The Biological Foundations of The Biological Foundations of Development:Development:

The course of physical growth

The course of physical growth.The course of physical growth. Theorists think that the slow course of physical

growth provides us with added time to learn the skills which are required in a social live: Humans have not already depended on his body to survive. We are social animal.

Physical growth are determined by environment. Physical growth doesn´t happen independently of input from the environment. Factors, like nutrition, cultural practices or experience, affect to physical development.

The patterns of growthThe patterns of growth There are two patterns of growth:

◦ Cephalocaudal: The develop happen in a head to toe direction. For example, within the head, eyes and brain grow faster than jaw.

◦ Proximodistal: The develop happen outwards from the centre of the body. For example, baby will acquire control over the muscles of the neck and trunk before it acquires control over the fingers and the toes.

Body sizeBody size

Changes in body size are the most obvious manifestation of physical growth.

In general, physical developments in height and weight tend to occur:

very rapidly in infancy

continue at a steady pace throughout childhood

and then slow down towards puberty

At puberty there is a marked growth spurt, a very rapid increase in size and weight.

This pubertal growth spurt varies from person to person in terms of its intensity, its duration and its age of onset.

It tends to last around 4 ½ years.

In girls, it usually begins around age 11 and boys two years later.

Growth may still take place after the completion of the pubertal spurt

Hereditary factors play a strong role in physical Hereditary factors play a strong role in physical growthgrowth

There is a large and stable correlation in identical twins (the ones who come from the splitting of one fertilized egg)

Fraternal twins (fertilization of two different eggs) have smaller correlations.

This suggest that genetic factors play an important role in determining height

These patterns are observed for weight as well as for the timing of growth spurts

Environmental factors in physical Environmental factors in physical growth: Nutritiongrowth: Nutrition The human physical growth is, as we all know,

controlled by our genetic, but there is another aspects that can influence it, one example is the nutrition, which means:

What do we eat

and

How much do we eat

The studies made during de WW2 showed that the wartime conditions (few food) caused a decrease in the average height and a reverse a trend towards increasing weight since the end of the WW1.

Other problems caused by malnutrition are, for example:

The dietary restrictions had an effect in puberty like, for example, the menarche is delayed by 3 years.

Cognitive development has also been affected:1. Anemia – slowing of intellectual development2. Intestinal worms – stole valuable nutrients for

growth

Environmental factors in physical Environmental factors in physical growth: Hormonal influencegrowth: Hormonal influence

The most important of this glands is the pituitary gland, located near the base of the brain. The pituitary gland, triggers chemical changes.

Via hormones which it secretes to the bloodstream, which act on various tissues and indirectly by triggering other glands to release different hormones.

The pituitary gland also controls the primary sexual characteristics (growth involving the reproductive organs,) and the secondary sexual characteristics ( visible changes which are associated with sexual maturation) due to the segregation of big amounts of testosterone in men and big amounts of estrogen's in women.

Sexual maturationSexual maturation In the sexual maturation the most important changes

are the menarche and the spermarche. Menarche: Is the first menstruation in females. Spermarche: Is the first ejaculation in males.

After that, there is a period of sterility that can least about one year in which menstruation and ejaculations occur but no eggs or sperm are released (Tanner, 1990).

The pituitary gland releases hormonal signals that begin physical transformation, because of different causes like genetic factors.

But they are not the only cause, for example: In young women physical exercise can delay the onset

of the physical changes, associated with puberty (Brooks Gun, 1998).

Family conflict and the absence of fathers predicted an earlier onset of menarche (Moffit, 1992).

An increased psychological distance between girls and their fathers predicted an earlier menarche.

When fathers had good quality relationships with their daughters the onset of pubertal maturation came later.

These studies highlight the importance of environmental factors in sexual maturation.

Early maturation carries advantages for boys (Jones and Bayley, 19500):◦ Late-maturing boys are characterized as lower in

physical attractiveness, masculinity, and were rated as more childish.

◦ Early-maturing boys are characterized as independent , self-confident, and as being better leaders and athletes, and they use to have a much more positive body image, because with the puberty they gain height and muscularity.

However, in girls early maturation has the contrary effects:◦ Early-maturing girls are less popular, less self-

confident, held fewer leadership positions and tend to have a poorer self body image, in part because in the pubertal maturation there is a gain of weight.

Behavioural problems have been associated with early maturation.

Caspi and Moffit (1991) said that when stressful events such as early maturation occur, girls may highlight dispositional factors.

Brooks-Gunn and Warren (1995) believe that psychosocial factors (parental warmth, parental approval, and the level of family conflict) play an important role in how girls react to early maturation.

There has been also found that early-maturing girls tend to have smaller networks of friends and to associate with older friends who often engage them in risky behaviours like smoking, drinking or sexual intercourse.

Contextual and psychosocial factors play an important role in behavior, but not all early-maturing girls will experience problems.