While it is true that "everything psychological is simultaneously biological," 1 it is clear that our brain is engineered in an incalculable way by our experiences. Our choice of life and career paths are derived from both our genetic makeup and the environment we are raised in. The consistent patterns and stages in our development are also characterized by the adaptability and plasticity of the brain, which is not only sensitive to surrounding conditions, but relies on them to evolve. So, while studies on identical twins raised apart may reveal startling similarities, we must also be aware of their conspicuous differences that have been sculpted by their independent upbringings.
The brain is that part of the central nervous system that includes all the higher nervous centers. It regulates and controls bodily activities, receiving and interpreting sensory impulses, and transmitting information to the muscles and body organs. It is also the seat of consciousness, thought, memory, and emotion.
We can see that the very first exposures the brain receives from the environment are critical to its development, well before a baby is born. Teratogens, which are harmful agents, such as drugs or viruses, that may cross the normally protective placenta, can have a devastating impact on the future mental capacity of a person. For example, when an expectant mother indulges in social drinking there will be an impact on the baby's intelligence. In the more extreme case, FAS, or Fetal Alcohol Syndrome, caused by prenatal alcohol excess, is one of the primary causes of mental retardation. So, even in these extremely early stages of development our environment is shaping our future. The environment is affecting our brains in a monumental manner even at 8 weeks, when in spite of it's genetic programming, it is the most susceptible to external influences. Twin...