVELOPMENT
Many
phenotype factors in human beings are genetically transferred from parents to
offspring. However, people who live in a particular place express similar
traits. This is because of the environmental situations they are exposed to.
For instance, for Tchumali people, women do heavy work such as constructing
houses, splitting fire wood which has made them develop more masculine bodies
than their male counterparts who do light work. The role of the environment
impacting on individual’s behaviour can be seen in its effects on pre-natal and
postnatal developments. Environment begins to affect an organism as soon as
conception takes place. Some traits of the offspring may be traced back to
earlier stages of development and having been brought about by environmental
effects, for instance injection of male sex hormone in a pregnant mother of a
female foetus will cause it to have a male brain.
Effects of
growth and mental development are commonly noticeable, which may be facilitated
by factors present in an environment as well as inherited. For instance, the
average I.Q for underprivileged children are much below than that of privileged
ones. This is because the underprivileged are greatly retarded in skills, which
have been made available to the privileged ones in a more favourable
environment. Besides, body development traits such as body physique can be
caused by the environment in which one operates, for instance, heavy work,
exercise and the kind of food one eats. When these are not favourable then it
may lead to the growth of different traits and physique.
An
individual’s personality may be inherited or facilitated by the environment.
The effect of culture upon attitudes, ideas and behavioural patterns of an
individual have been clearly shown. For instance, it has been observed that
children brought up in a family where parents quarrel or where they are denied
basic essentials and only gain them unfairly leads to children developing
quarrelsome or stealing behaviour in their future lives. Other developmental
patterns are governed by both heredity and environment. It is believed that in
most cases heredity plays a more dominant role in influencing behaviour than
environment, some of the behaviours influenced by both heredity and environment
are as follows:
The athletic genius
World
famous professionals in athletics display unusual abilities at an early age.
They often have a family history of similar achievements.
This is due
to biological inheritance. They inherit the nature of their sensory structure,
which makes possible the heights they obtain, for instance, the Kalenjin
athletes of Kenya. Apart from that, environmental influences also play an
important role in influencing their behaviours. This is evident in family
traditions, early training, expert teaching and higher hopes of getting a job.
In general,
there are various environmental factors that determine human development. These
are:
•
Physical environment: human beings need sufficient food,
air, water and light for proper development. We also need comfortable space for
movement and practice for proper development.
•
Family: usually, it is the fundamental unit
in society. The family helps us learn sex roles, social skills and language.
The patterns of family interaction, family size and quality of attention among
family factors are found to profoundly affect development.
•
Peers: this is where children come under
the influence of others of their own age group. This mostly affects their
development and patterns of responses. These influences continue throughout
life.
•
School: schools influence a person’s
intellect, social skills mental health and other aspects of behaviour through
formal and informal programmes. •
•
Mass media: it is believed that what we read
watch and listen to from newspaper, TV or radio greatly influences our
behaviour and personality, values and expression of emotions. You may find it
useful to revisit the sections on heredity and environment in the previous
Module 1 “Introduction to Psychology”.
RELATIONSHIP BETWEEN NATURE AND NURTURE
Having
learned about how both nature (heredity) and nurture (environment) affects
human behaviour, you should recognise that every trait of an organism depends
on heredity and environment. However, psychological traits such as
intelligence, special talents, emotions and insanity cannot be separated from
those inherited. This notion sheds light on the fact that the nature-nurture
relationship may be conceived in terms of additive contribution whereby both
contribute to all behavioural development. This view is accepted by many people
but it does not hold for all the analyses. For instance, attempts have been
made to determine the above view on intelligence and the results showed that
heredity contributes about 75% and environment 25%.
It should
also be noticed that the extent of influence of each factor, either nature or
nurture, depends on the contribution of the other. For instance, one nurture
factor will exert a different influence depending upon specific materials it
contributes. Similarly, any nature factor will operate differently under
varying environmental conditions. For example, diet and exercises (nurture)
lead to body weight and shape also nature will lead to body weight and shape
due to inherited traits.
Furthermore,
a person’s I.Q (nature) may be retarded by metabolic disorders (nurture), which
is attributed to a single recessive gene. Such intellectual level is determined
largely by heredity, whereas some individual’s I.Q may be below average due to
traceable prenatal cerebral injury. In this case, the level of intelligence
largely depends on environmental factors.
It can be concluded that it is difficult to determine what is contributed by heredity and by environment as far as human development is concerned. However, for most of the characteristics and traits including our body or somatic structure, physical, mental, social and emotional make up, it is the interaction between the individual's genetically determined characteristics and environment which is said to be more responsible for making a person what he/she is.
WHY TEACHERS NEED TO UNDERSTAND HUMAN GROWTH AND DEVELOPMENT
Many
psychologists and educationists have appreciated the value of the knowledge of
growth and development or simply put, developmental psychology to education,
some of the most important contributions are as below:
•
It
helps in understanding how children change as they grow up and the forces that
contribute to this change or make children become maladjusted
•
It
has helped in training early childhood educators who are qualified in early
childhood education with specialisation in day care of children
•
It
helps in training of pre-school teachers who are to take care of
pre-kindergarten children, many of whom are 4 years old. Such teachers are
expected to develop appropriate curricula for the age of the children that
helps in promoting their physical, cognitive and social developments in a
positive atmosphere
•
Helps
in understanding the roots of social difficulties encountered by many of
today’s adolescents, for instance problems that cause them to drop out of
school.
•
It
helps teachers, prospective teachers and parents to be in a position to
understand the individual differences in learning among learners so that they
can be able to adapt their teaching according to the learner’s mental
requirements by using different teaching methods
•
Teachers
and parents get to know the needs and motives of children at different levels
so that they (teachers etc.) can motivate the children accordingly
•
It
enables teachers, psychologists, and parents to understand the mental and
emotional reactions of individual child
•
It
helps psychologists, teachers, development psychologists, etc. to understand
the nature of classroom learning and the learning processes of children in
general.
Furthermore,
the main implications of the growth and development of principles for teaching
and learning processes are as follows:
·
The fact that the
students in the class are at varying levels of growth and development, have
acquired different types of experiences implies that though the same curriculum
is being used, the classroom setting must be appropriate and rich enough to
accommodate these differences. The use of instructional aids of various types
often helps greatly in this situation.
·
Also, the children
are at various levels of developments meaning they cannot all perform the same
developmental tasks. The teaching strategy of the teacher must reflect this in
the classroom otherwise not all the pupils will be carried along. This should
be noted too during skill performance.
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