Notes on Heredity and Family Resemblances in Intelligence

For a common person, resemblances among the family members in terms of intelligence are an indicator of the influence of heredity on different abilities of the some family. Psychologists have carried out some systematic studies to see the influence of heredity on behaviour pattern of the members of the family.

However, in a family, it becomes difficult to differentiate between the hereditary and environmental influences. If, in a sample of large family groups one notices inter-group similarities, it may be attributed to their heredity while the rest of the influences might have been caused by the environment. These researchers have tried to test the following hypotheses:

1. Correlation to be higher:

If environment is an important factor, correlation between like-sexed siblings should be higher than those between different-sexed siblings. The environment is more closely similar to the two brothers or two sisters than it is for a boy or a girl-in the family.

2. Correlation Co-efficient to be Lower Environment:

If environment is an important factor in the production of intellectual traits, correlation coefficients between siblings should be lower for these traits than for physical characteristics like eye colour, height and head measurement, which are thought to be almost entirely hereditary.

3. Correlation Mother and Children:

If environment is an important factor, correlations between mothers and children should be higher than those between father and children. The mother is more closely associated with the children during their early formative years.

4. Correlation between Siblings:

If environment is an important factor, correlations between siblings should be higher than correlations between parents and children. The fact that they belong to the same generation would operate to make the siblings’ environment more similar. Scattered evidences have been cited both for and against each of the hypotheses presented above.

Way for Evaluation

The best way to evaluate the influence of heredity is to take subjects who experienced the same environment but who are known to differ in genetic endowment and compare them with a group in which both heredity and environment are the same.

We can do it by comparing the amount of differences between identical twin pairs with the amount of difference between fraternal twins or between siblings. Two terms viz., concordance and discordance are used in such studies.

These can be explained as under:

1. Concordant:

If both the twins show certain characteristics, they are called to be concordant.

2. Discordant:

If one twin shows it and the other does not, they are called discordant.

Whenever the percentage of concordant pairs is much higher in case of identified twins than fraternal twins, there is a sound basis for concluding that the traits in question have a genetic origin. Role of Heredity

The role heredity plays in certain kinds of psychiatric difficulties has been established by a large-scale study of New York Psychiatric Institute under the leadership of Kalama (1950). The study was started with a group of persons with certain diagnosis and then to locate and check up on their blood relatives.

In case of individuals who suffered with schizophrenia (psychosomatic disease), it was found if one of a pair of identical twins has the disease, the chances are that eighty-six times out of a hundred the other twin has it also. The other fourteen who are not frankly schizophrenic have schizoid personalities.

Some Other Research Works

Significant research work has also been done to study neuro anatomical traits in the house mouse and the determination of associated differences in behaviour. Stores (1967) found highly significant and substantial strain differences.

Studies on brain weight have given an ample basis for optimism regarding our future ability to manipulate, at least, some of the compound traits which underline it.

Roderick et al (1973), and R. Wimer et al. (1969) show that identifiable genetic control exists for the sizes of some specific portions of the central nervous system.

Studies conducted by Terries (1964), C. Wimer and Prater (1966) and Wimer et al. (1969) provided some evidence to support a positive between brain weight and activity in the open field.