THE RELATIONSHIP BETWEEN GROWTH AND DEVELOPMENT

After going through the meaning and concept of growth and development as well as the different theories of development, now we are going to identify the relationship between the two, which are as follows:

The term growth is used in purely physical sense. It generally refers to an increase in size, length, height and weight. Changes in the quantitative aspects come into the domain of growth. Development implies overall changes in shape, form or structure resulting in improved working or functioning. It indicates the changes in the quality or character rather than in quantitative aspects.

Growth is one of the parts of developmental process. In a strict sense, development in its quantitative aspect is termed as growth. Development is a wider and comprehensive term. It refers to overall changes in the individual.

Growth describes the changes which take place in particular aspects of the body and behaviour of an organism. Development describes the changes in the organism as a whole and does not list the changes in parts.

Growth does not continue throughout life. It stops when maturity has been attained. Development is a continuous process. It goes from womb to tomb. It does not end with the attainment of maturity, the changes however small they may be, continue throughout the life span of an individual.

THE PRINCIPLE AND FACTOR OF GROWTH AND DEVELOPMENT

Each child’s path or pattern of growth and development is determined by genetic and environmental factors. 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.

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 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 genes 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 this Table.

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.