Behavior geneticists assess the question of inheriting personality. Are our genes responsible for our creativity, aggressiveness or confidence? Examining personality traits through a genetic focus is an obscure task. Methods employed by behavior geneticists involve epidemiological studies, such as screening family pedigrees, conducting twin heritability studies, and adoption studies. Personality is best described as what makes up a person, their traits and individual differences that make them unique.
There has been much research undertaken as to what actually causes a personality to develop whether it is nature (genetically inherited) or by nurture (the environment) research has shown that it is a combination of both. (Walter, shoda, smith 2003) Human society is complex and this presents researchers with difficulties in measurement of the environmental effect and to define exactly what causes personality. Psychologists and behavior geneticists have tried to estimate contributions made by genetics and the environment to individual differences through heritability.
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Heritability is when research has been carried out to establish the contributions of genetics and the environment to a population sample. This is based on knowing the birth relationship (genetic relatedness), measuring the trait in question and making comparisons between groups with differing levels of genetic relatedness. The amount of variability in a trait or physical measurement within a population is accounted for to show how much has been inherited (genetically) and the percentage remaining is the environmental contribution. Twins were an excellent source of study since their DNA is identical.
Before 1970 there was not much recorded information about twins, however there are now larger information sources and larger samples have become available. In Sweden and Finland the central recording of twins raised together and apart also improvements in the interpretation of statistics and technology enabled larger samples to be examined. Findings from heritability studies have shown that personality traits are associated with genetic influence, however this can vary depending on the trait measured, eg neuroticism shows heritability as 30% but measurements of extraversion/introversion show heritability as 50%.
Measurements could be inaccurate as variables have to be considered eg environmental factors – twins that have been reared apart may have still lived with a family member and could still be brought up in a similar way. The media stories have focused on successful reunions of twins previously separated, twins separated may spend years getting to know each other before they are researched which would be enough time to adapt their personalities.
The time separation aspect could mean different things, eg some twins researched had actually spent some years together. (walter, shoda, smith 2003) Twin studies have often used different measures of a person, therefore the results may be unreliable unless the same measurement is taken each time. Other research in families involved examining differences in relatedness between other family members ie siblings, half-siblings, cousins, parents and children. There have also been adoption studies.
Research has shown that nature has a proportion of about a third effect on personality, which would infer the larger effect on a personality derives from the environment. There is continual interaction between an organism and its environment from conception throughout life, environments that are both physical and made up with other people. Individual differences psychologists describe environments as ‘dimensions’ ie whether the child has been raised in a controlled or a relaxed environment, the mother’s health and well being and the parents relationship.
Personalities can change dependant upon the situation that the person is in. The Stanford Prison Experiment is an example of a social experiment where volunteers undertook new roles. Twenty four were selected after various tests to rule out medical, psychological and other tendencies. They were told that the research was to study the psychological effects on prison life, the experiment took place in a mock prison environment within the university.
The experiment was cut short because prisoners became demoralized and showed signs of stress, depression and others lost touch with reality. Guards behaved in authoritarian and aggressive way, some became sadistic. The research here showed that social situations have powerful effects on behavior. Researchers have used various forms of evidence that seem to indicate that personality is developed through an interaction between genetics and the environment therefore it would be wise to conclude that only a portion of a person’s personality is inherited.
Differing situations should be accounted for when comparing the results, to date it has been difficult to define what the exact ratio of heritability – environment is, research has shown heritability to be approximately 30%.
Introduction to Personality: Toward An Integration, Seventh Edition by Walter Mischel, Yuichi Shoda, and Ronald E. Smith. John Wiley & Sons; 7th edition 10 Jul 2003