Exactly how much is personality development affected by genetic makeup and the environment? In studies comparing behavioral traits in identical and fraternal twins, researchers found that genetic differences can account for 40 to 50 percent of differences in personality traits, while environmental influences account for about 30 percent of differences in personality traits.
So, why should we study about what role biological and environmental factors take in the development of personality? What does this have to do with us? The answer is this - how we look at the nature-nurture issue affects the way we look at people, especially children, look at why they behave in certain ways, and how to deal with it. So why not start looking into each of the factors now?

Genetic factors
Biological factors such as our hormones and brain structure influence our behaviour, but our genes do not have programs for specifying our personality traits. Their actual job is to control the development of our nervous and endocrine systems, which in turn controls our behaviour. Therefore, our genes do not have direct control over our personality traits, but they do have a role in influencing our behaviour. Complex human behaviour are not determined by single genes.

In human chromosomes, there are six billion base pairs of DNA. But the most amazing thing is this - of that six billion, only six million of them are different between individuals! That means 99.9% of the base pairs of DNA are shared and identical in each and every person. Nonetheless, each of us still have enough genetic differences to make us different from others. Even siblings, born of the same mother and father - which means conceived from the same source of mother and father, have two million base pairs of DNA.
Numerous stories of identical twins, separated for a long time since childhood, suggest that personality is largely inherited. Here is an example.
Jameel and Khaleel are a pair of identical twins, separated four weeks after their birth.They grew up separately. They reunited after 40 years. They discovered that they both have same choice for car , cigarette and many more similar habits .
Another pair of identical twin males were separated at birth, adopted by different parents and raised in different countries. These two men were both found to be extremely neat. Not only in tangible aspects - their lives were neat. Their clothes were always clean and smart. They were always strictly on time. They washed their hands so often that they were raw and red. Both twins were asked why they were obsessed about neatness. The first twin answered,
"It was because of my mother. When I was growing up, she always kept the house perfectly ordered. She insisted on every little thing returned to its proper place, the clocks - we had dozens of clocks - each set to the same noonday chime. She insisted on this, you see. I learned from her. What else could I do?"

The other twin answered in quite a different way. He said,
"The reason is quite simple. I'm reacting to my mother, who was an absolute slob."
As you can see quite obviously, the twins' obsession with neatness is not caused by their mothers. The performance of their mothers had little to do with their need for cleanliness. It is more likely that it is caused by genetic factors.
When people think of the gene's role in the formation of a person, they usually put more emphasis on physical appearance. On the other hand, we tend to see personalities of individuals as the result of experience - people lead different lives, have different sufferings, experience different things, and therefore each person has a different personality. However, today we can understand more and more about how genes have a force too. Research in behavioral genetics has supported the idea that personality is partly inherited. Psychologists have summarized the results of twin studies that focused on the Big Five personality traits. Results have shown that identical twins resemble each other in personality than fraternal twins. This suggests that personality is partly inherited.
Infants, just a few weeks old, display differences between each other on how active they are, how responsive they are to change, and how irritable they are. Some babies cry constantly. Others seem to be happy and stay fairly quiet. Each infant has different mood-related personality characteristics, which are called temperaments. Because differences in temperaments in infants can be observed in such an early stage, the traditional view that an infant's behavior is formed by the environment the infant is in, during its early stages, is questionable. Research has shown that infants are born with temperamental differences.
As seen from the above, genetic factors play a major part in the formation of personality, but not every personality characteristic is originated from genetic makeup. We will look at how genetic factors affect environmental factors and their correlation in personality development later in this section.

Environmental factors
Carl Rogers, a famous psychologist, put a lot of emphasis on how childhood experiences affect one's personality. The degree of effect of what happens to a child when he/she is at a developing stage on his/her personality development depends on when it happens. Many psychologists believe that there are certain critical periods in personality development, which are periods when the child will be more sensitive to certain environmental happenings.

Most experts believe that child's experiences in the family are important for his/her personality development. These include whether a child's basic needs are well met and how a child is brought up, which could leave an enduring mark on the child's personality. For example, children who are toilet trained too early or have their toilet training carried out too strictly may become rebellious.Children can learn appropriate behaviour  especially when there is a good relationship with parents, children are also affected by siblings.
How about culture and society then? Does the culture and the society we are brought up in affect our personality?
An American anthropologist Margaret Mead has shown how social and cultural factors has an important influence in personality development. Members of two New Guinea tribes are of the same racial store and live in the same area. However, one group is peaceful, friendly and cooperative and the other is group is, on the contrary, assertive, hostile and competitive.
Researchers, when comparing cultural groups in specific aspects of personality, have found some interesting differences. Northern European countries and the USA have individualistic cultures that put more emphasis on individual needs and accomplishments. Asian, African, Central American, and South American countries have collectivist cultures that focus on belonging to a larger group, such as a family, tribe, or nation. In these cultures, people believe cooperation is more important than competition. Individualistic cultures and collectivist cultures are very different.

