Gregor Mendel (1866) discovered the law of inheritance in hybrid peas growing in the garden of an Austrain monastery. His law was found applicable to animals also. His law can be summarized as under. “If a man who is homozygous for blue eyes marries a woman who is homozygous for brown eyes, the children of the couple will have brown eyes only (Homozygous condition is that condition in which information concerning a given characteristic differ in the paired gene position). If a homozygous man marries to a heterozygous woman the distribution of children from the couple will be such that one fourth of them will be homozygous for brown eyes, one half of them, will he heterozygous and one fourth of them will be homozygous for blue eyes. By this law, Mendel concluded that all genetic informations come to the individual in units rather than in graduated series. In other words, we receive from our ancestors genes controlling the development of specific unitary characteristics not a composite of traits called tendencies. The second conclusion that can be drawn from this law is that characteristics of men do not remain constant. They tend to vary continuously along a dimension of genes. 

 Studies on Influence of Heredity

How great the role of inheritance is in shaping the personality of an individual by the process of growth and development can be understood by the following studies:

1. Galton : He was the first psychologist who conducted studies on the nature and extent of genetic influences in man. He studied 997 eminent British people and found that there were 322 people out of 997 who were also distinguished. He also studied 997 average people and found that only one of them was eminent. He thus concluded that eminent men were found in families which have already one eminent member at least. He also found that decreased instances of imminence were seen when eminent people decreased their relationship with eminent persons. Thus, according to him eminence is inherited from generation to generation. He also studied some people of U.S.A. who were given better educational facilities and compared them with the eminent people of U.K. who were given average educational facilities. He found that people of USA were not better performed than that of UK.

2. Goddard (1914): He studied a Kalikak family of USA. Martia Kalikak who was a soldier in the American revolution, developed illegal sexual relation with a feeble-minded lady and an illegitimate child was born. 480 descendents were traced from the fainily tree of this illegitimate boy. Out of them 143 were feeble-minded, 291 were borderline normal and only 46 were found normal in intelligence. After the revolution when Mr. Kalikak married a normal lady a legitimate child was born. 496 descendents were traced from the family tree of this boy. All of them except two were found normal or above normal in intelligence and they became teachers, lawyers businessmen etc. This study prov intelligence is inherited from one generation to the next. These two studies show that heredity plays an important role in determining the traits. But the conclusions derived from these two studies can not be fully relied upon because of the following reasons.

(i) They do not distinguish between biological and social inheritance. Their studies combine these two factors. So, it is very difficult to isolate the contribution of gene in shaping the personality.

(ii) Testing material used in these studies was not perfect and the survey is also unsystematic and unreliable.

(iii) The researchers were already biased in favour of hereditary factors. So, their conclusions can not be relied upon.

3. Kellogg and Kellogg : In order to study the relative influence of heredity and environment they conducted a systematic research by taking their own son and a chimpanzee. Their respective ages were 10 months and 7.5 months. Both of them were brought up in the same environment with similar type of facilities given to them. Their behaviours were systematically studied at regular intervals. It was found that in the beginning the chimpanzee surpassed the son in motor skills of jumping, running, climbing, etc. Chimpanzee also learned some social skills such as eating with spoon and drinking from a glass, but he could learn 93 words only. But later on, the son caught him up in all areas of development except physical strength. This study shows that heredity sets a limit for maximum development which can not be improved even by providing the best environment.