1. Endocrine Glands
Ductless glands send their secretions directly to the blood without ducts. Their secretions are called hormones. These hormones are responsible for many changes in the personality. Different glands secrete one or more type of hormones. A description of the effect of some of the ductless glands will show the extent to which personality is influenced by them.
Pancreas sends insulin to the blood. The amount of sugar in the blood depends upon the amount of insulin in it. When the deficiency of insulin, i.e., sugar, is in the body the mental powers are weakened and the personality of the individual seems less balanced. His book is changed; temperament becomes irritated and fear increases.
(ii) Thyroid Gland
Thyroid glands have a very important function in the development of physical structures as well as mental development. If it is absent since the very birth the intellect of the child does not improve.
(iii) Adrenal Gland
Adrenal gland secrets adrenaline has an important influence upon personality. Its excess creates the sexual traits in men or women. Its excess in women is responsible for the absence of the rounded contours and feminine voice. It organizes the organic capacities in the time of emergency.
The secretion of the gonads i.e., sex glands is an important influencing personality. Gonads secrete sex hormones. Sex hormones are very helpful in the increase of sex interest. In adolescence there is a special increment in sex hormones.
Hence, changes are observed in the individuals according to their sex in man one finds the manifestation of manual characteristics such as beard, moustaches, high pitch in voice etc.
While in the female there is development of mammary glands and other womanly traits. The processes concerning pregnancy e.g., menses, pregnancy, the bearing of the child and maternal behaviour is very much influenced by the sex hormones.
(v) Pituitary Gland
The hormones secreted by the pituitary glands control other glands. The hormones secreted by the front part of the pituitary glands increase the activity of other glands as well. The hormones created by the back part of the pituitary glands control the blood pressure and the metabolism of physical growth.
In the time of physical growth the bones and muscles of the individual grow speedily due to the activity of these glands in its excess, the height can go even up to 7 to 9 feet.
But because after excessive activity this gland becomes very much inactive, these very tall persons die at an early age. If the activity of the pituitary gland is very much deficient in the time of development, individual remains is midget, rough his intellect is normal and the physical structure is not unattractive. It the activity of this gland is normal during the developmental period and becomes excessive afterwards the hands, feet, nose and lower jaw, etc., becomes broad.
The effect of the hormones is influenced by the heredity as well as the environmental factors. But still the excess or deficiency in their activity created some changes quite apparent in the personally of the individual. It is not necessary that the excess of the excess of the secretion of any one of the particular glands should always show some special influence in the body e.g., the excess?
If sex tendency should not always be supposed as due to the excess of the secretion of the sex gland, since different glands also interact upon each other due to which the activity of some is increased while that of others is decreased. The sex behaviour, for example, is very much influenced by social norms circumstances, habits and many other things.
Other important biological factors affecting personality is physical structure. It is seen in daily life that often the fat men are easy going and social, while the thin persons are self- controlled, irritated and un-social.
While the thin persons are self- controlled, irritated and un-social. Thus, the physical structure has some relation with the temperament. But even the instances contrary to this rule also exist.
As a matter of fact, the relation of physical structure and the temperament has not been definitely established. More experiments are required in this direction.
The experiments conducted so far have been mostly on college student. Before one arrives at some definite conclusion, experiments must be conducted on adult persons as well. But even after that, the problem of the basis of co-relation remains un-answered, simply by co-relation the temperament cannot be taken as a result of physical structure.
It should also be remembered in this context that the physical structure makes a difference in other behaviour towards a particular person. It is observed that our behaviour towards different individuals is modified, to some extent-according to their physical structure.
3. Body Chemistry
Another important biological factor affecting personality is body chemistry. In ancient times the difference of temperament was supposed due to differences of chemical elements in different men. Thus, the nervous personality was taken as the resultof excess of nervous fluid.
It was supposed that the sanguine persons have an excess of blood, the choleric persons and excess of bile, phlegmatic persons and excess of phlegm and the melancholic persons, an excess of spleen. This principle is not accepted in modern psychology, but still no psychologist denies the relation of personality with the proportion of chemical elements in the body.
These chemical elements are two types. Some reach the body from outside while some are created in the body itself. Thus, the drugs have sufficient effect on personality; the behaviour of the drunkard is an example of such effect. Different types of intoxicating drugs have a clear influence upon the personality of the individual.
The deficiency of different vitamins also causes some change in the personality. With the increase or decrease of the quantity of sugar in the body, the physical and mental state of the man is very much changed.
Besides the above-mentioned biological factors many other factors influence personally, e.g., sex, intelligence, intellect and nervous system, etc. The difference in the sex of male and female create an essential difference in their personality, though it has been established that much of this difference is caused by social and cultural environment. Galton and Goddard believe that intellect is absolutely hereditary.
The modern psychologists do not agree with this hereditary view through the influence of heredity is not denied. The environment affects intellect, but the development of intellect is ultimately limited.
The influence of special talents, as that of music, mathematics, etc., on human personality is very well-known. Like the intellect, the talents are also generally hereditary.