These children have mental deficiencies.Stones (1978:301)says," educational subnormality has been applied to those children whose attainments are lower than 80% of the attainments of average children of the same age." This children can do some mental exercises.Usually ESN is for the children in special schools or classes.In these specialised areas these children get individual attention from skilled and specialist teachers ,which results in these children benefit immensely.The major causes of this retardation is because of natural circumstances which are poor genetic potential and organic disorders.
Genetic Potential:The poor genetic potential is the mental disorders passed on from parent to child.
At fertilisation of the egg in the uterus the genetic characteristics passed from parents to the off-spring of individual parents are transferred into the embryo through genes.The genes transfer many human characteristics which are the biological blueprints of physical and mental features found in the parents. These characteristics are passed from generation to generation. A child can inherit mental disorders from parents and these account for mental retardation.Some cases are because of chromosomal defects(A chromosome is a thread in every animal or plant cell carrying genes).
Many of the defects result from ancient causes ,thus abnormal genes are passed on through ancestors who carry them,but may themselves not affected.
When two such people who carry some abnomal genes mate ,25% of their offsprings are likely to be defective mentally or physically. This happens frequently when two close relatives conceive ,for example first cousins ,children of brothers or sisters. As result of this may be amaurotic idiocy(amaurosis =blindness) The child develops blindness ,paralysis and idiocy (extreme stupidity) after birth,but is normal at birth. More oftenly the child may remain normal for two years ,after which the consequences may be fatal by the time /she turn five years old. The disease is common in communities which culturally promote marriage within their family lineage.Amaurotic idiocy is found among different races around the world .In most cases the effects of these abnormal are felt when the child is changing from childhood to adulthood. In this circumstances the development of idiocy is less rapid.Some recessive (weak characteristic passed on by means of genes to later generations )genes may cause microcephaly ,thus the brain is very small(half the normal weight at times),but the general health of the child may look good.Certain types of spastic (physical disbled because of faulty links between the brain and the motor nerves)paralysis which affect the legs and arms are a result of heredity.Heredity can cause defects like imperfect development of eyes (microphathalmia)associated with mental defects.
If there has been a recent changes of gene in the parent ,severe defects of a single child in a large normal family may occur.This commonly happens when someone suffers from a disease in which there is tumor (disease growth in some part of the body like in the brain)formation which is accompanied by epilepsy and mental defects.Children whose deformities caused by recent changes of genes have deformed craniums ,clumped fingers and toes,patchy pigmentation in their skins can be caused by enlarged nerve endings .All these children suffer from mental defects.
Influence of Chromosomes:Chromosomal defects cause mongolism.Child(1978:200)uses the example of Kallik family to explain the influence of heredity on retardation:
"A certain Martin Kallikak had children by two women ,one was feeble-minded,the other was of normal intelligence .The feeble-minded mother gave rise to higher proportion of feeble minded descendants whilst the mother
with normal intelligence had no feeble-minded children at all."This therefore concludes that heredity plays a major role in causing retardation .However its role is not certain like environmental factors and their influences felt at the same time.Either heredity or environment factors cause this handicap.
Influence of Radiation:Irradiation shown in animals which exposed to radio&active material by doses of X-rays and numerous drugs such as selenium applied to developing embroys have produced in-born deformities ,examples are cleft palate and bad development of the kidneys.
If a pregnant woman therefore exposed to irradiation in early pregnancy may damage the foetus. The Nagasaki and Hiroshima atomic bombs destruction is the good example.Major deformities are believed to be exposure of mother to radio-active rays
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