The study of genetics, coupled with the science of human behavior (psychology), resulted in a debate as to the role of environment in creating the human mind, compared to the role of our inherited traits.

The debate has been so hot and long that if the previous sentence were offered to scientists, professors and clinicians, the next four hours would be spent arguing over what each word actually meant.

This long-standing, venerable contest is, of course, no contest at all. Evidence continues to mount that while genetic predispositions are powerfully important, they are essentially matched in influence by environmental factors, to result in what we casually refer to as “personality.”

As in so many aspects of the world, we speak about personality as if we truly know something about it, when in truth, even the concept of a personality is an unproven construct.

We say to our friend, “Oh, you know Frank. He has a difficult personality.” Or we think to ourselves, “I just don’t have an extroverted personality.” We use the term often, confident that we know what it means.

Actually, the whole weight of the psychological “community” — people who get paid to think about such things — was brought to bear recently in order to expand the number of recognized traits associated with “personality” by 25 per cent.

There were four behavioral axes for many years. Now there are five. At least there are five in the Western schools of theory about human behavior. Eastern philosophies count a much higher number. And the season of birth is important as well.

In recent years, the study of human behavior has advanced considerably, given the full mapping of the human genome (as well as other animals) and the proliferation of advanced instrumentation to measure what is going on physically, chemically and biologically within the organs that comprise what we refer to as the mind.

Studies of twins, for example, suggest that only about half of behavioral traits found in fully developed siblings is related to genetic predisposition. The rest is contributed by environmental factors: the nurture part of the equation.

And even those traits stemming from genetic predisposition are not inflexible. Given enough power in the environmental factors, heredity can be swamped. For example, if a person is born with a high aptitude for language skills, but is isolated from hearing speech for seven years after birth, that individual will have severely hampered ability to learn to read, speak, write or understand any language.

Conversely, if a person has suffered a physical injury to the area of the brain normally shown to associate with language skills, other parts of the brain can be essentially rewired to take on those tasks, depending upon the age of the person at the time of the trauma and the health of the neural systems within the brain. As psychologists say, the brain is “plastic,” able to adapt and adjust.

Learning theory is a field in which this debate is probably hottest. Psychologists who tend to favor nature as the predominant force in determining human behavior argue that the neural circuitry structure is predetermined.

They cite research which shows the brain developing along similar patterns and designs of connectivity, across all individuals in a species. They note that single genes have been identified which control the ability of organisms to perform certain complex behaviors.

Psychologists who favor nature, or the power of external factors acting upon the organism to determine an animal’s behavioral repertoire, point to studies that show how critical to human development these external factors are.

For example, the chemical and nutrient milieu within the amniotic sleeping bag of the developing embryo is considered environmental. It has been shown that imbalances in that fluid’s contents can greatly affect behavior later in life. And it’s been shown that the fetal heartbeat responds to sounds in the mother’s environment.

To complicate matters further, very recent studies have demonstrated that genes can change during the course of a human life.

They are not permanent, as previously thought. Genes do not change at a fast rate, mind you, or broadly. But DNA is altered through environmental factors that cause subtle, yet important changes that can then be passed on to successive cells, even to offspring. This new field is called the study of epigenetics.

So hereditary factors are affected by the environment, DNA isn’t static and scientists are having an increasingly difficult time defining what is truly innate versus exogenous. This is why I find it difficult to form a static view of human behavior.

The only thing I know for sure is that whenever there is a contest between one explanation of behavior and another, both explanations are wrong, taken in isolation. The answer is never one or the other.

Nature versus nurture is a nonsensical proposition to start with. It’s always both.

Sewitch is an entrepreneur and business psychologist. He serves as the vice president of global organization development for WD-40 Company. Sewitch can be reached at sewitch1@cox.net