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 egg and sperm, 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.
Jim Lewis and Jim Springer are a pair of identical twins, separated four weeks after their birth in 1940. They grew up 45 miles apart in Ohio. It was not until 1979 that they reunited. They discovered that they both drove the same model blue Chevrolet, chain-smoked Salems, chewed their fingernails and owned dogs named Toy.
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?"
Produced for Thinkquest Internet Challenge 2000.
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