It is certainly true that everyone seems to have a personality, but why is that so? This paper will seek to examine some of the available evidence in order to answer this particular question.
One possible explanation is that personality has a gene linked on a chromosome. For instance, on chromosome 11 there lies a gene called the D4DR gene. It provides the genetic programming for the development of a protein called "dopamine." This protein is a neuro-transmitter that is released from a pre-synaptic axon terminal of a nerve cell. This neurotransmitter, i.e., dopamine, will cross a synapse to dopamine receptors located on the post-synaptic dendrite of another neuron. Then the action potential, i.e., "the message," can be sent to the next nerve cell, so on and so forth. The message, at least in this case, might control the blood flow to the brain. Notably, though, if a shortage of dopamine occurs, it could have significant implications, e.g., the brain could "freeze," and the individual could develop a "dithering personality," rendering his/her body relatively motionless. In contrast, an excess of dopamine is believed to cause disorders like "schizophrenia," which is a disorder associated with excessive excitability and other exaggerated symptoms (Ridley, 2000).
Getting back to the D4DR gene, the middle of it is thought to contain a variable repeat sequence that is 48 base pairs in length, and is repeated between 2 and 11 times. The significance of the repeat sequence is that the more the repeats that are present, the less effective the dopamine receptors will be at receiving the chemical dopamine. Hence, all of the findings mentioned above do seem to lend substantial support to the notion that one's personality may be a function of one's genetic makeup.
Interestingly, though variable amounts of dopamine could affect one's personality in various ways, it should not be assumed that such variances are always the result of genetic differences and/or genetic programming. More specifically, external factors could also play an important role in affecting or altering one's personality too. For instance, some hallucinogenic drugs have been found to stimulate the dopamine system. Consequently, too little dopamine or too much dopamine could render an individual to be bored easily or having a constant thirst for adventure, all because of the drugs that s/he might be using. In addition, low amounts of serotonin, possibly due to a lack of sunlight, particularly during the winter months, could also lead to less activity, and possibly depressed (or is it "depressing"? …