Jim Springer and Jim Lewis are identical twins from the United States who were separated at birth at four weeks old. Years later in 1979, in adulthood, they met and discovered how similar they are despite not growing up together.

“When they shared their stories they found that they both had childhood dogs named Toy… Both men married women named Linda, had been divorced and married second wives named Betty. Lewis named his first son James Allen, Springer named his James Alan…. Both of the Jameses worked as sheriff’s deputies. They both drank the same kind of beer and smoked the same brand of cigarettes. Both loved and hated the same sports and left regular love notes to their wives, made doll’s furniture in their basements, and constructed unusual circular benches around the trees in their gardens.”

The case of the Jim twins brings up the old age debate of nature vs nurture. Researchers and psychologists have been debating whether nature or nurture has the greatest impact on who we are and what we become. This debate is still argued today.

Nature vs nurture

Nature refers to our genes and the hereditary makeup that influence who we are and what we look like. This includes our personality characteristics and appearance.

Twin studies support that behavioural genetics – which is how heredity and environmental factors influence psychological characteristics – account for 40-50% of personality. An example of behavioural genetics would be by comparing the personality traits and the environment in which the Jim twins grew up.

Nurture refers to how our environment impacts who we are. This includes our culture, how we were raised, our childhood and our social relationships.

Since genetics accounts for 40-50% of personality, we’d expect that our environment accounts for the rest. But surprisingly that is not the case.

According to the book, Psychology: The Science of Mind and Behaviour, “… The key finding was that twins raised together and apart, whether identical or fraternal did not differ in their degree of
personality similarity. In fact, researchers have found that pairs of children who are raised within the same family are as different from one another as are pair of children who are randomly selected from the population.”

What this means is that even if you and your sibling grow up in the same household and are surrounded by the same people, it doesn’t mean that you will have the same experiences.

This doesn’t mean that shared environments don’t play an important role. These unique experiences and differences shape who we are. The nurture debate has found that “… shared-environments effect intelligence, attitudes, religious beliefs, occupational preferences, notions of masculinity and femininity, political attitudes, and health behaviours such as smoking and drinking.”

Nativism and empiricism

There are two extreme ends of the spectrum in the nature vs nurture debate.

Nativists are those who believe that the characteristics of humans are because of evolution and a person’s unique genes.

Empiricism supporters argue that the human mind is a blank slate and that as we grow and develop, it results in experiences that drive who we are. John B Watson, the psychologist who developed behaviourism, a school of thought rooted in empiricism, believed that people could be trained to do more and become anything irrespective of their genetics.

How nature and nurture interact

The most important factor that researchers do know is the interaction between heredity and the environment.

Height is an example that is influenced by both nature and nurture. So let’s say that if Jim Lewis was born into a family where everyone was tall, he may have inherited these genes. However, if he grew up in an environment where he didn’t receive proper nourishment, he might not have attained the height he could have had if he had grown up in a healthier environment.

So is it nature or nature?
Today many experts believe that both nature and nurture play a role in development and behaviour. We are who we are because of the genes that our parents pass down to us, but we are also who were are because of the environment we’re exposed to.

Like the Greek philosopher, Aristotle, once said, “Knowing yourself is the beginning of all wisdom.” When we know who we are and where we come from, we begin to thrive.

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Tell us: What do you think has the greater influence – nature or nurture?