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Comparison between environmentally and genetically influ~6c3

Comparison Between Environmentally and Genetically Influenced Traits

Intelligence is the level of competence, ability to learn or to some people

it is how well an individual performs on an IQ test. The structure of

intelligence is best subdivided into two significant categories. They are

environmental and hereditary influences.

Environmental differences can be divided into different factors. The

deprivation model of social class and intelligence consists of three

variables. These variables explain, in terms of environmental factors,

development and performance which are correlated with social status.

The first of these variables consists of the combination of birth order,

nutrition, and prenatal care. Children who are first born, on average

score better on mental tests. There is a definite higher number of first

born children among higher socioeconomic groups as opposed to lower

socioeconomic groups. According to Bruce Eckland, children of higher

economic class tend to be brighter, on average, than children of lower

economic groups (65). Both prenatal stress and malnutrition, impair

development and are found much more frequently among lower

socioeconomic classes. According to Philip E. Vernon, the fetus can

have lack blood supply and growth of the fetus can be disturbed if the

mother takes certain drugs or suffers from certain diseases. Severe stress

on the mother can also be hazardous to the fetus (84). These conditions

expressed are both genetic and or resulting from environmental conditions

and are known to as constitutional factors. The second variable of the

deprivation model which helps exhibit differences in performance is the

cultural variable. It seems that lower socioeconomic classes experience a

unique pattern of behavioral and psychological traits which impair

development in children raised in these conditions. The last environmental

variable that accounts for differences in the cognitive development is the

social cultural variable. This variable includes deprivation which involves

socially structured inequalities in education and other social opportunities

for improving performance. Sidney W. Bijou states that in order to help

development, an ample supply of physical stimuli for cognitive

development is favorable along with the people who have to manage

these stimuli in contingent relationships after the birth of the child (230).

Another environmental contribution to intelligence, which Bijou points out

is the availability of people who enhance opportunities for cognitive

development. These people have the job of shaping responses and for

bringing responses under stimulus control. Examples of this contribution

are conceptualizations and symbolizations. An unwanted contribution

would be some situation where there are people with marital discord or if

they are economically poor. Another contribution, explained by Bijou,

refers to the kinds of reinforcers in effect in cognitive situations. An

example of this contribution would be to use positive reinforcing

contingencies. A hampering situation would entail adults who use

aversive, neutral or random stimulus contingencies. The last of these

contributions refers to the schedules of reinforcement. These

contributions are categorized by a high number of people who schedule

contingencies of reinforcement in ways which maintain the cognitive

repertories acquired (230). Greenfield insists that people learn what they

need to accomplish a goal presented by the environment. The

specification of a particular set of goals by the environment not only

determines whether learning (255). In an experiment done on children,

Werner and Kaplan found out that variable verbal and action contexts

for a certain concept provide a way of generalizing that particular concept

by differentiating it from its context. Educationally this provides a wide

variety of action goals but even more important during the initial stage

instead of the later stages. This goal structure of the environment plays a

most important role in early life and then gradually declines in importance,

according to Patricia M. Green field. Greenfield also points out in a study

administered by Garves that middle class mothers give significantly more

positive feed back as opposed to lower class mothers who give a high

rate of negative feedback to their children. This scenario leads to feelings

of failure on the on the child’s part. In other words, lower class mothers

believe that their goals cannot be attained, therefore giving way to a

feeling of discouragement and a response of negative feedback to their

children. This condition produces a lack of self-determination for the

lower class mothers which then in turn gives the child himself lack of

self-determination among other things. The home environment is also a

major factor for cognitive development. For starters, middle class

mothers may mothers may supply their children with an image of goals

towards which school is aimed. On the other hand lower class lower

class families seem to lack this positive feedback all together (252-260).

Vernon states that child and parent interactions greatly influence the

cognitive growth of the child. Evidence of the previous is best

demonstrated in the work of Wulbert et al. Wulbert’s experiments

compared the homes and mothers of twenty children who were retarded

in language and matched them with twenty normal children. The mothers

of the language retarded children had lower results in emotional and

verbal responsiveness and were more liable to punish their children than

the mothers of the other twenty normal children. Davis helps to illustrate

the views of Vernon. Davis described a girl who lived with a deaf mute

mother and did not develop any speech until she was moved from that

environment (p.131). Spitz, on the other hand, describes the effects of

early hospital upbringing but still helps support Vernon’s views. He

studied infants who layed inside of their cribs with very little to look at

unless they were being fed or cleaned. Many of these infants died and all

of them, including those that died fell into a state of "apathy" (132). Both

of these studies support Vernon’s views to the point that parent and child

interactions influence the child’s cognitive development and growth ,

especially early in life. It seems that environmental differences play a

major role on the level of intelligence of an individual. Evidence of

environmental differences and its impact on intelligence is better illustrated

through higher IQ gains generated by the help of environmental

enrichment programs. These programs are more effective 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 child’s 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 child’s 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-parent’s and child’s intelligence. The last variable of

the model is the child’s heredity which stands for all the sources of

variance in the child’s heredity accounted for by the mid-parent’s

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 model’s 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 parent’s

intelligence to the child’s 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.

Word Count: 2035



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