This famous phrase is often repeated in the halls of academia. It has become particularly important since the discovery of DNA; nature’s mechanism to pass on traits to the next generation. The question really asks to what degree are the traits we observe a product of DNA versus the environment. Much like the mind and body, it is a dichotomy formed from two inseparable concepts.
Increasingly modern genetics has demonstrated how DNA is influenced by the environment. Identical twins share the identical strands of DNA, yet exhibit unique traits as they grow older. Proteins manufactured by the DNA template may encode information and influence subsequent protein transcription in ways as yet unknown. In the early days of genetics, much of the DNA code was labelled “junk,” but subsequent research increasingly proves otherwise. Moreover, the longevity of each cell has been shown to be influenced by the environment. Cell death had been assumed to be programmed from birth, but it is now known that diet and lifestyle influence the core program.
On the other hand, the opposing process can be observed in the average American family. Even though family members share a nearly identical environment, each person is physically and mentally unique. Among identical twins, the inheritance of schizophrenia is only around fifty percent. If one identical twin develops schizophrenia, there is a fifty percent chance the other will fall ill as well. All other mental impairments, assumed to be congenital (from birth), exhibit less gene penetration than schizophrenia. The good news is that there is no congenital mental problem that affects over fifty percent of identical twins. Among nonidentical siblings, the incidence is always less than twenty five percent, which is what would be expected if both parents carried a recessive gene for a mental illness. If the child of suspected genetic carriers is reared in a different environment from the family (adoption), then the percentage typically falls below statistical significance.
Let us assume that schizophrenia is the one proven mental impairment that may be passed from parent to child. Even when reared apart, identical twin children of schizophrenic parents still have a nearly fifty percent chance of developing schizophrenia. Other psychological and neuropsychological impairments typically fade away when the identical twins are reared in different environments. Nonspecific environmental influences have ruined many a doctoral thesis. A genetic predisposition to develop a mental illness is just that; a slightly greater risk to develop a mental or cognitive impairment than the average person in the population. Of equal or greater importance is the environment that surrounds and influences the genetic information. A genetically schizophrenic person is less apt to express the maladaptive genes when reared in a supportive and minimally stressful environment. Conversely, when a strong a man as Admiral Bird was isolated at the South Pole, he began to hear voices and see images that were nonexistent.
There is no material that is impervious to the environment, and our genes are no exception. The direction of current research has amplified the extent to which nature and nurture are reciprocal influences, down to the molecular level. The genetic potential of the human brain has allowed us to shape and control the environment; more than any other creature known to this planet. The future of biochemical research will allow us to increasingly alter our own genetic programming. At this juncture, the nurturing human environment is directly influencing nature. Perhaps it is not wise to mess with mother nature, as the old saying goes. Messing with mother nature has, it must be admitted, put humans at the top of the food chain. We humans will “mess” with anything we can get our hands on, and nature is certainly close at hand. Let us hope that she declines to “mess” with us.