There is No “Versus” in Nature Versus Nurture

January 21, 2017 at 1:50 am Stephanie Wolek Leave a comment

The “nature versus nurture” debate is alive and well today, even though science has debunked the entire argument. This might seem surprising since people still claim that certain traits are from genetics while others are from the person’s upbringing. On one side, people theorize that genetics affect everything from a person’s personality to their medical problems. On the other side, there’s the theory that everything is determined by how a person is raised: their environment, family, and childhood experience. As with most debates, the truth lies somewhere in the middle—nature and nurture constantly interplay.

History

The concept of nature versus nurture was first popularized by John Locke, an English philosopher and doctor. He believed in the “blank slate” theory, which stated that all human behavioral traits were based on their environment and how they had been raised. Later in history, Darwinism was becoming widely accepted and this led scientists to believe that behavioral traits were due to genetics, not the individual’s environment. This theory stated that a person’s personality was caused by genes and already set in stone at birth. Both scientists and philosophers continued the nature versus nurture debate until modern times. Now, scientists generally agree that the argument is a fallacy and reality is much more complicated than genes versus environment.

Environment affects genes

Genes can be expressed differently depending on both the internal and external environment. A gene might be switched on or off depending on internal factors, such as age and hormone production. The external environment also has a huge impact—a large proportion of differences in gene expression are due to variation in environments and lifestyles. A well-known gene mutation in rabbits causes dark markings in certain spots but only if they were exposed to a cold climate. If the rabbits are housed in freezing temperatures, they may even develop extra pigmentation. This means that rabbits with identical gene mutations may not end up with the same set of markings. As for humans, scientists have identified the genes that control height but they sometimes work in odd combinations. Even in “predictable” gene situations, genetics only account for roughly 80% of human height variation. In other words, many traits can’t be explained completely by genetics.

Even in cases where a trait seems completely genetic and instinctual, environment still plays a role. Ducklings and goslings are known for a behavior called imprinting, in which they automatically bond to the first creature or object they see. This normally allows the baby birds to immediately recognize and follow their mothers, increasing their chance of survival. When young hatchlings are raised by humans, however, these “instinctual” genetic behaviors can be altered. In one famous experiment, a biologist raised goslings and allowed them to imprint on him. Once they reached adulthood and began looking for mates, they developed a preference for humans. In fact, they had little interest in interacting with other geese. This shows that while imprinting might be a genetic trait, it can be significantly modified by the environment.

Genes affect environment

Just as the environment can affect the expression of genes, genes may change the environment an individual winds up in. A gene might predispose someone to enjoy being outside, prompting them to develop an interest in hiking or camping. This exposure to the outdoors could in turn activate genes that help the person build a cold tolerance. There are genes linked to alcoholism, which may encourage a person to try alcohol—but the individual is never guaranteed to become an alcoholic.

Genes connected to reckless behaviors could put someone in more risky situations. Researchers have long known that individuals with bipolar disorder, an illness linked to a number of genes, tend to engage in riskier behaviors. Bipolar patients are more likely to find themselves in environments with people who use drugs—putting them at a higher risk of developing substance abuse problems. In this case, the genes didn’t directly cause addiction. The illness simply made it more likely that the individual would find themselves in a situation where they might be encouraged to try drugs. Interestingly, there are also plenty of people who carry the same genes but never develop a mental illness, providing further evidence that both genetics and environment play an equal role.

Twin Studies

Scientists no longer consider nature versus nurture to be a valid debate topic and twin studies confirm this viewpoint. Twin studies offer a rare opportunity to test whether or not a trait is primarily determined by genes. Even though identical twins will be genetically indistinguishable, they’ll end up with many different traits—even if raised in the same home.

Early twin studies allowed scientists to pinpoint some of the genes behind schizophrenia. Inheriting these “schizophrenia genes” greatly increases the chance of developing the illness, yet there are cases where one twin becomes schizophrenic while the other doesn’t. This led researchers to conclude that while there are strong genetic factors behind the disease, the environment and other unknown influences still play a role. Twin studies completely disprove the idea of human traits being completely based on genetics.

The idea of nature versus nurture is rooted in old, outdated science and philosophy. Modern research shows that environmental factors influence genetics, sometimes completely activating or deactivating a gene. There is no “versus” when talking about personality traits and inherited illnesses, both genetics and the environment influence how an individual develops.

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Sources: uchicago.edu, cell.com, genetics.org, nature.com, jamanetwork.com