Two examples of these differences would be "locus of control" and "self-monitoring". Studies have shown that in general, Western cultures gave a more internal locus of control as compared to Asian cultures. It has also shown that people from industrialized places are generally more internal than people from developing places. Cross-cultural studies of self-monitoring has shown that those from the US and Australia score higher in self-monitoring than people from Taiwan, Japan, Hong Kong and Korea. Professionals have also done some comparison on the American and Asian ideas of self. Their studies indicate that American parents teach their children to be independent, to feel good about themselves and to see themselves as special individuals. Children are encouraged to do well in competitive activities and to become outstanding. American children learn to value themselves by their credits, abilities, accomplishments and by what they own. Those carrying out this study conclude that the American culture encourages an "independent view of the self". American youngsters tend to exaggerate how unique they are and overestimate their skills and capabilities.
Asian cultures, on the other hand, encourage an "interdependent view of the self". This view focuses more on the basic bonds between people, and how each connection relates to each person. Parents may teach their children that they can rely on family and friends. Asian children are taught to be modest about personal achievements, and to see themselves as a fraction of a larger whole. Children are taught to try to fit in with others and not to stand out from the group. The researchers thus conclude that typical Asian children learn to place value of themselves in terms of the group they belong to - their relations with others and group achievements. And because of this, they do not need to exaggerate how unique or capable they are. Asians tend to see themselves as similar to their friends than Americans and they put less emphasis on personal achievements than Americans may.

As seen from the above, the environment we grow up in, including the home environment with the influence of parents and siblings, and the culture and society plays an important role in personality development too. Now we will look at the interaction and correlation of genetic and environmental factors.

interaction of Nature and Nurture
Most psychologists today agree that not only does both heredity and the environment play a role in the development of personality, but also that these two interact to influence the development of personality.
A person's temperament is formed both by genes and environment. Researchers state that the continuity and discontinuity of temperament is resulted from the interaction between the inherited characteristics of the individual and the environment. They especially believe that in order to have a healthy development, there must be a goodness of fit between the individual's temperament and the home environment. When parents of a difficult child give him/her a happy, comfortable and stable home life, the child's negative behaviors will improve as he/she grows older.
Most behavioral traits are multifactorial, which means they depend on more than one genetic or environmental factor. Even from the moment of birth, biological factors and environmental factors are interacting to form a person's personality. Parents not only pass on their genes to their offspring, but also provides them with a home environment to live in, both of which are results of the parents' genes. There is a correlation between the child's inherited characteristics, which is called genotype, and the environment. Here is an example to illustrate. Intelligent parents will have a higher chance of giving birth to intelligent children. At the same time, intelligent parents will be more likely to provide their children with a good learning environment, one which is intellectually stimulating, by teaching their children themselves and giving them books, lessons, activities and so on.

Environmental influences outside the family environment, such as school and friends, are often more important to the development of personality. However, these apparent "outside influences" may have more to do with genes than it would seem at first. People seek out or even create environments to which they are genetically predisposed. For example, a combative person is more likely than a peace-loving person to find an environment in which arguments are likely to take place, or to create such an environment by starting fights.
As seen from the above, an individual's genotype and the environment are not just independent sources of influence that add together to form an individual's personality. The genotype is in correlation  with the environment. An individual's genotype also shapes the environment. Interaction and influence of heredity and environment with each other form a person's personality.

Behaviour consistency

By now you should know that personality is the fairly fixed patterns of our thoughts, emotions and behavior under different circumstances. Our personality makes us act in certain ways-- it gives us a consistent tendency to behave in a certain manner. Therefore, consistency is a core concept of personality. But how stable is our behavior? Different psychologists have different opinions. There has been a lot of research on stability of behavior over time and across situations, which is behavioral consistency.
There has been research on the study of stability of children's behavior, however, there has been different interpretations on the results because some behaviors and some phases in development are more stable than the others. An example of a reasonably stable behavior pattern is aggression. Children who appear to be aggressive may grow up to be aggressive adults. Generally, children's behavior become more stable as they become older.

To make matters even more complicated, some characteristics may be shown in different ways at different ages. "Well, what does this mean?" you may ask. Here are two examples:
A child is aggressive. In kindergarten, the child may hit others. As he/she becomes older, the physical attacks may turn into verbal ones, like insults and criticism.
Next comes the matter of consistency across situations. Do people behave in certain ways only under particular situations? Or is it true that people have traits that show up in a wide range of settings? So the main question is--which controls behavior: the person's traits or the situation? The answer is that BOTH of them do. They work together to make a certain person behave in a certain way under a certain situation. Some people may side more with the situational factors, believing that individuals will show little consistency except when the environment remains consistent. Others who stress on the domination of personality will expect individuals to display consistency and stability.
Therefore, a consistency paradox appears. By stressing the influence of situational factors on behavior, the common assumption of cross-situational consistency in behavior is challenged. Recent research in social psychology supports how behavior may change under different circumstances

Personality and profession