.. tive if they are begun early in the life of the child. The reason behind that is that the programs are better able to create lifelong changes in capacity to generate and sustain responses to cognitive stimulation. These programs entail the development of visual and auditory competence as well as encourage attention and labeling which help cognitive development in children. Storfer notes the Drash and Stolberg experiment were it was found that extraordinary high competence, emotional maturity and speech development were attained by children as a result of an enrichment program designed to modify the behavior of parents during the first year of their childs life.
The Stanford Binet scores of the four children averaged one hundred fifty-five. Before we start to discuss Hereditary influences we must initially note that both genetic or hereditary and environmental influences are equally important, according to Dobzhansky. Many psychologist refer to genetics as one of the major influences upon the level of individual intelligence. Cancro states that the expression of like produces like is an oversimplification with a strong basis underlying it. He points out that offspring are more likely to be similar instead of unlike to their parents on any genetically loaded trait. Cancro expresses that genetic as far as heredity is concerned, is a distinct property of a population.
This statement was made to note that inheritance is not a measure of an individual or of the trait itself. Inheritance estimates the proportion of the total variance in a proportion of the total variance in a population at a particular point. Inheritance for intelligence usually falls between .70 to .90, according to Cancro. This number depends on the population which is being considered and on the specific test or method being used. The Polygenic model suggests that both environmental and hereditarian variables are required to explain differences in individual intelligence.
The Polygenic model is basically the same as the deprivation model from environmental influences. The difference between these two model is the fact that the Polygenic model introduces three new variables. The first of these variables is the mid-parent and childs heredities which refer to the genotypes of intelligence and furthermore result in quantitive variations in cognitive functioning. The second variable of the Polygenic model is referred to as mid-parents and childs intelligence. The last variable of the model is the childs heredity which stands for all the sources of variance in the childs heredity accounted for by the mid-parents heredity.
A connection between each variable supports the model. The path is the connection and the path taken from parental intelligence to social status is the most important. according to Eckland, it is the primary link between genetic and environmental parts and it also forms the weakest link in the genetic loop. Two other links in the models loop deal with the proportion of variance in intelligence and how this is due to genetics. These other links are labeled as PMP and PIH. Since the coefficient or magnitude of this proportion is increasing then the coefficient is a population statistics and always depends upon the absolute value of variance of trait factors in the environment. The paths of the two links change with any strong change in the environmental factors.
This means that if either one of the paths from parental social status and parents intelligence to the childs environment increase then we would see a decrease in the proportion of the variance in measured intelligence. The last link to consider in the genetic loop of the polygenic model is labeled PHP, and is highly strong. Cancro points out that a child receives half of his or her genes from each parent. This makes the correlation between parent-child intelligence equal to .50. Cancro warns that this correlation is considerably larger since this figure is only subject under conditions of random mating.
This means that the closer the parents resemble one another then the more closely children will resemble their parents (73). This holds true to the fact that males and females of like intelligence would generally end up in similar settings such as school dropouts or graduate students. These factors either limit mating or pair like individuals together and therefore changing the previous correlation. If both parents have above average intelligence then their children will most likely exhibit this trait. This evidence, according to Canro, therefore is partly due to the hereditary basis of intelligence.
According to kinship correlations, proportions of genes of intelligence that are held in common by two relatives enable us to predict correlations between their IQs. Identical twins, for example, posses identical genes. Vernon points out that the interclass correlation of identical twins should be 1.0 since they share the same genetic makeup. Heritability analysis covers the subject of twins among other kinship relations. The correlations, according to Vernon of genetic expectation for both dizygotic twins and non twin siblings raised apart or together is .50. According to studies performed on these groups, there is a high similarity between the genetically expected and the obtained results. Vernon states that the results of his tests support the conclusion that both genetic and environmental components have a significant effect upon the intelligence of the child.
There has also been some research done on identical twins who live in different environments. They have been compared with siblings who are not twins but live in the same environment. The correlation results for twins who live apart is .75 and .24 for no-twin siblings who do live together. It seems that together, these two correlations almost add up to 1.00 which is the total phenotypic variance. Vernon points out that the effect of genes is much more powerful than that of the environment. Even though the precise values of the correlations are of dispute, analyses of kinship data, concludes Vernon, provides the most convincing demonstration of genetic influence on intelligence.
Undoubtedly ,the subject of intelligence can be defined in many ways. To better understand intelligence psychologist have rendered two main influences as cause for variable intelligence levels. These two main influences as discussed previously cannot be explained as one being the main determinant of intelligence. This two influences are environmental and hereditary influences. Psychology Essays.